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Rhamnolipids (RLs) are widely used biosurfactants produced mainly by Pseudomonas aeruginosa and Burkholderia spp. in the form of mixtures of diverse congeners. The global transcriptional regulator gene irrE from radiation-tolerant extremophiles has been widely used as a stress-resistant element to construct robust producer strains and improve their production performance. A PrhlA-irrE cassette was constructed to express irrE genes in the Pseudomonas aeruginosa YM4 of the rhamnolipids producer strain. We found that the expression of irrE of Deinococcus radiodurans in the YM4 strain not only enhanced rhamnolipid production and the strain's tolerance to environmental stresses, but also changed the composition of the rhamnolipid products. The synthesized rhamnolipids reached a maximum titer of 26 g/L, about 17.9% higher than the original, at 48 h. The rhamnolipid production of the recombinant strain was determined to be mono-rhamnolipids congener Rha–C10–C12, accounting for 94.1% of total products. The critical micelle concentration (CMC) value of the Rha–C10–C12 products was 62.5 mg/L and the air-water surface tension decreased to 25.5 mN/m. The Rha–C10–C12 products showed better emulsifying activity on diesel oil than the original products. This is the first report on the efficient production of the rare mono-rhamnolipids congener Rha–C10–C12 and the first report that the global regulator irrE can change the components of rhamnolipid products in Pseudomonas aeruginosa. [ABSTRACT FROM AUTHOR]

Six angucyclines including three unreported compounds (1–3) were isolated from Streptomyces sp. XS-16 by overexpressing the native global regulator of SCrp (cyclic AMP receptor). The structures were characterized based on nuclear magnetic resonance (NMR) and spectrometry analysis and assisted by electronic circular dichroism (ECD) calculations. All compounds were tested for their antitumor and antimicrobial activities, and compound 1 showed different inhibitory activities against various tumor cell lines with IC50 values ranging from 0.32 to 5.33 μM. [ABSTRACT FROM AUTHOR]

Orc1-2 is a non-initiator ortholog of archaeal/eukaryotic Orc1 proteins, which functions as a global regulator in DNA damage-responsive (DDR) expression. As for Orc1 initiators, the DDR regulator harbors an AAA+ ATPase domain, an Initiator-Specific Motif (ISM) and a winged-helix (wH) DNA-binding domain, which are also organized in a similar fashion. To investigate how Orc1-2 mediates the DDR regulation, the orc1-2 mutants inactivating each of these functional domains were constructed with Saccharolobus islandicus and genetically characterized. We found that disruption of each functional domain completely abolished the DDR regulation in these orc1-2 mutants. Strikingly, inactivation of ATP hydrolysis of Orc1-2 rendered an inviable mutant. However, the cell lethality can be suppressed by the deficiency of the DNA binding in the same protein, and it occurs independent of any DNA damage signal. Mutant Orc1-2 proteins were then obtained and investigated for DNA-binding in vitro. This revealed that both the AAA+ ATPase and the wH domains are involved in DNA-binding, where ISM and R381R383 in wH are responsible for specific DNA binding. We further show that Orc1-2 regulation occurs in two distinct steps: (a) eliciting cell division inhibition at a low Orc1-2 content, and this regulation is switched on by ATP binding and turned off by ATP hydrolysis; any failure in turning off the regulation leads to growth inhibition and cell death; (b) activation of the expression of DDR gene encoding DNA repair proteins at an elevated level of Orc1-2. [ABSTRACT FROM AUTHOR]

Streptomyces can produce a wealth of pharmaceutically valuable antibiotics and other bioactive compounds. Production of most antibiotics is generally low due to the rigorously controlled regulatory networks, in which global/pleiotropic and cluster-situated regulatory proteins coordinate with various intra- and extracellular signals. Thus, mining new antibiotic regulatory proteins, particularly the ones that are widespread, is essential for understanding the regulation of antibiotic biosynthesis. Here, in the biopesticide milbemycin producing strain Streptomyces bingchenggensis, a novel global/pleiotropic regulatory protein, SspH, a single domain protein containing only the HATPase domain, was identified as being involved in controlling antibiotic biosynthesis. The sspH overexpression inhibited milbemycin production by repressing the expression of milbemycin biosynthetic genes. The sspH overexpression also differentially influenced the expression of various antibiotic biosynthetic core genes. Site-directed mutagenesis revealed that the HATPase domain was essential for SspH's function, and mutation of the conserved amino acid residues N54A and D84A led to the loss of SspH function. Moreover, cross-overexpression experiments showed that SspH and its orthologs, SCO1241 from Streptomyces coelicolor and SAVERM_07097 from Streptomyces avermitilis, shared identical functionality, and all exerted a positive effect on actinorhodin production but a negative effect on avermectin production, indicating that SspH-mediated differential control of antibiotic biosynthesis may be widespread in Streptomyces. This study extended our understanding of the regulatory network of antibiotic biosynthesis and provided effective targets for future antibiotic discovery and overproduction. [ABSTRACT FROM AUTHOR]

Integrons are considered hot spots for bacterial evolution, since these platforms allow one-step genomic innovation by capturing and expressing genes that provide advantageous novelties, such as antibiotic resistance. The acquisition and shuffling of gene cassettes featured by integrons enable the population to rapidly respond to changing selective pressures. However, in order to avoid deleterious effects and fitness burden, the integron activity must be tightly controlled, which happens in an elegant and elaborate fashion, as discussed in detail in the present review. Here, we aimed to provide an up-to-date overview of the complex regulatory networks that permeate the expression and functionality of integrons at both transcriptional and translational levels. It was possible to compile strong shreds of evidence clearly proving that these versatile platforms include functions other than acquiring and expressing gene cassettes. The well-balanced mechanism of integron expression is intricately related with environmental signals, host cell physiology, fitness, and survival, ultimately leading to adaptation on the demand. [ABSTRACT FROM AUTHOR]

Overexpression of the global regulator LaeA in a marine-derived fungal strain of Penicillium dipodomyis YJ-11 induced obvious morphological changes and metabolic variations. Further chemical investigation of the mutant strain afforded a series of sorbicillinoids including two new ones named 10,11-dihydrobislongiquinolide ( 1 ) and 10,11,16,17-tetrahydrobislongiquinolide ( 2 ), as well as four known analogues, bislongiquinolide ( 3 ), 16,17-dihydrobislongiquinolide ( 4 ), sohirnone A ( 5 ), and 2',3'-dihydrosorbicillin ( 6 ). The results support that the global regulator LaeA is a useful tool in activating silent gene clusters in Penicillium strains to obtain previously undiscovered compounds.

Aeromonas hydrophila is an important aquatic microorganism that can cause fish hemorrhagic septicemia. In this study, we identified a novel LysR family transcriptional regulator (LahS) in the A. hydrophila Chinese epidemic strain NJ-35 from a library of 947 mutant strains. The deletion of lahS caused bacteria to exhibit significantly decreased hemolytic activity, motility, biofilm formation, protease production, and anti-bacterial competition ability when compared to the wild-type strain. In addition, the determination of the fifty percent lethal dose (LD50) in zebrafish demonstrated that the lahS deletion mutant (ΔlahS) was highly attenuated in virulence, with an approximately 200-fold increase in LD50 observed as compared with that of the wild-type strain. However, the ΔlahS strain exhibited significantly increased antioxidant activity (six-fold). Label-free quantitative proteome analysis resulted in the identification of 34 differentially expressed proteins in the ΔlahS strain. The differentially expressed proteins were involved in flagellum assembly, metabolism, redox reactions, and cell density induction. The data indicated that LahS might act as a global regulator to directly or indirectly regulate various biological processes in A. hydrophila NJ-35, contributing to a greater understanding the pathogenic mechanisms of A. hydrophila. [ABSTRACT FROM AUTHOR]