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Biological nitrogen fixation in legume plants depends on the diversity of rhizobia present in the soil. Rhizobial strains exhibit specificity towards host plants and vary in their capacity to fix nitrogen. The increasing interest in rhizobia diversity has prompted studies of their phylogenetic relations. Molecular identification of Rhizobium is quite complex, requiring multiple gene markers to be analysed to distinguish strains at the species level or to predict their host plant. In this research, 50 rhizobia isolates were obtained from the root nodules of five different Pisum sativum L. genotypes ("Bagoo", "Respect", "Astronaute", "Lina DS", and "Egle DS"). All genotypes were growing in the same field, where ecological farming practices were applied, and no commercial rhizobia inoculants were used. The influence of rhizobial isolates on pea root nodulation and dry biomass accumulation was determined. 16S rRNA gene, two housekeeping genes recA and atpD, and symbiotic gene nodC were analysed to characterize rhizobia population. The phylogenetic analysis of 16S rRNA gene sequences showed that 46 isolates were linked to Rhizobium leguminosarum; species complex 1 isolate was identified as Rhizobium nepotum, and the remaining 3 isolates belonged to Rahnella spp., Paenarthrobacter spp., and Peribacillus spp. genera. RecA and atpD gene analysis showed that the 46 isolates identified as R. leguminosarum clustered into three genospecies groups (B), (E) and (K). Isolates that had the highest influence on plant dry biomass accumulation clustered into the (B) group. NodC gene phylogenetic analysis clustered 46 R. leguminosarum isolates into 10 groups, and all isolates were assigned to the R. leguminosarum sv. viciae. [ABSTRACT FROM AUTHOR]

Aim Ohmic heating (OH) (i.e. heating by electric field) more effectively kills bacterial spores than traditional wet heating, yet its mechanism remains poorly understood. This study investigates the accelerated spore inactivation mechanism using genetically modified spores. Methods and results We investigated the effects of OH and conventional heating (CH) on various genetically modified strains of Bacillus subtilis : isogenic PS533 (wild type_1), PS578 [lacking spores' α/β-type small acid-soluble proteins (SASP)], PS2318 (lacking recA , encoding a DNA repair protein), isogenic PS4461 (wild type_2), and PS4462 (having the 2Duf protein in spores, which increases spore wet heat resistance and decreases spore inner membrane fluidity). Removal of SASP brought the inactivation profiles of OH and CH closer, suggesting the interaction of these proteins with the field. However, the reemergence of a difference between CH and OH killing for SASP-deficient spores at the highest tested field strength suggested there is also interaction of the field with another spore core component. Additionally, RecA-deficient spores yielded results like those with the wild-type spores for CH, while the OH resistance of this mutant increased at the lower tested temperatures, implying that RecA or DNA are a possible additional target for the electric field. Addition of the 2Duf protein markedly increased spore resistance both to CH and OH, although some acceleration of killing was observed with OH at 50 V/cm. Conclusions In summary, both membrane fluidity and interaction of the spore core proteins with electric field are key factors in enhanced spore killing with electric field-heat combinations. [ABSTRACT FROM AUTHOR]

Short‐Patch Double Illegitimate Recombination (SPDIR) has been recently identified as a rare mutation mechanism. During SPDIR, ectopic DNA single‐strands anneal with genomic DNA at microhomologies and get integrated during DNA replication, presumably acting as primers for Okazaki fragments. The resulting microindel mutations are highly variable in size and sequence. In the soil bacterium Acinetobacter baylyi, SPDIR is tightly controlled by genome maintenance functions including RecA. It is thought that RecA scavenges DNA single‐strands and renders them unable to anneal. To further elucidate the role of RecA in this process, we investigate the roles of the upstream functions DprA, RecFOR, and RecBCD, all of which load DNA single‐strands with RecA. Here we show that all three functions suppress SPDIR mutations in the wildtype to levels below the detection limit. While SPDIR mutations are slightly elevated in the absence of DprA, they are strongly increased in the absence of both DprA and RecA. This SPDIR‐avoiding function of DprA is not related to its role in natural transformation. These results suggest a function for DprA in combination with RecA to avoid potentially harmful microindel mutations, and offer an explanation for the ubiquity of dprA in the genomes of naturally non‐transformable bacteria. [ABSTRACT FROM AUTHOR]

Strengthening the expression level of integrated genes on the genome is crucial for consistently expressing key enzymes in microbial cell factories for efficient bioproduction in synthetic biology. In comparison to plasmid-based multi-copy expression, the utilization of chromosomal multi-copy genes offers increased stability of expression level, diminishes the metabolic burden on host cells, and enhances overall genetic stability. In this study, we developed the “BacAmp”, a stabilized gene integration expression and copy number amplification system for high-level expression in Bacillus subtilis, which was achieved by employing a combination of repressor and non-natural amino acids (ncAA)-dependent expression system to create a reversible switch to control the key gene recA for homologous recombination. When the reversible switch is turned on, genome editing and gene amplification can be achieved. Subsequently, the reversible switch was turned off therefore stabilizing the gene copy number. The stabilized gene amplification system marked by green fluorescent protein, achieved a 3-fold increase in gene expression by gene amplification and maintained the average gene copy number at 10 after 110 generations. When we implemented the gene amplification system for the regulation of N-acetylneuraminic acid (NeuAc) synthesis, the copy number of the critical gene increased to an average of 7.7, which yielded a 1.3-fold NeuAc titer. Our research provides a new avenue for gene expression in synthetic biology and can be applied in metabolic engineering in B. subtilis.

Aim Recombinase RecA and its homologs play a key role in homologous recombination DNA repair and revive stalled replication fork DNA synthesis. RecA plays an essential role in the evolution of antibiotic-resistant strains via stress-induced DNA repair mechanisms during the SOS response. Accordingly, RecA has become an attractive target to slow down antibiotic resistance rates and prevent mutations in pathogenic bacterial species. Methods and results We employed RecA conserved activities: DNA binding, displacement loop formation, strand exchange, ATP hydrolysis, and LexA cleavage, to elucidate the inhibitory role of gallic acid on Staphylococcus aureus RecA functions. Gallic acid inhibition of the SOS response by western blot analysis and its antibacterial activity were measured. The gallic acid inhibited all the canonical activities of S. aureus RecA protein. Conclusion The natural phenolic compound gallic acid interferes with RecA protein DNA complex formation and inhibits activities such as displacementloop formation, strand exchange reaction, ATP hydrolysis, and coprotease activity of S. aureus. Additionally, gallic acid can obstruct ciprofloxacin-induced RecA expression and eventually confer the inhibitory role of gallic acid in the SOS survival mechanism in S. aureus. [ABSTRACT FROM AUTHOR]

Bordetella holmesii is a bacterium recently recognized in 1995. It is a gram-negative coccobacillus that can cause pertussis-like symptoms in humans as well as invasive infections. It is often confused with Bordetella pertussis because routine diagnostic tests for whooping cough are not species-specific. The prevalence of B. holmesii as a cause of pertussis has increased in several countries. Therefore, B. holmesii assays are important for determining the epidemiology of pertussis, for the choice of an effective treatment, and for detecting vaccination failures. [ABSTRACT FROM AUTHOR]

Linear dichroism spectroscopy is used to investigate the structure of RecA family recombinase filaments (RecA and Rad51 proteins) with DNA for clarifying the molecular mechanism of DNA strand exchange promoted by these proteins and its activation. The measurements show that the recombinases promote the perpendicular base orientation of single‐stranded DNA only in the presence of activators, indicating the importance of base orientation in the reaction. We summarize the results and discuss the role of DNA base orientation. [ABSTRACT FROM AUTHOR]

The adaptation of Salmonella enterica serovar Typhimurium to stress conditions involves expression of genes within the regulon of the alternative sigma factor RpoN (σ54). RpoN-dependent transcription requires an activated bacterial enhancer binding protein (bEBP) that hydrolyzes ATP to remodel the RpoN-holoenzyme-promoter complex for transcription initiation. The bEBP RtcR in S. Typhimurium strain 14028s is activated by genotoxic stress to direct RpoN-dependent expression of the RNA repair operon rsr-yrlBA-rtcBA. The molecular signal for RtcR activation is an oligoribonucleotide with a 3'-terminal 2',3'-cyclic phosphate. We show in S. Typhimurium 14028s that the molecular signal is not a direct product of nucleic acid damage, but signal generation is dependent on a RecA-controlled SOS-response pathway, specifically, induction of prophage Gifsy-1. A genome-wide mutant screen and utilization of Gifsy prophage-cured strains indicated that the nucleoid-associated protein Fis and the Gifsy-1 prophage significantly impact RtcR activation. Directed-deletion analysis and genetic mapping by transduction demonstrated that a three-gene region (STM14_3218-3220) in Gifsy-1, which is variable between S. Typhimurium strains, is required for RtcR activation in strain 14028s and that the absence of STM14_3218-3220 in the Gifsy-1 prophages of S. Typhimurium strains LT2 and 4/74, which renders these strains unable to activate RtcR during genotoxic stress, can be rescued by complementation in cis by the region encompassing STM14_3218-3220. Thus, even though RtcR and the RNA repair operon are highly conserved in Salmonella enterica serovars, RtcR-dependent expression of the RNA repair operon in S. Typhimurium is controlled by a variable region of a prophage present in only some strains. IMPORTANCE The transcriptional activator RtcR and the RNA repair proteins whose expression it regulates, RtcA and RtcB, are widely conserved in Proteobacteria. In Salmonella Typhimurium 14028s, genotoxic stress activates RtcR to direct RpoN-dependent expression of the rsr-yrlBA-rtcBA operon. This work identifies key elements of a RecA-dependent pathway that generates the signal for RtcR activation in strain 14028s. This signaling pathway requires the presence of a specific region within the prophage Gifsy-1, yet this region is absent in most other wild-type Salmonella strains. Thus, we show that the activity of a widely conserved regulatory protein can be controlled by prophages with narrow phylogenetic distributions. This work highlights an underappreciated phenomenon where bacterial physiological functions are altered due to genetic rearrangement of prophages.

Infections caused by Acinetobacter baumannii, a Gram‐negative opportunistic pathogen, are difficult to eradicate due to the bacterium's propensity to quickly gain antibiotic resistances and form biofilms, a protective bacterial multicellular community. The A. baumannii DNA damage response (DDR) mediates the antibiotic resistance acquisition and regulates RecA in an atypical fashion; both RecALow and RecAHigh cell types are formed in response to DNA damage. The findings of this study demonstrate that the levels of RecA can influence formation and dispersal of biofilms. RecA loss results in surface attachment and prominent biofilms, while elevated RecA leads to diminished attachment and dispersal. These findings suggest that the challenge to treat A. baumannii infections may be explained by the induction of the DDR, common during infection, as well as the delicate balance between maintaining biofilms in low RecA cells and promoting mutagenesis and dispersal in high RecA cells. This study underscores the importance of understanding the fundamental biology of bacteria to develop more effective treatments for infections. [ABSTRACT FROM AUTHOR]

Deinococcus radiodurans exhibits remarkable survival under extreme conditions, including ionizing radiation, desiccation, and various DNA-damaging agents. It employs unique repair mechanisms, such as single-strand annealing (SSA) and extended synthesis-dependent strand annealing (ESDSA), to efficiently restore damaged genome. In this study, we investigate the role of the natural transform ation-specific protein DprA in DNA repair pathways following acute gamma radiation exposure. Our findings demonstrate that the absence of DprA leads to rapid repair of gamma radiationinduced DNA double-strand breaks primarily occur through SSA repair pathway. Additionally, our findings suggest that the DprA protein may hinder both the SSA and ESDSA repair pathways, albeit in distinct manners. Overall, our results highlight the crucial function of DprA in the selection between SSA and ESDSA pathways for DNA repair in heavily irradiated D. radiodurans. [ABSTRACT FROM AUTHOR]

Biological nitrogen fixation in legume plants depends on the diversity of rhizobia present in the soil. Rhizobial strains exhibit specificity towards host plants and vary in their capacity to fix nitrogen. The increasing interest in rhizobia diversity has prompted studies of their phylogenetic relations. Molecular identification of Rhizobium is quite complex, requiring multiple gene markers to be analysed to distinguish strains at the species level or to predict their host plant. In this research, 50 rhizobia isolates were obtained from the root nodules of five different Pisum sativum L. genotypes (“Bagoo”, “Respect”, “Astronaute”, “Lina DS”, and “Egle DS”). All genotypes were growing in the same field, where ecological farming practices were applied, and no commercial rhizobia inoculants were used. The influence of rhizobial isolates on pea root nodulation and dry biomass accumulation was determined. 16S rRNA gene, two housekeeping genes recA and atpD, and symbiotic gene nodC were analysed to characterize rhizobia population. The phylogenetic analysis of 16S rRNA gene sequences showed that 46 isolates were linked to Rhizobium leguminosarum; species complex 1 isolate was identified as Rhizobium nepotum, and the remaining 3 isolates belonged to Rahnella spp., Paenarthrobacter spp., and Peribacillus spp. genera. RecA and atpD gene analysis showed that the 46 isolates identified as R. leguminosarum clustered into three genospecies groups (B), (E) and (K). Isolates that had the highest influence on plant dry biomass accumulation clustered into the (B) group. NodC gene phylogenetic analysis clustered 46 R. leguminosarum isolates into 10 groups, and all isolates were assigned to the R. leguminosarum sv. viciae.

Linear dichroism (LD) is a differential polarized light absorption spectroscopy used for studying filamentous molecules such as DNA and protein filaments. In this study, we review the applications of LD for the analysis of DNA-protein interactions. LD signals can be measured in a solution by aligning the sample using flow-induced shear force or a strong electric field. The signal generated is related to the local orientation of chromophores, such as DNA bases, relative to the filament axis. LD can thus assess the tilt and roll of DNA bases and distinguish intercalating from groove-binding ligands. The intensity of the LD signal depends upon the degree of macroscopic orientation. Therefore, DNA shortening and bending can be detected by a decrease in LD signal intensity. As examples of LD applications, we present a kinetic study of DNA digestion by restriction enzymes and structural analyses of homologous recombination intermediates, i.e., RecA and Rad51 recombinase complexes with single-stranded DNA. LD shows that the DNA bases in these complexes are preferentially oriented perpendicular to the filament axis only in the presence of activators, suggesting the importance of organized base orientation for the reaction. LD measurements detect DNA bending by the CRP transcription activator protein, as well as by the UvrB DNA repair protein. LD can thus provide information about the structures of protein-DNA complexes under various conditions and in real time. [ABSTRACT FROM AUTHOR]

Homologous recombination (HR) is a fundamental process common to all species. HR aims to faithfully repair DNA double strand breaks. HR involves the formation of nucleoprotein filaments on DNA single strands (ssDNA) resected from the break. The nucleoprotein filaments search for homologous regions in the genome and promote strand exchange with the ssDNA homologous region in an unbroken copy of the genome. HR has been the object of intensive studies for decades. Because multi-scale dynamics is a fundamental aspect of this process, studying HR is highly challenging, both experimentally and using computational approaches. Nevertheless, knowledge has built up over the years and has recently progressed at an accelerated pace, borne by increasingly focused investigations using new techniques such as single molecule approaches. Linking this knowledge to the atomic structure of the nucleoprotein filament systems and the succession of unstable, transient intermediate steps that takes place during the HR process remains a challenge; modeling retains a very strong role in bridging the gap between structures that are stable enough to be observed and in exploring transition paths between these structures. However, working on ever-changing long filament systems submitted to kinetic processes is full of pitfalls. This review presents the modeling tools that are used in such studies, their possibilities and limitations, and reviews the advances in the knowledge of the HR process that have been obtained through modeling. Notably, we will emphasize how cooperative behavior in the HR nucleoprotein filament enables modeling to produce reliable information. [ABSTRACT FROM AUTHOR]

Photorhabdus and Xenorhabdus are the bacterial symbionts of insect pathogenic nematodes, Heterorhabditis and Steinernema, respectively. This study aims to characterize the bacterial symbionts from Mizoram, North-east India and to evaluate their antibacterial potential. The bacterial isolates were characterized using recA and gyrB gene regions. The ethyl acetate extract of bacterial isolates was tested against pathogenic bacterial strains, viz. Escherichia coli (ATCC 10536), Klebsiella pneumoniae (ATCC 10031), Pseudomonas aeruginosa (ATCC 10145), and Bacillus subtilis (ATCC 11774) using disk diffusion method. Analysis of recA and gyrB genes revealed that the Photorhabdus isolates were P. hindustanensis, and P. namnaonensis. This study constitutes the first documentation of P. namnaonensis from India. The two isolated Xenorhabdus belong to X. vietnamensis and X. stockiae. The ethyl acetate extracts of the studied bacteria suppressed the development of all the microorganisms tested. Based on MIC and MBC values, the highest activity was exhibited by TS (P. hindustanensis) and TD (P. namnaonensis) isolates against P. aeruginosa and K. pneumoniae respectively. The lowest inhibitory activity was observed on both Xenorhabdus isolates (RF and PTS) against B. subtilis. This study focuses on the existence and identification of symbiotic bacteria from Mizoram, an Indo-Burma biodiversity hotspot region, and details their activity against different pathogenic bacteria. Since these metabolites could be potent antibiotics, further research is required to better understand the genetic information, chemical composition, and method of action against other microorganisms.

Homologous recombination (HR) is essential for genome stability and for maintaining genetic diversity. In eubacteria, RecA protein plays a key role during DNA repair, transcription, and HR. RecA is regulated at multiple levels, but majorly by RecX protein. Moreover, studies have shown RecX is a potent inhibitor of RecA and thus acts as an antirecombinase. Staphylococcus aureus is a major food-borne pathogen that causes skin, bone joint, and bloodstream infections. To date, RecX's role in S. aureus has remained enigmatic. Here, we show that S. aureus RecX (SaRecX) is expressed during exposure to DNA-damaging agents, and purified RecX protein directly interacts physically with RecA protein. The SaRecX is competent to bind with single-stranded DNA preferentially and double-stranded DNA feebly. Significantly, SaRecX impedes the RecA-driven displacement loop and inhibits formation of the strand exchange. Notably, SaRecX also abrogates adenosine triphosphate hydrolysis and abolishes the LexA coprotease activity. These findings highlight the role of the RecX protein as an antirecombinase during HR and play a pivotal role in regulation of RecA during the DNA transactions. [ABSTRACT FROM AUTHOR]

Photorhabdus and Xenorhabdus are the bacterial symbionts of insect pathogenic nematodes, Heterorhabditis and Steinernema, respectively. This study aims to characterize the bacterial symbionts from Mizoram, North-east India and to evaluate their antibacterial potential. The bacterial isolates were characterized using recA and gyrB gene regions. The ethyl acetate extract of bacterial isolates was tested against pathogenic bacterial strains, viz. Escherichia coli (ATCC 10536), Klebsiella pneumoniae (ATCC 10031), Pseudomonas aeruginosa (ATCC 10145), and Bacillus subtilis (ATCC 11774) using disk diffusion method. Analysis of recA and gyrB genes revealed that the Photorhabdus isolates were P. hindustanensis, and P. namnaonensis. This study constitutes the first documentation of P. namnaonensis from India. The two isolated Xenorhabdus belong to X. vietnamensis and X. stockiae. The ethyl acetate extracts of the studied bacteria suppressed the development of all the microorganisms tested. Based on MIC and MBC values, the highest activity was exhibited by TS (P. hindustanensis) and TD (P. namnaonensis) isolates against P. aeruginosa and K. pneumoniae respectively. The lowest inhibitory activity was observed on both Xenorhabdus isolates (RF and PTS) against B. subtilis. This study focuses on the existence and identification of symbiotic bacteria from Mizoram, an Indo-Burma biodiversity hotspot region, and details their activity against different pathogenic bacteria. Since these metabolites could be potent antibiotics, further research is required to better understand the genetic information, chemical composition, and method of action against other microorganisms. [ABSTRACT FROM AUTHOR]

Shiga toxin (Stx)-producing Escherichia coli (STEC) is a major cause of foodborne illness globally, and infection with serotype O157:H7 is associated with increased risk of hospitalization and death in the U.S. The Stxs are encoded on a temperate bacteriophage (stx-phage), and phage induction leads to Stx expression; subtype Stx2a in particular is associated with more severe disease. Our earlier studies showed significant levels of RecA-independent Stx2 production by STEC O157:H7 strain JH2010 (stx2astx2c), even though activated RecA is the canonical trigger for stx-phage induction. This study aimed to further compare and contrast RecA-independent toxin production in Stx2-producing clinical isolates. Deletion of recA in JH2010 resulted in higher in vitro supernatant cytotoxicity compared to that from JH2016ΔrecA, and the addition of the chelator ethylenediaminetetraacetic acid (EDTA) and various metal cations to the growth medium exacerbated the difference in cytotoxicity exhibited by the two deletion strains. Both the wild-type and ΔrecA deletion strains exhibited differential cytotoxicity in the feces of infected, streptomycin (Str)-treated mice. Comparison of the stx2a-phage predicted protein sequences from JH2010 and JH2016 revealed low amino acid identity of key phage regulatory proteins that are involved in RecA-mediated stx-phage induction. Additionally, other STEC isolates containing JH2010-like and JH2016-like stx2a-phage sequences led to similar Stx2 localization, as demonstrated by JH2010ΔrecA and JH2016ΔrecA, respectively. Deletion of the stx2a-phage regulatory region in the wild-type strains prevented the differential localization of Stx2 into the culture supernatant, a finding that suggests that the stx2a-phage regulatory region is involved in the differential ΔrecA phenotypes exhibited by the two strains. We hypothesize that the amino acid differences between the JH2010 and JH2016 phage repressor proteins (CIs) lead to structural differences that are responsible for differential interaction with RecA. Overall, we discovered that non-homologous stx2a-phage regulatory proteins differentially influence RecA-independent, and possibly RecA-dependent, Stx2 production. These findings emphasize the importance of studying non-homologous regulatory elements among stx2-phages and their influence on Stx2 production and virulence of STEC isolates. [ABSTRACT FROM AUTHOR]

Polyoxometalates have emerged as promising bactericidal agents. In the current study, the bactericidal activity of polyoxometalate K6[P2Mo18O62] against Escherichia coli (E. coli) O157:H7 and its possible underlying mechanisms were explored. The obtained results demonstrated that K6[P2Mo18O62] could effectively kill E. coli O157:H7 at millimolar levels. Moreover, K6[P2Mo18O62] treatment also induced significant increases in recA protein expression and further triggered characteristic apoptosis-like bacterial death events such as DNA fragmentation and phosphatidylserine exposure. In conclusion, polyoxometalate K6[P2Mo18O62] possesses a desirable antibacterial activity, and induction of bacterial apoptosis-like death might be involved in its underlying bactericidal mechanisms. [ABSTRACT FROM AUTHOR]

SUMMARY: Chloroplast is the site for transforming light energy to chemical energy. It also acts as a production unit for a variety of defense‐related molecules. These defense moieties are necessary to mount a successful counter defense against pathogens, including viruses. Previous studies indicated disruption of chloroplast homeostasis as a basic strategy of Begomovirus for its successful infection leading to the production of vein‐clearing, mosaic, and chlorotic symptoms in infected plants. Although begomoviral pathogenicity determinant protein Beta C1 (βC1) was implicated for pathogenicity, the underlying mechanism was unclear. Here we show that, begomoviral βC1 directly interferes with the host plastid homeostasis. βC1 induced DPD1, an organelle‐specific nuclease, implicated in nutrient salvage and senescence, as well as modulated the function of a major plastid genome maintainer protein RecA1, to subvert plastid genome. We show that βC1 was able to physically interact with bacterial RecA and its plant homolog RecA1, resulting in its altered activity. We observed that knocking‐down DPD1 during virus infection significantly reduced virus‐induced necrosis. These results indicate the presence of a strategy in which a viral protein alters host defense by targeting modulators of chloroplast DNA. We predict that the mechanism identified here might have similarities in other plant–pathogen interactions. Significance Statement: The interaction between viruses and their hosts involves an arms race to counter each other. We show how viruses destabilize chloroplasts to stop host defense signaling. [ABSTRACT FROM AUTHOR]

RecA family recombinases are the core enzymes in the process of homologous recombination, and their normal operation ensures the stability of the genome and the healthy development of organisms. The UvsX protein from bacteriophage T4 is a member of the RecA family recombinases and plays a central role in T4 phage DNA repair and replication, which provides an important model for the biochemistry and genetics of DNA metabolism. UvsX shares a high degree of structural similarity and function with RecA, which is the most deeply studied member of the RecA family. However, the detailed molecular mechanism of UvsX has not been resolved. In this study, a comprehensive all-atom molecular dynamics simulation of the UvsX protein dimer complex was carried out in order to investigate the conformational and binding properties of UvsX in combination with ATP and DNA, and the simulation of RecA was synchronized with the property comparison learning for UvsX. This study confirmed the highly conserved molecular structure characteristics and catalytic centers of RecA and UvsX, and also discovered differences in regional conformation, volatility and the ability to bind DNA between the two proteins at different temperatures, which would be helpful for the subsequent understanding and application of related recombinases. [ABSTRACT FROM AUTHOR]

The SOS response is a conserved stress response pathway that is triggered by DNA damage in the bacterial cell. Activation of this pathway can, in turn, cause the rapid appearance of new mutations, sometimes called hypermutation. We compared the ability of various SOS-inducing drugs to trigger the expression of RecA, cause hypermutation, and produce elongation of bacteria. During this study, we discovered that these SOS phenotypes were accompanied by the release of large amounts of DNA into the extracellular medium. The release of DNA was accompanied by a form of bacterial aggregation in which the bacteria became tightly enmeshed in DNA. We hypothesize that DNA release triggered by SOS-inducing drugs could promote the horizontal transfer of antibiotic resistance genes by transformation or by conjugation. [ABSTRACT FROM AUTHOR]

Heterozygous variants in the ATP1A3 gene are linked to well-known neurological phenotypes. There has been growing evidence for a separate phenotype associated with variants in residue Arg756—fever-induced paroxysmal weakness and encephalopathy (FIPWE) or relapsing encephalopathy with cerebellar ataxia (RECA). With only about 20 cases being reported, the clinical features associated with mutations at Arg756 have not been fully elucidated. We report a case of FIPWE with a p.Arg756Cys change in the ATP1A3 gene and a comparison of the clinical features, including electrophysiological examination, with previous cases. The 3-year-old male patient had normal psychomotor development, presenting with recurrent symptoms of generalized hypotonia with loss of gait, mutism, and dystonic movements only during febrile illnesses since 19 months of age. At 2.7 years of age, a third neurological decompensation episode occurred, during which electroencephalography (EEG) did not reveal high voltage slow waves or epileptiform discharge. Nerve conduction studies (NCS) also did not show latency delay or amplitude reduction. ATP1A3 exon sequencing showed a heterozygous p.Arg756Cys mutation. While the patient experienced repeated encephalopathy-like episodes, including severe hypotonia during febrile illness, EEG and NCS did not reveal any obvious abnormalities. These electrophysiological findings may represent an opportunity to suspect FIPWE and RECA. [ABSTRACT FROM AUTHOR]

Background: Ochrobactrum anthropi ( O. anthropi) is a Gram-negative, nonfermenting bacillus, which has been recovered from clinical samples worldwide. However, it has never been reported from any clinical sample in Egypt. To the best of our knowledge, we report for the first time, the isolation of O. anthropi from bloodstream infection of a 75-year-old female patient. Ochrobactrum anthropi identification was performed using Vitek-2 system (BioMérieux, Marcy l’Etoile, France), and confirmed using 16S rRNA sequencing. The organism was further classified as O. anthropi subclade I, using recA sequence analysis. Susceptibility testing was carried out using broth microdilution method, and the isolate was found to be resistant to both ceftazidime and cefepime. Molecular investigation of genes conferring resistance to the third and fourth generation cephalosporins, showed that the isolate harbored blaOCH-6 gene, and that blaTEM, blaSHV and blaCTX-M were not present. This work highlights the first isolation of O. anthropi from bloodstream infection in Alexandria, Egypt.

The diverse and large-scale application of disinfectants posed potential health risks and caused ecological damage during the 2019-nCoV pandemic, thereby increasing the demands for the development of disinfectants based on natural products, with low health risks and low aquatic toxicity. In the present study, a few natural naphthoquinones and their derivatives bearing the 1,4-naphthoquinone skeleton were synthesized, and their antibacterial activity against selected bacterial strains was evaluated. In vitro antibacterial activities of the compounds were investigated against Escherichia coli and Staphylococcus aureus. Under the minimum inhibitory concentration (MIC) of ⩽ 0.125 µmol/L for juglone (1a), 5,8-dimethoxy-1,4-naphthoquinone (1f), and 7-methyl-5-acetoxy-1,4-naphthoquinone (3c), a strong antibacterial activity against S. aureus was observed. All 1,4-naphthoquinone derivatives exhibited a strong antibacterial activity, with MIC values ranging between 15.625 and 500 µmol/L and EC50 values ranging between 10.56 and 248.42 µmol/L. Most of the synthesized compounds exhibited strong antibacterial activities against S. aureus. Among these compounds, juglone (1a) showed the strongest antibacterial activity. The results from mechanistic investigations indicated that juglone, a natural naphthoquinone, caused cell death by inducing reactive oxygen species production in bacterial cells, leading to DNA damage. In addition, juglone could reduce the self-repair ability of bacterial DNA by inhibiting RecA expression. In addition to having a potent antibacterial activity, juglone exhibited low cytotoxicity in cell-based investigations. In conclusion, juglone is a strong antibacterial agent with low toxicity, indicating that its application as a bactericidal agent may be associated with low health risks and aquatic toxicity. [ABSTRACT FROM AUTHOR]

Homologous recombination (HR) is a crucial mechanism of DNA strand exchange that promotes genetic repair and diversity in all kingdoms of life. Bacterial HR is driven by the universal recombinase RecA, assisted in the early steps by dedicated mediators that promote its polymerization on single-stranded DNA (ssDNA). In bacteria, natural transformation is a prominent HR-driven mechanism of horizontal gene transfer specifically dependent on the conserved DprA recombination mediator. Transformation involves internalization of exogenous DNA as ssDNA, followed by its integration into the chromosome by RecA-directed HR. How DprA-mediated RecA filamentation on transforming ssDNA is spatiotemporally coordinated with other cellular processes remains unknown. Here, we tracked the localization of fluorescent fusions to DprA and RecA in Streptococcus pneumoniae and revealed that both accumulate in an interdependent manner with internalized ssDNA at replication forks. In addition, dynamic RecA filaments were observed emanating from replication forks, even with heterologous transforming DNA, which probably represent chromosomal homology search. In conclusion, this unveiled interaction between HR transformation and replication machineries highlights an unprecedented role for replisomes as landing pads for chromosomal access of tDNA, which would define a pivotal early HR step for its chromosomal integration. [ABSTRACT FROM AUTHOR]

Recombinases are in part responsible for homologous recombination and genome integrity during DNA repair. DMC1 has a typical RecA domain, and belongs to the recombinase superfamily. The reactive oxygen species (ROS) as a potent DNA damage agent is produced during seed germination under stress conditions. DNA repair should be initiated immediately to allow for subsequent seedling development. In this study, we attempted to characterize the underlying mechanism of BrDMC1 responsiveness to salinity stress using the RNA interference approach in Brassica rapa (B. rapa). Bioinformatics and expression pattern analysis revealed that BrDMC1 only retained BrDMC1.A01 after the whole genome triplication (WGT) event and was primarily transcribed in flowers and seeds. BrDMC1 had high activity in the promoter region during germination, according to histochemical GUS staining. The data showed that salt treatment reduced the germination rate, weakened seed vigor and decreased antioxidant enzyme activity, but increased oxidative damage in BrDMC1-RNAi seeds. Furthermore, the expression of stress-responsive genes and damage repair genes was significantly different in transgenic lines exposed to salt stress. Therefore, BrDMC1 may respond to salt stress by controlling seed germination and the expression of stress-related and damage repair genes in B. rapa. [ABSTRACT FROM AUTHOR]

The aim of this research is to study the phenotype, genotype, treatment strategies, and short-term prognosis of Chinese children with ATP1A3 (Na+/K+-ATPase alpha 3 gene)-related disorders in Southwest China. Patients with pathogenic ATP1A3 variants identified using next-generation sequencing were registered at the Children's Hospital of Chongqing Medical University from December 2015 to May 2019. We followed them as a cohort and analyzed their clinical data. Eleven patients were identified with de novo pathogenic ATP1A3 heterozygous variants. One (c.2542 + 1G > T, splicing) has not been reported. Eight patients with alternating hemiplegia of childhood (AHC), one with cerebellar ataxia, areflexia, pes cavus, optic atrophy, and sensorineural hearing loss (CAPOS), and two with relapsing encephalopathy with cerebellar ataxia (RECA) were included. The initial manifestations of AHC included hemiplegia, oculomotor abnormalities, and seizures, and the most common trigger was an upper respiratory tract infection without fever. All patients had paroxysmal hemiplegic attacks during their disease course. The brain MRI showed no abnormalities. Six out of eight AHC cases reached a stable disease state after treatment. The initial symptom of the patient with CAPOS was ataxia followed by developmental regression, seizures, deafness, visual impairment, and dysarthria, and the brain MRI indicated mild cerebellar atrophy. No fluctuation was noted after using Acetazolamide. The initial manifestations of the two RECA cases were dystonia and encephalopathy, respectively. One manifested a rapid-onset course of dystonia triggered by a fever followed by dysarthria and action tremors, and independent walking was impossible. The brain MRI image was normal. The other one presented with disturbance of consciousness, seizures, sleep disturbance, tremor, and dyskinesias. The EEG revealed a slow background (δ activity), and the brain MRI result was normal. No response to Flunarizine was noted for them, and it took 61 and 60 months for them to reach a stable disease state, respectively. Conclusion: Pathogenic ATP1A3 variants play an essential role in the pathogenesis of Sodium–Potassium pump disorders, and AHC is the most common phenotype. The treatment strategies and prognosis depend on the phenotype categories caused by different variation sites and types. The correlation between the genotype and phenotype requires further exploration. What is Known: • Pathogenic heterozygous ATP1A3 variants cause a spectrum of neurological phenotypes, and ATP1A3-disorders are viewed as a phenotypic continuum presenting with atypical and overlapping features. • The genotype-phenotype correlation of ATP1A3-disorders remains unclear. What is New: • In this study, the genotypes and phenotypes of ATP1A3-related disorders from Southwest of China were described. The splice-site variation c.2542+1G>T was detected for the first time in ATP1A3-related disorders. • The prognosis of twins with AHC p. Gly947Arg was more serious than AHC cases with other variants, which was inconsistent with previous reports. The phenomenon indicated the diversity of the correlation between the genotype and phenotype. [ABSTRACT FROM AUTHOR]

In response to DNA damage, bacterial RecA protein forms filaments with the assistance of DinI protein. The RecA filaments stimulate the autocleavage of LexA, the repressor of more than 50 SOS genes, and activate the SOS response. During the late phase of SOS response, the RecA filaments stimulate the autocleavage of UmuD and λ repressor CI, leading to mutagenic repair and lytic cycle, respectively. Here, we determined the cryo-electron microscopy structures of Escherichia coli RecA filaments in complex with DinI, LexA, UmuD, and λCI by helical reconstruction. The structures reveal that LexA and UmuD dimers bind in the filament groove and cleave in an intramolecular and an intermolecular manner, respectively, while λCI binds deeply in the filament groove as a monomer. Despite their distinct folds and oligomeric states, all RecA filament binders recognize the same conserved protein features in the filament groove. The SOS response in bacteria can lead to mutagenesis and antimicrobial resistance, and our study paves the way for rational drug design targeting the bacterial SOS response. [ABSTRACT FROM AUTHOR]

Linear dichroism (LD) is a differential polarized light absorption spectroscopy used for studying filamentous molecules such as DNA and protein filaments. In this study, we review the applications of LD for the analysis of DNA-protein interactions. LD signals can be measured in a solution by aligning the sample using flow-induced shear force or a strong electric field. The signal generated is related to the local orientation of chromophores, such as DNA bases, relative to the filament axis. LD can thus assess the tilt and roll of DNA bases and distinguish intercalating from groove-binding ligands. The intensity of the LD signal depends upon the degree of macroscopic orientation. Therefore, DNA shortening and bending can be detected by a decrease in LD signal intensity. As examples of LD applications, we present a kinetic study of DNA digestion by restriction enzymes and structural analyses of homologous recombination intermediates, i.e., RecA and Rad51 recombinase complexes with single-stranded DNA. LD shows that the DNA bases in these complexes are preferentially oriented perpendicular to the filament axis only in the presence of activators, suggesting the importance of organized base orientation for the reaction. LD measurements detect DNA bending by the CRP transcription activator protein, as well as by the UvrB DNA repair protein. LD can thus provide information about the structures of protein-DNA complexes under various conditions and in real time.

Homologous recombination (HR) is a fundamental process common to all species. HR aims to faithfully repair DNA double strand breaks. HR involves the formation of nucleoprotein filaments on DNA single strands (ssDNA) resected from the break. The nucleoprotein filaments search for homologous regions in the genome and promote strand exchange with the ssDNA homologous region in an unbroken copy of the genome. HR has been the object of intensive studies for decades. Because multi-scale dynamics is a fundamental aspect of this process, studying HR is highly challenging, both experimentally and using computational approaches. Nevertheless, knowledge has built up over the years and has recently progressed at an accelerated pace, borne by increasingly focused investigations using new techniques such as single molecule approaches. Linking this knowledge to the atomic structure of the nucleoprotein filament systems and the succession of unstable, transient intermediate steps that takes place during the HR process remains a challenge; modeling retains a very strong role in bridging the gap between structures that are stable enough to be observed and in exploring transition paths between these structures. However, working on ever-changing long filament systems submitted to kinetic processes is full of pitfalls. This review presents the modeling tools that are used in such studies, their possibilities and limitations, and reviews the advances in the knowledge of the HR process that have been obtained through modeling. Notably, we will emphasize how cooperative behavior in the HR nucleoprotein filament enables modeling to produce reliable information.

Regulation of microbial symbiosis in the human intestinal tract is imperative to maintain overall human health and prevent dysbiosis-related diseases, such as inflammatory bowel disease and obesity. Short-chain fatty acids (SCFA) in the intestine are produced by bacterial fermentation and aid in inflammation reduction, dietary fiber digestion, and metabolizing nutrients for the colon. SCFA, notably acetate, butyrate, and propionate, are starting to be used in clinical interventions for GI diseases. While acetate has been shown to mitigate a stress response in the proteome of Escherichia coli cells, little is known about the effects of butyrate and propionate on the same cells. This study aims to evaluate the effects that butyrate and propionate have on the activation of stress promoters in E. coli when induced with a known stressor. Three different strains of E. coli containing the pUCD615 plasmid were used, each with a different promoter fused to the structural genes of the lac operon on the plasmid. Each promoter detected a unique stress response: grpE'::lux fusion (heat shock), recA'::lux fusion (SOS response), and katG'::lux fusion (oxidative damage). Activation of these stress promoters by treatment groups resulted in the emission of bioluminescence which was quantified and compared across treatment groups. All three SCFAs at 25 mM added to cultures prior to stressing the bacteria caused significantly lower bioluminescence levels when compared to the stressed culture without prior addition of SCFA. This indicates that these SCFAs may reduce the stress response in E. coli. [ABSTRACT FROM AUTHOR]

Helicases are ATP-driven molecular machines that directionally remodel nucleic acid polymers in all three domains of life. They are responsible for resolving double-stranded DNA (dsDNA) into single-strands, which is essential for DNA replication, nucleotide excision repair, and homologous recombination. RecD2 from Deinococcus radiodurans (DrRecD2) has important contributions to the organism's unusually high tolerance to gamma radiation and hydrogen peroxide. Although the results from X-ray Crystallography studies have revealed the structural characteristics of the protein, direct experimental evidence regarding the dynamics of the DNA unwinding process by DrRecD2 in the context of other accessory proteins is yet to be found. In this study, we have probed the exact binding event and processivity of DrRecD2 at single-molecule resolution using Protein-induced fluorescence enhancement (smPIFE) and Forster resonance energy transfer (smFRET). We have found that the protein prefers to bind at the 5′ terminal end of the single-stranded DNA (ssDNA) by Drift and has helicase activity even in absence of ATP. However, a faster and iterative mode of DNA unwinding was evident in presence of ATP. The rate of translocation of the protein was found to be slower on dsDNA compared to ssDNA. We also showed that DrRecD2 is recruited at the binding site by the single-strand binding protein (SSB) and during the unwinding, it can displace RecA from ssDNA. [ABSTRACT FROM AUTHOR]

While the molecular repertoire of the homologous recombination pathways is well studied, the search mechanism that enables recombination between distant homologous regions is poorly understood. Earlier work suggests that the recombinase RecA, an essential component for homology search, forms an elongated filament, nucleating at the break site. How this RecA structure carries out long-distance search remains unclear. Here, we follow the dynamics of RecA after induction of a single double-strand break on the Caulobacter chromosome. We find that the RecA-nucleoprotein filament, once formed, rapidly translocates in a directional manner in the cell, undergoing several pole-to-pole traversals, until homology search is complete. Concomitant with translocation, we observe dynamic variation in the length of the filament. Importantly in vivo, the RecA filament alone is incapable of such long-distance movement; both translocation and associated length variations are contingent on action of structural maintenance of chromosome (SMC)-like protein RecN, via its ATPase cycle. In summary, we have uncovered the three key elements of homology search driven by RecN: mobility of a finite segment of RecA, changes in filament length, and ability to conduct multiple pole-to-pole traversals, which together point to an optimal search strategy. [ABSTRACT FROM AUTHOR]

RecBCD helicase/nuclease supports replication fork progress via recombinational repair or linear DNA degradation, explaining recBC mutant synthetic lethality with replication elongation defects. Since replication initiation defects leave chromosomes without replication forks, these should be insensitive to the recBCD status. Surprisingly, we found that both Escherichia coli dnaA46(Ts) and dnaC2(Ts) initiation mutants at semi-permissive temperatures are also recBC-colethal. Interestingly, dnaA46 recBC lethality suppressors suggest underinitiation as the problem, while dnaC2 recBC suppressors signal overintiation. Using genetic and physical approaches, we studied the dnaA46 recBC synthetic lethality, for the possibility that RecBCD participates in replication initiation. Overproduced DnaA46 mutant protein interferes with growth of dnaAþ cells, while the residual viability of the dnaA46 recBC mutant depends on the auxiliary replicative helicase Rep, suggesting replication fork inhibition by the DnaA46 mutant protein. The dnaA46 mutant depends on linear DNA degradation by RecBCD, rather than on recombinational repair. At the same time, the dnaA46 defect also interacts with Holliday junction-moving defects, suggesting reversal of inhibited forks. However, in contrast to all known recBC-colethals, which fragment their chromosomes, the dnaA46 recBC mutant develops no chromosome fragmentation, indicating that its inhibited replication forks are stable. Physical measurements confirm replication inhibition in the dnaA46 mutant shifted to semi-permissive temperatures, both at the level of elongation and initiation, while RecBCD gradually restores elongation and then initiation. We propose that RecBCD-catalyzed resetting of inhibited replication forks allows replication to displace the "sticky" DnaA46(Ts) protein from the chromosomal DNA, mustering enough DnaA for new initiations. [ABSTRACT FROM AUTHOR]

Relapsing encephalopathy with cerebellar ataxia, neopterin, ATP1A3, RECA, rapid-onset dystonia parkinsonism, alternating hemiplegia of childhood, CAPOS, anti-GAD Keywords: ATP1A3; relapsing encephalopathy with cerebellar ataxia; RECA; rapid-onset dystonia parkinsonism; alternating hemiplegia of childhood; CAPOS; neopterin; anti-GAD EN ATP1A3 relapsing encephalopathy with cerebellar ataxia RECA rapid-onset dystonia parkinsonism alternating hemiplegia of childhood CAPOS neopterin anti-GAD 1120 1123 4 11/07/22 20221101 NES 221101 We report a 23-year-old man with relapsing encephalopathy with cerebellar ataxia (RECA) secondary to a mutation in I ATP1A3 i , characterized by fever related exacerbations associated with elevated CSF neopterin, and possible response to immunotherapy. Dystonia and tremor of the hands, bilateral upper limb dysmetria and intention tremor, and action myoclonus of the upper limbs. [Extracted from the article]

The increase in antibiotic resistance represents a major global challenge for our health systems and calls for alternative treatment options, such as antimicrobial light-based therapies. Blue light has shown promising results regarding the inactivation of a variety of microorganisms; however, most often, antimicrobial blue light (aBL) therapy is performed using wavelengths close to the UV range. Here we investigated whether inactivation was possible using blue light with a wavelength of 475 nm. Both Gram-positive and -negative bacterial strains were treated with blue light with fluences of 7.5–45 J/cm2. Interestingly, only some bacterial strains were susceptible to 475 nm blue light, which was associated with the lack of RecA, i.e., a fully functional DNA repair mechanism. We demonstrated that the insertion of the gene recA reduced the susceptibility of otherwise responsive bacterial strains, indicating a protective mechanism conveyed by the bacterial SOS response. However, mitigating this pathway via three known RecA inhibiting molecules (ZnAc, curcumin, and Fe(III)-PcTs) did not result in an increase in bactericidal action. Nonetheless, creating synergistic effects by combining a multitarget therapy, such as aBL, with an RecA targeting treatment could be a promising strategy to overcome the dilemma of antibiotic resistance in the future. [ABSTRACT FROM AUTHOR]

Shiga toxin (Stx)-producing Escherichia coli (STEC) is a major cause of foodborne illness globally, and infection with serotype O157:H7 is associated with increased risk of hospitalization and death in the U.S. The Stxs are encoded on a temperate bacteriophage (stx-phage), and phage induction leads to Stx expression; subtype Stx2a in particular is associated with more severe disease. Our earlier studies showed significant levels of RecA-independent Stx2 production by STEC O157:H7 strain JH2010 (stx2astx2c), even though activated RecA is the canonical trigger for stx-phage induction. This study aimed to further compare and contrast RecA-independent toxin production in Stx2-producing clinical isolates. Deletion of recA in JH2010 resulted in higher in vitro supernatant cytotoxicity compared to that from JH2016ΔrecA, and the addition of the chelator ethylenediaminetetraacetic acid (EDTA) and various metal cations to the growth medium exacerbated the difference in cytotoxicity exhibited by the two deletion strains. Both the wild-type and ΔrecA deletion strains exhibited differential cytotoxicity in the feces of infected, streptomycin (Str)-treated mice. Comparison of the stx2a-phage predicted protein sequences from JH2010 and JH2016 revealed low amino acid identity of key phage regulatory proteins that are involved in RecA-mediated stx-phage induction. Additionally, other STEC isolates containing JH2010-like and JH2016-like stx2a-phage sequences led to similar Stx2 localization, as demonstrated by JH2010ΔrecA and JH2016ΔrecA, respectively. Deletion of the stx2a-phage regulatory region in the wild-type strains prevented the differential localization of Stx2 into the culture supernatant, a finding that suggests that the stx2a-phage regulatory region is involved in the differential ΔrecA phenotypes exhibited by the two strains. We hypothesize that the amino acid differences between the JH2010 and JH2016 phage repressor proteins (CIs) lead to structural differences that are responsible for differential interaction with RecA. Overall, we discovered that non-homologous stx2a-phage regulatory proteins differentially influence RecA-independent, and possibly RecA-dependent, Stx2 production. These findings emphasize the importance of studying non-homologous regulatory elements among stx2-phages and their influence on Stx2 production and virulence of STEC isolates.

Polyoxometalates have emerged as promising bactericidal agents. In the current study, the bactericidal activity of polyoxometalate K6[P2Mo18O62] against Escherichia coli (E. coli) O157:H7 and its possible underlying mechanisms were explored. The obtained results demonstrated that K6[P2Mo18O62] could effectively kill E. coli O157:H7 at millimolar levels. Moreover, K6[P2Mo18O62] treatment also induced significant increases in recA protein expression and further triggered characteristic apoptosis-like bacterial death events such as DNA fragmentation and phosphatidylserine exposure. In conclusion, polyoxometalate K6[P2Mo18O62] possesses a desirable antibacterial activity, and induction of bacterial apoptosis-like death might be involved in its underlying bactericidal mechanisms.

ABSTRACT RecA plays a central role in DNA repair and is a main actor involved in homologous recombination (HR). In vivo, RecA forms filamentous structures termed “threads,” which are essential for HR, but whose nature is still ill defined. We show that RecA from Bacillus subtilis having lower ATP binding activity can still form nucleoprotein filaments in vitro, features lower dsDNA binding activity, but still retains most of wild type RecA activity in vivo. Contrarily, loss of ATPase activity strongly reduced formation of nucleoprotein filaments in vitro, and effectivity to repair double strand breaks (DSBs) in vivo. In the presence of wild type RecA protein, additionally expressed RecA with lowered ATPbinding activity only moderately affected RecA dynamics, while loss of ATPase activity leads to a large reduction of the formation of threads, as well as of their dynamic changes observed in a seconds-scale. Single molecule tracking of RecA revealed incorporation of freely diffusing and nonspecifically DNA-bound molecules into threads upon induction of a single DSB. This change of dynamics was highly perturbed in the absence of ATPase activity, revealing that filamentous forms of RecA as well as their dynamics depend on ATPase activity. Based on the idea that ATPase activity of RecA is most important for DNA strand exchange activity, our data suggest that extension and retraction of threads due is to many local strand invasion events during the search for sequences homologous to the induced DNA break site. IMPORTANCE Single-strand (ss) DNA binding ATPase RecA is the central recombinase in homologous recombination, and therefore essential for DNA repair pathways involving DNA strand exchange reactions. In several bacterial, RecA forms filamentous structures along the long axis of cells after induction of double strand breaks (DSBs) in the chromosome. These striking assemblies likely reflect RecA/ssDNA nucleoprotein filaments, which can extend and remodel within a time frame of few minutes. We show that ATPase activity of RecA is pivotal for these dynamic rearrangements, which include recruitment of freely diffusing molecules into low-mobile molecules within filaments. Our data suggest that ssDNA binding- and unbinding reactions are at the heart of RecA dynamics that power the dynamics of subcellular filamentous assemblies, leading to strand exchange reactions over a distance of several micrometers.

Shiga toxin (Stx)-producing enterohemorrhagic Escherichia coli (EHEC) cause gastrointestinal infection and, in severe cases, hemolytic uremic syndrome which may lead to death. There is, to-date, no therapy for this infection. Stx induces ATP release from host cells and ATP signaling mediates its cytotoxic effects. Apyrase cleaves and neutralizes ATP and its effect on Stx and EHEC infection was therefore investigated. Apyrase decreased bacterial RecA and dose-dependently decreased toxin release from E. coli O157:H7 in vitro, demonstrated by reduced phage DNA and protein levels. The effect was investigated in a mouse model of E. coli O157:H7 infection. BALB/c mice infected with Stx2-producing E. coli O157:H7 were treated with apyrase intraperitoneally, on days 0 and 2 post-infection, and monitored for 11 days. Apyrase-treated mice developed disease two days later than untreated mice. Untreated infected mice lost significantly more weight than those treated with apyrase. Apyrase-treated mice exhibited less colonic goblet cell depletion and apoptotic cells, as well as lower fecal ATP and Stx2, compared to untreated mice. Apyrase also decreased platelet aggregation induced by co-incubation of human platelet-rich-plasma with Stx2 and E. coli O157 lipopolysaccharide in the presence of collagen. Thus, apyrase had multiple protective effects, reducing RecA levels, stx2 and toxin release from EHEC, reducing fecal Stx2 and protecting mouse intestinal cells, as well as decreasing platelet activation, and could thereby delay the development of disease.

Antibiotics have a primary mode of actions, and most of them have a common secondary mode of action via reactive species (ROS and RNS) mediated DNA damage. Bacteria have been able to tolerate this DNA damage by SOS (Save-Our-Soul) response. RecA is the universal essential key protein of the DNA damage mediated SOS repair in various bacteria including ESKAPE pathogens. In addition, antibiotics also triggers activation of various other bacterial mechanisms such as biofilm formation, host dependent responses, persister subpopulation formation. These supporting the survival of bacteria in unfriendly natural conditions i.e. antibiotic presence. This review highlights the detailed mechanism of RecA mediated SOS response as well as role of RecA-LexA interaction in SOS response. The review also focuses on inter-connection between DNA damage repair pathway (like SOS response) with other survival mechanisms of bacteria such as host mediated RecA induction, persister-SOS interplay, and biofilm-SOS interplay. This understanding of inter-connection of SOS response with different other survival mechanisms will prove beneficial in targeting the SOS response for prevention and development of therapeutics against recalcitrant bacterial infections. The review also covers the significance of RecA as a promising potent therapeutic target for hindering bacterial SOS response in prevailing successful treatments of bacterial infections and enhancing the conventional antibiotic efficiency. [ABSTRACT FROM AUTHOR]

Serratia proteamaculans synthesizes the intracellular metalloprotease protealysin. This work was aimed at searching for bacterial substrates of protealysin among the proteins responsible for replication and cell division. We have shown that protealysin unlimitedly cleaves the SOS response protein RecA. Even 20% of the cleaved RecA in solution appears to be incorporated into the polymer of uncleaved monomers, preventing further polymerization and inhibiting RecA ATPase activity. Transformation of Escherichia coli with a plasmid carrying the protealysin gene reduces the bacterial UV survival up to 10 times. In addition, the protealysin substrate is the FtsZ division protein, found in both E. coli and Acholeplasma laidlawii, which is only 51% identical to E. coli FtsZ. Protealysin cleaves FtsZ at the linker between the globular filament-forming domain and the C-terminal peptide that binds proteins on the bacterial membrane. Thus, cleavage of the C-terminal segment by protealysin can lead to the disruption of FtsZ's attachment to the membrane, and thereby inhibit bacterial division. Since the protealysin operon encodes not only the protease, but also its inhibitor, which is typical for the system of interbacterial competition, we assume that in the case of penetration of protealysin into neighboring bacteria that do not synthesize a protealysin inhibitor, cleavage of FtsZ and RecA by protealysin may give S. proteamaculans an advantage in interbacterial competition. [ABSTRACT FROM AUTHOR]

Background: Ochrobactrum anthropi (O. anthropi) is a Gram-negative, nonfermenting bacillus, which has been recovered from clinical samples worldwide. However, it has never been reported from any clinical sample in Egypt. To the best of our knowledge, we report for the first time, the isolation of O. anthropi from bloodstream infection of a 75-year-old female patient. Ochrobactrum anthropi identification was performed using Vitek-2 system (BioMérieux, Marcy l'Etoile, France), and confirmed using 16S rRNA sequencing. The organism was further classified as O. anthropi subclade I, using recA sequence analysis. Susceptibility testing was carried out using broth microdilution method, and the isolate was found to be resistant to both ceftazidime and cefepime. Molecular investigation of genes conferring resistance to the third and fourth generation cephalosporins, showed that the isolate harbored blaOCH-6 gene, and that blaTEM, blaSHV and blaCTX-M were not present. This work highlights the first isolation of O. anthropi from bloodstream infection in Alexandria, Egypt. [ABSTRACT FROM AUTHOR]

RecA is a central enzyme of homologous recombination in bacteria, which plays a major role in DNA repair, natural transformation and SOS-response activation. RecA forms nucleoprotein filaments on single-stranded DNA with a highly conserved architecture that is also shared by eukaryotic recombinases. One of the key features of these filaments is the ability to switch between stretched and compressed conformations in response to ATP binding and hydrolysis. However, the functional role of such conformational changes is not fully understood. Structural data revealed that in the absence of ATP RecA binds DNA with the stoichiometry of 5 nucleotides per one monomer, while in the presence of ATP the binding stoichiometry is 3:1. Such differences suggest incompatibility of the active and inactive conformations, yet dynamic single-molecule studies demonstrated that ATP and apo conformations can be directly interconvertible. In the present work we use a single-molecule approach to address the features of inactive RecA nucleoprotein filaments formed de novo in the absence of nucleotide cofactors. We show that compressed RecA-DNA filaments can exist with both 5:1 and 3:1 binding stoichiometry which is determined by conditions of the filament assembly. However, only a 3:1 stoichiometry allows direct interconvertibility with the active ATP-bound conformation. • DNA tension promotes RecA-DNA interaction in the absence of ATP. • Inactive RecA filaments exist with 5:1 and 3:1 nt per monomer stoichiometry. • Only 3:1 DNA binding stoichiometry is interconvertible with the active conformation. • ATP promotes depolymerization of RecA filaments with 5:1 DNA binding stoichiometry. [ABSTRACT FROM AUTHOR]

Bacteria of the genus Pectobacterium are globally occurring pathogens that infect a broad spectrum of plants. The plant cell wall degrading enzymes allow them to cause diseases like soft rot and blackleg. Worldwide trade and exchange of plant material together with the accompanying microorganisms contributed to the rapid spread and consequently the acquisition of new traits by bacteria. The 161 pectinolytic strains were isolated from symptomless vegetables and ornamental plants acquired from Polish and foreign local food markets. All strains except four Dickeya isolates were identified as belonging to the Pectobacterium genus by PCR with species-specific primers and recA gene sequencing. The newly isolated bacteria were assigned to eight species, P. versatile (50 strains), P. carotovorum (33), P. brasiliense (27), P. atrosepticum (19), P. parmentieri (12), P. polaris (11), P. parvum (3) and P. odoriferum (2). ERIC PCR and phenotypic characteristics revealed high heterogeneity among P. carotovorum, P. brasiliense and P. versatile isolates. Moreover, a subset of the newly isolated strains was characterised by high tolerance to changing environmental conditions such as salinity, pH and water availability. These bacteria can effectively macerate the tissues of various plants, including potato, chicory and orchid. Our results indicate that Pectobacterium strains isolated from internationally traded, symptomless vegetables and ornamental plants have high potential for adaptation to adverse environmental conditions and to infect various host plants. These features may contribute to the success of the genus Pectobacterium in spreading between different climatic zones and facilitate the colonisation of different ecological niches. [ABSTRACT FROM AUTHOR]

Heterozygous variants in the ATP1A3 gene are linked to well-known neurological phenotypes. There has been growing evidence for a separate phenotype associated with variants in residue Arg756—fever-induced paroxysmal weakness and encephalopathy (FIPWE) or relapsing encephalopathy with cerebellar ataxia (RECA). With only about 20 cases being reported, the clinical features associated with mutations at Arg756 have not been fully elucidated. We report a case of FIPWE with a p.Arg756Cys change in the ATP1A3 gene and a comparison of the clinical features, including electrophysiological examination, with previous cases. The 3-year-old male patient had normal psychomotor development, presenting with recurrent symptoms of generalized hypotonia with loss of gait, mutism, and dystonic movements only during febrile illnesses since 19 months of age. At 2.7 years of age, a third neurological decompensation episode occurred, during which electroencephalography (EEG) did not reveal high voltage slow waves or epileptiform discharge. Nerve conduction studies (NCS) also did not show latency delay or amplitude reduction. ATP1A3 exon sequencing showed a heterozygous p.Arg756Cys mutation. While the patient experienced repeated encephalopathy-like episodes, including severe hypotonia during febrile illness, EEG and NCS did not reveal any obvious abnormalities. These electrophysiological findings may represent an opportunity to suspect FIPWE and RECA.

RecA family recombinases are the core enzymes in the process of homologous recombination, and their normal operation ensures the stability of the genome and the healthy development of organisms. The UvsX protein from bacteriophage T4 is a member of the RecA family recombinases and plays a central role in T4 phage DNA repair and replication, which provides an important model for the biochemistry and genetics of DNA metabolism. UvsX shares a high degree of structural similarity and function with RecA, which is the most deeply studied member of the RecA family. However, the detailed molecular mechanism of UvsX has not been resolved. In this study, a comprehensive all-atom molecular dynamics simulation of the UvsX protein dimer complex was carried out in order to investigate the conformational and binding properties of UvsX in combination with ATP and DNA, and the simulation of RecA was synchronized with the property comparison learning for UvsX. This study confirmed the highly conserved molecular structure characteristics and catalytic centers of RecA and UvsX, and also discovered differences in regional conformation, volatility and the ability to bind DNA between the two proteins at different temperatures, which would be helpful for the subsequent understanding and application of related recombinases.

Antibiotics and disinfectants resistance is acquired by activating RecA‐mediated DNA repair, which maintains ROS‐dependent DNA damage caused by the antimicrobial molecules. To increase the efficacy of different antimicrobials, an inhibitor can be developed against RecA protein. The present study aims to design a denovo inhibitor against RecA protein of Acinetobacter baumannii. Pharmacophore‐based screening, molecular mechanics, molecular dynamics simulation (MDS), retrosynthetic analysis, and combinatorial synthesis were used to design lead VTRA1.1 against RecA of A. baumannii. Pharmacophore models (structure‐based and ligand‐based) were created, and a phase library of FDA‐approved drugs was prepared. Screening of the phase library against these pharmacophore models selected thirteen lead molecules. These filtered leads were used for the denovo fragment‐based design, which produced 253 combinations. These designed molecules were further analyzed for its interaction with active site of RecA that selected a hybrid VTRA1. Further, retrosynthetic analysis and combinatorial synthesis produced 1000 analogs of VTRA1 by more than 100 modifications. These analogs were used for XP docking, binding free energy calculation, and MDS analysis which finally select lead VTRA1.1 against RecA protein. Further, mutations at the interacting residues of RecA with VTRA1.1, alter the unfolding rate of RecA, which suggests the binding of VTRA1.1 to these residues may alter the stability of RecA. It is also found that VTRA1.1 had reduced interaction of RecA with LexA and ssDNA polydT, showing the lead's efficacy in controlling the SOS response. Further, it was also observed that VTRA1.1 does not contain any predicted human off‐targets and no cytotoxicity to cell lines. As functional RecA is involved in antimicrobial resistance, denovo designed lead VTRA1.1 against RecA may be further developed as a significant combination for therapeutic uses against A. baumannii. [ABSTRACT FROM AUTHOR]

Introduction: The Burkholderia cepacia complex (BCC) bacteria are opportunistic pathogens that cause nosocomial infections and are especially dangerous for cystic fibrosis (CF) patients. Burkholderia contaminans is an emerging BCC species isolated from CF patients that also occurs as a contaminant in pharmaceutical and personal care products, sometimes linking it with outbreaks. Methodology: A total of 55 B. contaminans isolates from CF and non-CF patients in Argentina were identified by recA sequencing and MALDI TOF MS. A standardized Pulsed Field Gel Electrophoresis (PFGE) protocol was set up in order to assess genetic diversity, outbreak investigations, and possible clone persistence. Results: All isolates were identified as B. contaminans by both MALDI-TOF MS and recA sequence analysis. PFGE has enabled us to compare and determine the genetic relationship between B. contaminans isolates. Isolates were distributed in different PFGE clusters with evidence of the presence and persistence of a clone, over a period of 3 years, in the same hospital. This large hospital outbreak involved CF and non-CF patients. Moreover, PFGE results showed a good correlation between sporadic or outbreak-related isolates and the available epidemiological information. Conclusions: These findings highlight the importance of B. contaminans in Argentina and provide evidence for encouraging the surveillance of highly transmissible clones. The study also contributes to global knowledge about B. contaminans infections. [ABSTRACT FROM AUTHOR]

RecA protein mediates homologous recombination repair in bacteria through assembly of long helical filaments on ssDNA in an ATP-dependent manner. RecX, an important negative regulator of RecA, is known to inhibit RecA activity by stimulating the disassembly of RecA nucleoprotein filaments. Here we use a single-molecule approach to address the regulation of (Escherichia coli) RecA-ssDNA filaments by RecX (E. coli) within the framework of distinct conformational states of RecA-ssDNA filament. Our findings revealed that RecX effectively binds the inactive conformation of RecA-ssDNA filaments and slows down the transition to the active state. Results of this work provide new mechanistic insights into the RecX-RecA interactions and highlight the importance of conformational transitions of RecA filaments as an additional level of regulation of its biological activity.