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In photosynthesis, light energy is absorbed and transferred to the reaction center, ultimately leading to the reduction of quinone molecules through the electron transfer chain. The oxidation and reduction of quinones generate an electrochemical potential difference used for adenosine triphosphate synthesis. The trafficking of quinone/quinol molecules between electron transport components has been a long‐standing question. Here, an atomic‐level investigation into the molecular mechanism of quinol dissociation in the photosynthetic reaction center–light‐harvesting complex 1 (RC–LH1) supercomplexes from Rhodopseudomonas palustris, using classical molecular dynamics (MD) simulations combined with self‐random acceleration MD‐MD simulations and umbrella sampling methods, is conducted. Results reveal a significant increase in the mobility of quinone molecules upon reduction within RC–LH1, which is accompanied by conformational modifications in the local protein environment. Quinol molecules have a tendency to escape from RC–LH1 in a tail‐first mode, exhibiting channel selectivity, with distinct preferred dissociation pathways in the closed and open LH1 rings. Furthermore, comparative analysis of free energy profiles indicates that alternations in the protein environment accelerate the dissociation of quinol molecules through the open LH1 ring. In particular, aromatic amino acids form π‐stacking interactions with the quinol headgroup, resembling the key components in a conveyor belt system. This study provides insights into the molecular mechanisms that govern quinone/quinol exchange in bacterial photosynthesis and lays the framework for tuning electron flow and energy conversion to improve metabolic performance. [ABSTRACT FROM AUTHOR]

The document from Chemical Communications, published in 2024, provides a comprehensive list of contents for the issue. It includes profiles of contributors, highlights on surface properties of carbon nitride materials, feature articles on various topics such as reactivity, nanoassemblies, and catalysis, as well as communications on topics like intermolecular interactions, synthesis strategies, and catalytic processes. The journal aims to connect the world with the chemical sciences and invest profits back into the chemistry community, reflecting a commitment to advancing research in the field. [Extracted from the article]

Conjugated polymer coatings enhance bacteria with eco-friendly energy use. A new hybrid system boosts hydrogen production by Rhodopseudomonas palustris@polypyrrole (R. palustris@PPy) through interface electron transfer and hydrogel encapsulation. To maximize the output, we studied hydrogen metabolism using various techniques and found that conductive polymer modification facilitated electron transfer, affecting intracellular pathways. This technology offers enhanced green hydrogen production for sustainable energy. [ABSTRACT FROM AUTHOR]

With the rising demand for sustainable renewable resources, microorganisms capable of producing bioproducts such as bioplastics are attractive. While many bioproduction systems are well-studied in model organisms, investigating non-model organisms is essential to expand the field and utilize metabolically versatile strains. This investigation centers on Rhodopseudomonas palustris TIE-1, a purple non-sulfur bacterium capable of producing bioplastics. To increase bioplastic production, genes encoding the putative regulatory protein PhaR and the depolymerase PhaZ of the polyhydroxyalkanoate (PHA) biosynthesis pathway were deleted. Genes associated with pathways that might compete with PHA production, specifically those linked to glycogen production and nitrogen fixation, were deleted. Additionally, RuBisCO form I and II genes were integrated into TIE-1's genome by a phage integration system, developed in this study. Our results show that deletion of phaR increases PHA production when TIE-1 is grown photoheterotrophically with butyrate and ammonium chloride (NH4Cl). Mutants unable to produce glycogen or fix nitrogen show increased PHA production under photoautotrophic growth with hydrogen and NH4Cl. The most significant increase in PHA production was observed when RuBisCO form I and form I & II genes were overexpressed, five times under photoheterotrophy with butyrate, two times with hydrogen and NH4Cl, and two times under photoelectrotrophic growth with N2. In summary, inserting copies of RuBisCO genes into the TIE-1 genome is a more effective strategy than deleting competing pathways to increase PHA production in TIE-1. The successful use of the phage integration system opens numerous opportunities for synthetic biology in TIE-1. [ABSTRACT FROM AUTHOR]

The objective of this bovine peripheral blood study was a comparative assessment of the phagocytic activity of neutrophils and monocytes and of the intracellular killing capacity of neutrophils from cows given no probiotic and from cows which were administered a probiotic consisting of Saccharomyces cerevisiae, Lactobacillus acidophilus, Lactobacillus plantarum and Rhodopseudomonas palustris. These activity types were compared during different lactation periods. A cohort of 20 pregnant dairy cows was divided into two groups of 10. The experimental group consisted of cows fed a ration supplemented with probiotics, and the control group consisted of cows fed an unsupplemented ration. Blood was drawn six times: 7 days before dry off, 14 days before parturition, and 7, 21, 60 and 90 days postpartum (DPP). The phagocytic activity of neutrophils and monocytes and the oxidative burst activity of neutrophils were determined by flow cytometry in the peripheral blood of all examined cows. Phagocytosis testing revealed increased percentages of phagocytic neutrophils and monocytes in the experimental group at 21, 60 and 90 DPP (P-value < 0.01). The mean fluorescence intensity (MFI) values for neutrophils and monocytes were higher on all days of the study (P-value < 0.01). In oxidative burst testing, the percentages of detected neutrophils and their MFI were increased in the experimental group on all days (P-value < 0.01). The use of probiotics supported dairy cows' immunity throughout the whole experiment. Probiotic supplementation may limit the occurrence of infectious diseases in these animals. [ABSTRACT FROM AUTHOR]

Rhodopseudomonas palustris is a purple non-sulfide bacterium (PNSB), and some strains have been proven to promote plant growth. However, the mechanism underlying the effect of these PNSBs remains limited. Based on genetic information, R. palustris possesses the ability to produce pyrroloquinoline quinone (PQQ). PQQ is known to play a crucial role in stimulating plant growth, facilitating phosphorous solubilization, and acting as a reactive oxygen species scavenger. However, it is still uncertain whether growth conditions influence R. palustriss production of PQQ and other characteristics. In the present study, it was found that R. palustris exhibited a higher expression of genes related to PQQ synthesis under autotrophic culture conditions as compared to acetate culture conditions. Moreover, similar patterns were observed for phosphorous solubilization and siderophore activity, both of which are recognized to contribute to plant-growth benefits. However, these PNSB culture conditions did not show differences in Arabidopsis growth experiments, indicating that there may be other factors influencing plant growth in addition to PQQ content. Furthermore, the endophytic bacterial strains isolated from Arabidopsis exhibited differences according to the PNSB culture conditions. These findings imply that, depending on the PNSBs growing conditions, it may interact with various soil bacteria and facilitate their infiltration into plants.

Petroleum‐based plastics levy significant environmental and economic costs that can be alleviated with sustainably sourced, biodegradable, and bio‐based polymers such as polyhydroxyalkanoates (PHAs). However, industrial‐scale production of PHAs faces barriers stemming from insufficient product yields and high costs. To address these challenges, we must look beyond the current suite of microbes for PHA production and investigate non‐model organisms with versatile metabolisms. In that vein, we assessed PHA production by the photosynthetic purple non‐sulfur bacteria (PNSB) Rhodomicrobium vannielii and Rhodomicrobium udaipurense. We show that both species accumulate PHA across photo‐heterotrophic, photo‐hydrogenotrophic, photo‐ferrotrophic, and photo‐electrotrophic growth conditions, with either ammonium chloride (NH4Cl) or dinitrogen gas (N2) as nitrogen sources. Our data indicate that nitrogen source plays a significant role in dictating PHA synthesis, with N2 fixation promoting PHA production during photoheterotrophy and photoelectrotrophy but inhibiting production during photohydrogenotrophy and photoferrotrophy. We observed the highest PHA titres (up to 44.08 mg/L, or 43.61% cell dry weight) when cells were grown photoheterotrophically on sodium butyrate with N2, while production was at its lowest during photoelectrotrophy (as low as 0.04 mg/L, or 0.16% cell dry weight). We also find that photohydrogenotrophically grown cells supplemented with NH4Cl exhibit the highest electron yields – up to 58.89% – while photoheterotrophy demonstrated the lowest (0.27%–1.39%). Finally, we highlight superior electron conversion and PHA production compared to a related PNSB, Rhodopseudomonas palustris TIE‐1. This study illustrates the value of studying non‐model organisms like Rhodomicrobium for sustainable PHA production and indicates future directions for exploring PNSB metabolisms. [ABSTRACT FROM AUTHOR]

Direct interspecies electron transfer (DIET) is essential for maintaining the function and stability of anaerobic microbial consortia. However, only limited natural DIET modes have been identified and DIET engineering remains highly challenging. In this study, an unnatural DIET between Shewanella oneidensis MR‐1 (SO, electron donating partner) and Rhodopseudomonas palustris (RP, electron accepting partner) was artificially established by a facile living cell‐cell click chemistry strategy. By introducing alkyne‐ or azide‐modified monosaccharides onto the cell outer surface of the target species, precise covalent connections between different species in high proximity were realized through a fast click chemistry reaction. Remarkably, upon covalent connection, outer cell surface C‐type cytochromes mediated DIET between SO and RP was achieved and identified, although this was never realized naturally. Moreover, this connection directly shifted the natural H2 mediated interspecies electron transfer (MIET) to DIET between SO and RP, which delivered superior interspecies electron exchange efficiency. Therefore, this work demonstrated a naturally unachievable DIET and an unprecedented MIET shift to DIET accomplished by cell‐cell distance engineering, offering an efficient and versatile solution for DIET engineering, which extends our understanding of DIET and opens up new avenues for DIET exploration and applications. [ABSTRACT FROM AUTHOR]

Sewer concrete structures are vulnerable to acidic corrosion due to the biological oxidation of sulfide in the wastewater to sulfuric acid. The use of photosynthetic bacteria in the coating layer on the sewer concrete is proposed to be an effective approach to prevent such corrosion. Here we report two strains, PN6 and PN7, isolated from a drainage system in Hanoi that were identified as Rhodopseudomonas palustris PN6 and Rhodobacter capsulatus PN7 based on a comparative analysis of the 16S rDNA and pufM gene sequences. Both strains performed versatile metabolic paths, including anoxygenic and microaerophilic phototrophy and aerobic chemotrophy, allowing them to adapt to the fluctuating sewer conditions. Furthermore, they exhibited notable capability of oxidizing sulfide and producing glycocalyx, and therefore were able to prevent concrete corrosion by scavenging sulfide and reducing the production of sulfuric acid, at the same time sealing the tiny cracks on the concrete surface and preventing further attack of the corrosive agents. Two strains grew well at an alkali pH of 9 and formed biofilm extensively, and therefore can be incorporated into porous material vermiculite, allowing them to survive in the coating mortar. The protective effect of coating mortar containing strains PN6 or PN7 singly or in a combination of both incorporated in vermiculite was demonstrated in a laboratory model simulating the sewer environment with an acidic vapor atmosphere. Without bacteria in the coating mortar, the concrete surface suffered severe corrosion with spots of 0.01–0.2 mm in width and up to 4.5 mm in length clustering in rafts of 10–70 mm2 , whereas the concrete surface coated by bacteria-containing mortar was intact to corrosion. The study proposed the possibility of applying purple nonsulfur bacteria (PNSB) to protect sewer concrete, and also prolong the service life of these important structures. Practical Applications: Sewer concrete systems are daily attacked by acidic corrosion established via the biological oxidation of sulfide to sulfuric acid. The repair is generally costly and has difficulties in implementation. The use of PNSB with the capabilities of scavenging H2S and producing exopolysaccharide (EPS) for the development of a coating layer would be a feasible approach to constrain the corrosion process. Suitable strains of PNSB such as the two strains Rhodopseudomonas palustris PN6 and Rhodobacter capsulatus PN7 reported in this study are supposed to be incorporated in a porous material like vermiculite before being added to the coating mortar to better stabilize and adapt to the harsh conditions of the coating layer. These types of PNSB can survive in the coating layer and multiply by utilizing organic carbon and sulfide from wastewater with the production of sulfur (instead of sulfuric acid) and glycocalyx that can instantly seal the tiny corrosion spots and prevent further corrosion attacks. This approach is supposed to be a prevention solution to increase the service durability of sewer concrete systems and reduce the need for repair implementation. [ABSTRACT FROM AUTHOR]

Sea urchin contains physiologically active substances, such as amino acids and unsaturated fatty acids, and an important aquatic organism. Purple sea urchin, one of the common edible sea urchins, is an important aquatic product. In order to supply the vast seafood market, large‐scale aquaculture of sea urchins is very important. The aim of this study was to optimize the rearing of the Anthocidaris crassipina larvae enhancing the nutrition by mixing feed to improve their growth and survival. The survival rate of Chaetoceros muelleri feeding alone is only 40%. If the survival rate is improved through nutrient enrichment, the large‐scale aquaculture of larvae can be promoted. The experiment was divided into two parts. Experiment 1: Two types of commonly used microalgae, Isochrysis galbana tml (I), C. muelleri (C) and two types of probiotics, Rhodopseudomonas palustris (R), and Saccharomyces cerevisiae (S) were used in the. Feeding amounts are 5000, 10,000, and 20,000 cell mL−1, and the control group (N) did not eat. Experiment 2: C. muelleri 20,000 cell mL−1 was mixed with I. galbana tml, R. palustris (R) and S. cerevisiae (S) at 5000 and 10,000 cell mL−1. After the experiment, body length, body width, stomach length, rudiment length, rudiment length, body composition, digestive enzymes and survival rate were measured to evaluate the best feed. The results showed that the mixed feeding of C. muelleri 20,000 cell mL−1 and R. palustris 5000 cell mL−1 can achieve the best development and survival of larval embryos and can promote metamorphosis into juveniles in the shortest time. The research results will be applied to the large‐scale aquaculture of A. crassipina larvae to promote the diversity of aquaculture. [ABSTRACT FROM AUTHOR]

Using microorganisms can develop into a promising strategy for increasing photosynthetic activity and greater accumulation of assimilates in crops. This study aimed to evaluate the effects of Rhodopseudomonas palustris on fruit yield and quality of 'Keitt' mangoes grown under semi-arid environmental conditions. The experiment was carried out simultaneously in two mango orchards in Petrolina, Pernambuco, Brazil. The study comprised a randomized block design with treatments distributed in 7 treatments, 4 replications, and 3 plants per plot. The treatments consisted of different strategies for applying R. palustris. These treatments were T1) control treatment; T2) 1.43 × 107 CFU/plant via fertigation; T3) 2.85 × 107 CFU/plant via fertigation; T4) 4.27 × 107 CFU/plant via fertigation; T5) 5.70 × 107 CFU/plant via fertigation; T6) 1.43 × 107 CFU/plant via fertigation + 1.43 × 107 CFU/plant via leaf spray; T7) 2.85 × 107 CFU/plant via fertigation + 1.43 × 107 CFU/plant via leaf spray. The treatments were a pplied monthly, totaling seven applications. We evaluated fruit yield (M g ha-1), longitudinal diameter, ventral diameter and transverse diameter, fruit mass, pulp firmness, pulp percentage, soluble solids (SS), pH, titratable acidity (TA), SS/TA ratio, and dry pulp mass. R. palustris improved mango yield and fruit quality characteristics regarding longitudinal and transversal diameters and the SS/TA ratio. Mango plants treated with R. palustris at 1.43 × 107 CFU/plant via fertigation (T2) produced 10 Mg ha-1 more than the control group, without loss of fruit quality while considering the European market demand. [ABSTRACT FROM AUTHOR]

Polylactic acid (PLA) is attracting significant interest as a sustainable alternative to conventional plastics. However, its biodegradation rates vary across environments, and its integration into existing recycling infrastructure necessitates the development of complex end-of-life management strategies. Enzymatic depolymerization offers a promising pathway for closed-loop recycling and upcycling of waste plastics by recovering monomeric building blocks. Yet, few enzymes have been identified that exhibit PLA depolymerization efficiency comparable to those known for PET degradation. Here, we report the computational design of an esterase, RPA1511, from Rhodopseudomonas palustris, which exhibits hydrolytic activity against solid PLA but lacks thermal stability. Using a variety of computational enzyme stability design tools, a focused library was constructed for experimental validation. Further accumulation of beneficial mutations resulted in a five-point variant, R5, which showed an 8 °C increase in melting temperature (Tm) and a substantial 11.5-fold increase in relative enzyme activity at optimal temperatures. This variant achieved efficient PLA degradation, converting 85.38% of PDLLA powder into lactate monomers within 72 h at 65 °C, with a 3.3-fold enhancement compared to wild-type RPA1511. Molecular dynamics simulations showed that the V202 W mutation induced structural changes in the substrate binding pocket and potentially formed more productive complexes, while the remaining four mutations improved the variant's thermal stability. This combined approach through computational design yielded an efficient and thermostable PLA depolymerase, potentially facilitating PLA bio-recycling processes. [ABSTRACT FROM AUTHOR]

It has been previously shown that devices based on microbial biofilms can generate hydrovoltaic energy from water evaporation. However, the potential of hydrovoltaic energy as an energy source for microbial growth has remained unexplored. Here, we show that the electroautotrophic bacterium Rhodopseudomonas palustris can directly utilize evaporation-induced hydrovoltaic electrons for growth within biofilms through extracellular electron uptake, with a strong reliance on carbon fixation coupled with nitrate reduction. We obtained similar results with two other electroautotrophic bacterial species. Although the energy conversion efficiency for microbial growth based on hydrovoltaic energy is low compared to other processes such as photosynthesis, we hypothesize that hydrovoltaic energy may potentially contribute to microbial survival and growth in energy-limited environments, given the ubiquity of microbial biofilms and water evaporation conditions. Devices based on microbial biofilms can be used to generate hydrovoltaic energy from water evaporation. Here, Ren et al. show that, in addition, electroautotrophic bacteria can use evaporation-induced hydrovoltaic electrons for growth in biofilms. [ABSTRACT FROM AUTHOR]

The presence of acid sulfate soils is such an obstacle for pineapple cultivation in Vietnam due to their low pH, high toxicity and poor nutrient availability, especially phosphorus (P), which is immobilized by cations in the soils. Therefore, the study occurred to select purple nonsulfur bacteria (PNSB) strains that can solubilize P under toxic and acidic conditions. There were 33 strains that can tolerate the acidic condition, and they were selected and tested for viability and P solubilization under conditions containing Al3+, Fe2+, and Mn2+ toxins. Four strains, including W15, W39, W42 and W48 suffered from growth inhibition by Al3+, Fe2+ and Mn2+ less than the other strains under both microaerobic light and aerobic dark conditions (ML and AD conditions). In addition, there were four strains (W15, W25, W42 and W48) solubilizing Al-P well (21.4-25.2 mg L-1), two strains (W23 and W42) solubilizing Fe-P well (15.9-17.3 mg L-1), and two strains (W17 and W42) solubilizing Ca-P well (23.0-36.4 mg L-1) under both ML and AD conditions. Ultimately, there were five strains selected (W17, W23, W25, W42 and W48) and identified as Rhodopseudomonas palustris strain W17 and W23, Cereibacter sphaeroides strain W23, W42 and W48 based on the 16S rRNA technique. The selected strains also produced ALA, EPS and siderophores at 1.31-2.19 mg L-1, 0.78-1.89 mg L-1, and 16.2-55.6%, respectively. Therefore, these strains were promising in providing nutrients for pineapples in the form of biofertilizer. [ABSTRACT FROM AUTHOR]

Photosynthetic diazotrophs expressing iron-only (Fe-only) nitrogenase can be developed into a promising biofertilizer, as it is independent on the molybdenum availability in the soil. However, the expression of Fe-only nitrogenase in diazotrophs is repressed by the fixed nitrogen of the soil, limiting the efficiency of nitrogen fixation in farmland with low ammonium concentrations that are inadequate for sustainable crop growth. Here, we succeeded in constitutively expressing the Fe-only nitrogenase even in the presence of ammonium by controlling the transcription of Fe-only nitrogenase gene cluster (anfHDGK) with the transcriptional activator of Mo nitrogenase (NifA*) in several different ways, indicating that the engineered NifA* strains can be used as promising chassis cells for efficient expression of different types of nitrogenases. When applied as a biofertilizer, the engineered Rhodopseudomonas palustris effectively stimulated rice growth, contributing to the reduced use of chemical fertilizer and the development of sustainable agriculture. [ABSTRACT FROM AUTHOR]

Using beneficial microorganisms, such as purple non-sulfur bacteria (PNSB), has shown enormous potential for improving plant growth and agricultural production. However, the full extent of their benefits and interactions with agricultural practices is yet to be fully understood. The present study aimed to investigate the use of PNSB in crop rotation practice, focusing on its impact on rice growth and yield. The experiment was conducted over two rice cropping seasons, with djulis grown between the rice as a rotation crop. The study shows that PNSB treatment increased the concentration of 5-aminolevulinic acid (5-ALA) in plants, indicating enhanced photosynthesis. Moreover, when combined with crop rotation, PNSB remarkably improved soil fertility. These combined benefits resulted in substantial increases in tiller numbers (163%), leaf chlorophyll content (13%), and lodging resistance (66%), compared to the untreated plants. The combined treatment also resulted in higher productive tillers per hill (112%), average grain per hill (65%), and grain fertility (26%). This led to increased grain yield (65%), shoot dry weight (15%), and harvest index (37%). The findings clearly suggest that the incorporation of PNSB in crop rotation strategies can significantly augment the growth and yield of rice crops. These insights, pivotal for sustainable rice cultivation, hold the potential to simultaneously tackle the pressing issues of global food security and climate change. [ABSTRACT FROM AUTHOR]

Rhodopseudomonas palustris, is a purple non-sulphur bacterium with properties of extraordinary metabolic versatility, carbon source diversity and metabolite diversity. Due to its biodetoxification and biodegradation properties, R. palustris has been traditionally applied in wastewater treatment and bioremediation, and also in agriculture. This study aimed to isolate and identify R. palustris from waste dump site in Minna, Nigeria, using conventional and molecular techniques. Soil samples were collected at 3 cm depth from different points at waste dump sites in Minna, Niger State, Nigeria. Inoculation was made on Nutrient agar plates and incubated at 30 °C under 60 W incandescent light for 7days. The suspected bacterial isolate, based on cultural and morphological characteristics as well as biochemical reactions was subjected to molecular ribotyping. A PCR product of approximately 789 bp DNA maker was detected by agarose gel electrophoresis using 1500 bp Lamda maker. The DNA fragments of the isolates were obtained from DNA sequencing and were deposited in the NCBI-GenBank database. Based BLASTn search in GenBank using the fragments as the query, showed that the 16S rDNA of EG-4 share 99% sequence identity with Rhodopseudomonas palustris. Results of this study indicate the presence of R. palustris in waste dump site in Minna. [ABSTRACT FROM AUTHOR]

Small slaughterhouses generate biowaste, which for economic reasons, is generally destined for composting. Inoculating appropriate microorganisms can improve biodegradation efficiency and mitigate odor generation during the composting process and can give rise to composts with neutral or pleasant odors. Therefore, the aim of this study was to compare the odor intensity reduction of compost generated with and without a formulated inoculum (Saccharomyces cerevisiae, Bacillus subtilis, and Rhodopseudomonas palustris). A set of experimental data was collected and analyzed according to the German "Verein Deutscher Ingenieure" odor protocol. The results showed that adding microorganisms was effective in reducing unpleasant odors in all three composts generated from swine, cattle, and poultry slaughterhouse by-products during both summer and winter seasons. Additionally, soil odor was predominant in composts that were inoculated in the two tested seasons (i.e., summer and winter). On the other hand, composts without inoculation had odors similar to peat for swine compost, ammonia for cattle compost, and manure for poultry compost, regardless of the season tested. Overall, composting process with appropriate inoculum can help in the correct disposal of slaughterhouse wastes by transforming organic matter into composts, which can have economic and environmental value as a soil conditioner and/or fertilizer. [ABSTRACT FROM AUTHOR]

The flavodoxin of Rhodopseudomonas palustris CGA009 (Rp9Fld) supplies highly reducing equivalents to crucial enzymes such as hydrogenase, especially when the organism is iron-restricted. By acquiring those electrons from photodriven electron flow via the bifurcating electron transfer flavoprotein, Rp9Fld provides solar power to vital metabolic processes. To understand Rp9Fld's ability to work with diverse partners, we solved its crystal structure. We observed the canonical flavodoxin (Fld) fold and features common to other long-chain Flds but not all the surface loops thought to recognize partner proteins. Moreover, some of the loops display alternative structures and dynamics. To advance studies of protein-- protein associations and conformational consequences, we assigned the 19F NMR signals of all five tyrosines (Tyrs). Our electrochemical measurements show that incorporation of 3-19F-Tyr in place of Tyr has only a modest effect on Rp9Fld's redox properties even though Tyrs flank the flavin on both sides. Meanwhile, the 19F probes demonstrate the expected paramagnetic effect, with signals from nearby Tyrs becoming broadened beyond detection when the flavin semiquinone is formed. However, the temperature dependencies of chemical shifts and linewidths reveal dynamics affecting loops close to the flavin and regions that bind to partners in a variety of systems. These coincide with patterns of amino acid type conservation but not retention of specific residues, arguing against detailed specificity with respect to partners. We propose that the loops surrounding the flavin adopt altered conformations upon binding to partners and may even participate actively in electron transfer. [ABSTRACT FROM AUTHOR]

In the present study, three purple non sulphur bacterial strains were isolated from water and soil samples and were characterised. The three bacterial strains were identified as Rhodopsuedomonas palustris RM01, Rhodopsuedomonas rhenobacensis RM02 and Rhodopsuedomonas palustris RM03 strains. All the three Rhodopseudomonas species strains were nonmotile and the absorption spectral characters revealed the presence of bacteriochlorophyll "a" by ultra-visible spectroscopy. Rhodopseudomonas palustris RM01 showed an absorption maxima at 673, 806 and 865 nm) and the type of carotenoids as spirilloxanthin (absorption maxima at 389, 474, 502, 592 and 530 nm), Rhodopseudomonas rhenobacensis RM02 absorption maxima have seen at 806 and 867 nm and the type of carotenoids as spirilloxanthin (absorption maxima at 382, 473, 503, 591 and 530 nm) and Rhodopseudomonas palustris RM03 absorption maxima was at 759, 805 and 874 nm) and the type of carotenoids as spirilloxanthin (absorption maxima at 376, 492 and 591 nm). RM01, RM02, and RM03 strains were shown a dry biomass yield was 12.1grams, 16.8grams and 13.6grams dry weight per litre, respectively. All the isolated PNSB strains could grow in a range of 6-7 pH tested. Sequence data of the strain was deposited in NCBI (National Centre for Biotechnology Information). These three bacteria Rhodopseudomonas palustris RM01, Rhodopseudomonas. Rhenobacensis RM02 and Rhodopseudomonas palustris RM03 have optimal growth at 28°C & 30°C respectively. Further morphological characterization of these three strains were carried out on the basis of microscopic observations, SEM studies, colour of cell suspensions, absorption spectral characters, organic and inorganic substrate utilization, vitamin requirement, temperature growth and biomass production and 16S rRNA gene sequencing analysis. They were identified and named as Rhodopseudomonas palustris RM01, Rhodopseudomonas rhenobacensis RM02 and Rhodopseudomonas palustris RM03. These were further screened for biomass production. [ABSTRACT FROM AUTHOR]

Physiological and metabolic behavior of photoheterotrophic mixed cultures (PHMCs), monocultures of Rhodopseudomonas palustris , Clostridium pasteurianum and Syntrophomonas wolfei and a designed microbial consortium (DMC), consisting of these microorganisms that emulates natural consortia were studied. Growing and photoheterotrophic nongrowing conditions to simulate the use of dark fermentative effluents were used. Under growing conditions, C. pasteurianum showed higher bioH 2 production (8.5 mmol) and molar bioH 2 yield (21 mmoLH 2 /gCOD), while R. palustris did not produce this gas. Under nongrowing conditions, DMC reached the highest bioH 2 production (10 mmol) and bioH 2 yield (78.6 mmoLH 2 /gCOD) together with Poly-hydroxy-alkanoates (PHA), followed for PHMC-C2 (7.5; 59.6) and the monocultures. Higher bioH 2 and PHA production of the PHMC and the DMC suggest that these conditions promote the use of nonconventional energy pathways, and interactions among microbial populations that allow for the survival and sustain bioH 2 production. This study forms the basis for more in-depth studies of the metabolic behavior of photosynthetic natural and designed cultures. [Display omitted] • Metabolic behavior of natural and designed photoheterotrophic cultures was evaluated. • Nongrowing conditions promote the highest bioH 2 production in microbial consortia. • Microbial interactions allow for the survival and sustain bioH 2 production. • BioH 2 and PHA production are involved in the metabolic energy conservation. • Feasibility of design a microbial community for high bioH 2 production was demonstrated. [ABSTRACT FROM AUTHOR]

Rhodopseudomonas palustris TIE‐1 grows photoautotrophically with Fe(II) as an electron donor and photoheterotrophically with a variety of organic substrates. However, it is unclear whether R. palustris TIE‐1 conducts Fe(II) oxidation in conditions where organic substrates and Fe(II) are available simultaneously. In addition, the effect of organic co‐substrates on Fe(II) oxidation rates or the identity of Fe(III) minerals formed is unknown. We incubated R. palustris TIE‐1 with 2 mM Fe(II), amended with 0.6 mM organic co‐substrate, and in the presence/absence of CO2. We found that in the absence of CO2, only the organic co‐substrates acetate, lactate and pyruvate, but not Fe(II), were consumed. When CO2 was present, Fe(II) and all organic substrates were consumed. Acetate, butyrate and pyruvate were consumed before Fe(II) oxidation commenced, whereas lactate and glucose were consumed at the same time as Fe(II) oxidation proceeded. Lactate, pyruvate and glucose increased the Fe(II) oxidation rate significantly (by up to threefold in the case of lactate). 57Fe Mössbauer spectroscopy revealed that short‐range ordered Fe(III) oxyhydroxides were formed under all conditions. This study demonstrates phototrophic Fe(II) oxidation proceeds even in the presence of organic compounds, and that the simultaneous oxidation of organic substrates can stimulate Fe(II) oxidation. [ABSTRACT FROM AUTHOR]

In the Mekong Delta Vietnam, rice is heavily affected by Al3+ and Fe2+ ions appearing in local acid sulfate soils (AAS). Therefore, the current study was carried out to assess the efficacy of a liquid biofertilizer (LB) containing nitrogen-fixing and phosphorus-solubilizing bacterial strains of Rhodopseudomonas spp. on remediation of soil characteristics and improvements of rice uptakes, growth, and yield. The experiment was designed in a randomized block design with nine treatments and four replications in an ASS. The results have shown that the LB application could contribute to the remediation of soil properties, including an increase in concentrations of NH4+ by 12.9%–19.4%, soluble P by 25.7%–42.6%, total N uptake by 40.7–64.0 kg ha−1 and total P uptake by 5.60–12.6 kg ha−1, and a decrease in concentrations of toxins, such as Al3+ by 12.1%–19.7% and Fe2+ by 16.6%–19.0%, compared to the treatment with the farmer-based fertilization. Thereby, grain yield was improved by 31.9%–32.2% with the LB versus the treatments without the bacteria and by 9.5%–11.1% compared to the commercial biofertilizer treatments. The application of LB reduced 25% N and 50% P of the recommendation versus the farmers' fertilization and improved performance of rice growth and yield cultivated on ASS which suffered from Al3+ and Fe2+ ions. The current study has introduced the potential of the Rhodopseudomonas palustris TLS06, VNW02, VNW64, and VNS89 strains in performance as a bioremediator and a biofertilizer. The strains have shown their ability to recover acid sulfate soils, which had damaged the yield of rice plants due to high concentrations of Al3+ and Fe2+ ions. The work has delivered a biological approach to improve acid sulfate soil fertility and rice productivity in Vietnam and in other parts of the world, which have similar conditions, to achieve sustainable agriculture and food security. [ABSTRACT FROM AUTHOR]

Abstract Background Pickled mustard, the largest cultivated vegetable in China, generates substantial waste annually, leading to significant environmental pollution due to challenges in timely disposal, leading to decomposition and sewage issues. Consequently, the imperative to address this concern centers on the reduction and comprehensive resource utilization of raw mustard waste (RMW). To achieve complete and quantitative resource utilization of RMW, this study employs novel technology integration for optimizing its higher-value applications. Results Initially, subcritical hydrothermal technology was applied for rapid decomposition, with subsequent ammonia nitrogen removal via zeolite. Thereafter, photosynthetic bacteria, Rhodopseudomonas palustris, were employed to maximize hydrogen and methane gas production using various fermentation enhancement agents. Subsequent solid-liquid separation yielded liquid fertilizer from the fermented liquid and soil amendment from solid fermentation remnants. Results indicate that the highest glucose yield (29.6 ± 0.14) was achieved at 165–173℃, with a total sugar content of 50.2 g/L and 64% glucose proportion. Optimal ammonia nitrogen removal occurred with 8 g/L zeolite and strain stable growth at 32℃, with the highest OD600 reaching 2.7. Several fermentation promoters, including FeSO4, Neutral red, Na2S, flavin mononucleotide, Nickel titanate, Nickel oxide, and Mixture C, were evaluated for hydrogen production. Notably, Mixture C resulted in the maximum hydrogen production (756 mL), a production rate of 14 mL/h, and a 5-day stable hydrogen production period. Composting experiments enhanced humic acid content and organic matter (OM) by 17% and 15%, respectively. Conclusions This innovative technology not only expedites RMW treatment and hydrogen yield but also substantially enriches soil fertility. Consequently, it offers a novel approach for low-carbon, zero-pollution RMW management. The study’s double outcomes extend to large-scale RMW treatment based on the aim of full quantitative resource utilization of RMW. Our method provides a valuable reference for waste management in similar perishable vegetable plantations.

The research experimentally investigated biohydrogen production with a light intensity of 4500 lux using indigenous bacteria in DEPOME. The study was conducted in three stages: identified indigenous bacteria through next-generation sequencing (NGS) DNA, analyzed DEPOME characteristics, and produced biohydrogen. Biohydrogen production was carried out under two initial substrate pH conditions: neutral (pH 7) and natural pH substrate (4.9–5.4) for 88 h at a controlled temperature of 30 °C, with measurements of gas production and observations of changes in dissolved oxygen (DO), oxidation-reduction potential (ORP), and substrate pH taken at 4-h intervals. Rhodopseudomonas palustris bacteria was identified as indigenous bacteria for photo-fermentation in POME. The yield, gas production rate, and light conversion efficiency (LCE) were found to be 147.65 mg-H 2 /L-Depome, 1.68 mg-H 2 /L-Depome/h, and 11.75 % under the initial pH neutralization treatment, while without initial pH treatment, the values were 78.5 mg-H 2 /L-Depome, 0.89 mg-H 2 /L-Depome/h, and 6.25 %. [Display omitted] • Rhodopseudomonas palustris was found as indigenous bacteria on POME. • pH is one of the most influential factors for good bacterial growth. • Changes in ORP and pH during the process have an impact on biohydrogen yields. • DEPOME has good potential as a photo-fermentation substrate. [ABSTRACT FROM AUTHOR]

Halogenated aromatic compounds are used in a variety of industrial applications but can be harmful to humans and animals when released into the environment. Microorganisms that degrade halogenated aromatic compounds anaerobically have been isolated but the evolutionary path that they may have taken to acquire this ability is not well understood. A strain of the purple nonsulfur bacterium, Rhodopseudomonas palustris, RCB100, can use 3-chlorobenzoate (3-CBA) as a carbon source whereas a closely related strain, CGA009, cannot. To reconstruct the evolutionary events that enabled RCB100 to degrade 3-CBA, we isolated an evolved strain derived from CGA009 capable of growing on 3-CBA. Comparative whole-genome sequencing of the evolved strain and RCB100 revealed both strains contained large deletions encompassing badM, a transcriptional repressor of genes for anaerobic benzoate degradation. It was previously shown that in strain RCB100, a single nucleotide change in an alicyclic acid coenzyme A ligase gene, named aliA, gives rise to a variant AliA enzyme that has high activity with 3-CBA. When the RCB100 aliA allele and a deletion in badM were introduced into R. palustris CGA009, the resulting strain grew on 3-CBA at a similar rate as RCB100. This work provides an example of pathway evolution in which regulatory constraints were overcome to enable the selection of a variant of a promiscuous enzyme with enhanced substrate specificity. [ABSTRACT FROM AUTHOR]

Photo-fermentation is an efficient hydrogen production pathway in which purple non-sulfur bacteria (PNSB) play an active role and produce hydrogen as a part of their metabolism under optimal conditions. These bacteria work under the influence of light to advance their metabolism and use various substrates, such as simple sugars and volatile fatty acids, to produce hydrogen. This article presents a comparative review of several bacterial strains that have been efficiently used to produce hydrogen by photo-fermentation under different optimized conditions, including the substrate, its concentration, type and capacity of the bioreactor, light sources and intensities, and process conditions to achieve the maximum biohydrogen production rate. The analysis showed that the Rhodopseudomonas palustris is the main bacterium used for hydrogen production, with a maximum hydrogen production rate of 3.2 mM/h using 27.8 mM of glucose in a 165 mL serum bottle and 3.23 mM/h using 50 mM of glycerol at pH 7, followed by Rhodobacter sphaeroides, which gave a hydrogen production rate as high as 8.7 mM/h, using 40 mM of lactic acid, pH 7, and 30 °C temperature in a single-walled glass bioreactor. However, it is not preferred over R. palustris due to its versatile metabolism and ability to use an alternative mode if the conditions are not carefully adjusted, which can be a problem in hydrogen production. [ABSTRACT FROM AUTHOR]

Background: Pickled mustard, the largest cultivated vegetable in China, generates substantial waste annually, leading to significant environmental pollution due to challenges in timely disposal, leading to decomposition and sewage issues. Consequently, the imperative to address this concern centers on the reduction and comprehensive resource utilization of raw mustard waste (RMW). To achieve complete and quantitative resource utilization of RMW, this study employs novel technology integration for optimizing its higher-value applications. Results: Initially, subcritical hydrothermal technology was applied for rapid decomposition, with subsequent ammonia nitrogen removal via zeolite. Thereafter, photosynthetic bacteria, Rhodopseudomonas palustris, were employed to maximize hydrogen and methane gas production using various fermentation enhancement agents. Subsequent solid-liquid separation yielded liquid fertilizer from the fermented liquid and soil amendment from solid fermentation remnants. Results indicate that the highest glucose yield (29.6 ± 0.14) was achieved at 165–173℃, with a total sugar content of 50.2 g/L and 64% glucose proportion. Optimal ammonia nitrogen removal occurred with 8 g/L zeolite and strain stable growth at 32℃, with the highest OD600 reaching 2.7. Several fermentation promoters, including FeSO4, Neutral red, Na2S, flavin mononucleotide, Nickel titanate, Nickel oxide, and Mixture C, were evaluated for hydrogen production. Notably, Mixture C resulted in the maximum hydrogen production (756 mL), a production rate of 14 mL/h, and a 5-day stable hydrogen production period. Composting experiments enhanced humic acid content and organic matter (OM) by 17% and 15%, respectively. Conclusions: This innovative technology not only expedites RMW treatment and hydrogen yield but also substantially enriches soil fertility. Consequently, it offers a novel approach for low-carbon, zero-pollution RMW management. The study's double outcomes extend to large-scale RMW treatment based on the aim of full quantitative resource utilization of RMW. Our method provides a valuable reference for waste management in similar perishable vegetable plantations. [ABSTRACT FROM AUTHOR]

Previous research has shown that the pathogenicity and appressorium development of Magnaporthe oryzae can be inhibited by the ATP synthase subunit beta (Atp2) present in the photosynthetic bacterium Rhodopseudomonas palustris. In the present study, transgenic plants overexpressing the ATP2 gene were generated via genetic transformation in the Zhonghua11 (ZH11) genetic background. We compared the blast resistance and immune response of ATP2-overexpressing lines and wild-type plants. The expression of the Atp2 protein and the physiology, biochemistry, and growth traits of the mutant plants were also examined. The results showed that, compared with the wild-type plant ZH11, transgenic rice plants heterologously expressing ATP2 had no significant defects in agronomic traits, but the disease lesions caused by the rice blast fungus were significantly reduced. When infected by the rice blast fungus, the transgenic rice plants exhibited stronger antioxidant enzyme activity and a greater ratio of chlorophyll a to chlorophyll b. Furthermore, the immune response was triggered stronger in transgenic rice, especially the increase in reactive oxygen species (ROS), was more strongly triggered in plants. In summary, the expression of ATP2 as an antifungal protein in rice could improve the ability of rice to resist rice blast. [ABSTRACT FROM AUTHOR]

This study aimed to evaluate the effects of purple non-sulfur bacteria (PNSB) biofertilizers on soil properties, nitrogen (N) and phosphorus (P) uptakes, growth, and grain yield of sesame cultivated on salt-affected soil. N2-fixing and P-solubilizing bacteria used as biofertilizers were PNSB Rhodopseudomonas palustris VNW64, VNS89, TLS06 and VNS02, and endophytic bacteria (EB) Enterobacter cloacae X4 and Burkholderia acidipaludis X5. The experiment was conducted in a completely randomized block design, with 9 treatments (i) 100% N and 100% P of recommended fertilizer formula (RFF), (ii) 75% N and 50% P, (iii) 50% N and 50% P, (iv) treatment ii plus PNSB biofertilizers, (v) treatment iii plus PNSB biofertilizers, (vi) treatment ii plus EB biofertilizers, (vii) treatment iii plus EB biofertilizers, (viii) PNSB biofertilizers only, and (ix) carriers only, a rice straw and hush ash mixture. Results revealed that application of PNSB biofertilizers significantly improved soil fertility, nutrient uptakes, and yield as compared to treatments that used chemical fertilizers with or without EB biofertilizers at the same amount of N and P fertilizers applied. The use of 75% N and 50% P of RFF plus PNSB biofertilizers enhanced soil pHH2O, NH4+, soluble P, and N, P uptakes in sesame as compared to 100% N and 100% P of RFF. PNSB biofertilizers not only reduced 50% N and 50% P of RFF, but also maintained yield as compared to the treatment using 100% N, P of RFF (6.06 and 6.09 g pot−1, respectively) and limited Na uptake in sesame and Na+ concentration in the soil. [ABSTRACT FROM AUTHOR]

The present study was aimed to evaluate the effects of nitrogen (N) fixing Rhodopseudomonas palustris strains, VNW64, VNS89, TLS06 and VNS02 on soil fertility, growth and yield of hybrid maize cultivated on in-dyke alluvial soil (IDAS). The pot experiment followed a completely randomized block design with 10 treatments, 4 replicates for each treatment. The treatments comprised of (i) fertilization with 100% N following recommended fertilizer formula (RFF), (ii) fertilization with 85% N, (iii) fertilization with 70% N, (iv) fertilization with 55% N, (v) treatment i plus a mixture of four purple nonsulfur bacteria (MFPNSB), (vi) treatment ii plus MFPNSB, (vii) treatment iii plus MFPNSB, (viii) treatment iv plus MFPNSB, (ix) no chemical fertilization, and (x) Treatment ix plus MFPNSB. The result indicated that treatments supplied with MFPNSB enhanced soil properties, including soil pHWater, NH4+ content and total N uptake, in comparison with no supplemented bacteria, 6.11–6.15, 16.4–17.7 mg NH4+ kg-1 and 1.43–5.02 mg N pot-1 in comparison with 5.74–5.99, 11.3–12.7 mg NH4+ kg-1 and 0.82–3.11 mg N pot-1, respectively, for hybrid maize cultivated on IDAS. Inoculation of MFPNSB on maize seeds contributed to reduce 45% N of RFF, but still caused no decline in the grain yield of maize. At 100% N of RFF, the treatment supplemented MFPNSB possessed a grain yield of 20.2% higher than the treatment without supplemented MFPNSB. Additionally, the treatment fertilized with 85% N of RFF plus MFPNSB, the maize grain yield was increased by 12.5% compared to the treatment fertilized with 100% N of RFF. [ABSTRACT FROM AUTHOR]

Denitrification is a form of anaerobic respiration wherein nitrate (NO3 -) is sequentially reduced via nitrite (NO2 -), nitric oxide, and nitrous oxide (N2O) to dinitrogen gas (N2) by four reductase enzymes. Partial denitrifying bacteria possess only one or some of these four reductases and use them as independent respiratory modules. However, it is unclear if partial denitrifiers sense and respond to denitrification intermediates outside of their reductase repertoire. Here, we tested the denitrifying capabilities of two purple nonsulfur bacteria, Rhodopseudomonas palustris CGA0092 and Rhodobacter capsulatus SB1003. Each had denitrifying capabilities that matched their genome annotation; CGA0092 reduced NO2 - to N2, and SB1003 reduced N2O to N2. For each bacterium, N2O reduction could be used both for electron balance during growth on electron-rich organic compounds in light and for energy transformation via respiration in darkness. However, N2O reduction required supplementation with a denitri fication intermediate, including those for which there was no associated denitrification enzyme. For CGA0092, NO3 - served as a stable, non-catalyzable molecule that was sufficient to activate N2O reduction. Using a β-galactosidase reporter, we found that NO3 - acted, at least in part, by stimulating N2O reductase gene expression. In SB1003, NO2 - but not NO3 - activated N2O reduction, but NO2 - was slowly removed, likely by a promiscuous enzyme activity. Our findings reveal that partial denitrifiers can still be subject to regulation by denitrification intermediates that they cannot use. [ABSTRACT FROM AUTHOR]

The study was aimed to evaluate the efficacy of supplying a mixture of four phosphorus (P)-solubilizing purple nonsulfur bacteria strains, Rhodopseudomonas palustris VNW64, VNS89, TLS06, and VNW02 (P-solubilizing purple nonsulfur bacteria (PS-PNSB)) on soil properties, P uptake, growth, and yield of canary melon (Cucumis melo L.). The experiment consisted of eight treatments, including 100% P (150 kg P2O5 ha−1) as recommended, 75% P, 50% P (75 kg P2O5 ha−1), and no fertilizers, and these treatments with adding PS-PNSB mixture. The results showed that supplying the PS-PNSB mixture had improved the soil pH and the available P content. Moreover, fertilizing 100% P with the mixture of the four PS-PNSB strains resulted in the greatest P uptake (7.88 kg P ha−1). However, interestingly, when supplying 75% P with the PS-PNSB mixture, the P uptake was 6.11 kg P ha−1 and was statistically equal to the 100% P treatment (5.87 kg P ha−1). This could be found in other parameters. Therefore, supplying the PS-PNSB mixture can be claimed to reduce 25% P, but still maintain plant height, fruit length, fruit perimeter, and yield of canary. In addition, supplying the PS-PNSB mixture contributed to a 5.26–9.42% increase in the canary melon yield among P fertilizer rates. Based on the aforementioned results, the PS-PNSB mixture in the current study should be further commercialized and transferred for farmers' use to enhance the yield of canary melons and reduce the rate of chemical fertilizers for the ultimate goal of sustainable agriculture. [ABSTRACT FROM AUTHOR]

Rhodopseudomonas palustris CGA009 is a Gram-negative, purple non-sulfur, metabolically diverse bacterium with wide-ranging habitats. The extraordinary ability of R. palustris to decompose a variety of raw materials and convert them into high-value products makes it an attractive host for biotechnology and industrial applications. However, being a freshwater bacterium R. palustris has limited application in highly-saline environments. Therefore, it is of great significance to obtain the salt-tolerant strain of R. palustris and understand its tolerance mechanism. In this study, R. palustris CGA009 was successfully evolved into eight salt-tolerant strains using an adaptive laboratory evolution technique. RPAS-11 (R. palustris anti-salt strain 11) was selected as the best salt-tolerant strain and was used in further studies to explore the salt-tolerance mechanism. The expression of most genes associated with the carotenoid synthesis in RPAS11 increased significantly under high concentration of salt stress, suggesting that carotenoid synthesis is one of the reasons for the salt tolerance of RPAS-11. Gene overexpression and knockout experiments were performed to get clear about the role of carotenoids in salt stress tolerance. RPAS-11-IDI, the mutant with overexpression of IDI (Isopentenyl diphosphate isomerase) exhibited enhanced salt tolerance, whereas the knockout mutant CGA009-∆crtI showed a decline in salt tolerance. In addition, the results indicated that rhodopin, a carotenoid compound, was the key pigment responsible for the salt tolerance in R. palustris. Furthermore, the production of lycopene, a widely-used carotenoid, was also increased. Taken together, our research helps to deepen the understanding of the salt tolerance mechanism of R. palustris and also widens the application of R. palustris in highly-saline environments. [ABSTRACT FROM AUTHOR]

This study addresses the challenge of mitigating ammonia and greenhouse gas (GHG) emissions from stored pig slurry using chemical and biological additives. The research employs dynamic chambers to evaluate the effectiveness of these additives. Chemical agents (sulfuric acid) and biological additives (DAB bacteria) containing specific microbial strains are tested (a mixture of Rhodopseudomonas palustris, Bacillus subtilis, Bacillus amyloliquefaciens, Bacillus licheniformis, Nitrosomona europea, Nictobacter winogradaskyi, and nutritional substrate). Controlled experiments simulate storage conditions and measure emissions of ammonia, methane, and carbon dioxide. Through statistical analysis of the results, this study evaluates the additives' impact on emission reduction. Sulfuric acid demonstrated a reduction of 92% in CH4, 99% in CO2, and 99% in NH3 emissions. In contrast, the biological additives showed a lesser impact on CH4, with an 8% reduction, but more substantial reductions of 71% for CO2 and 77% for NH3.These results shed light on the feasibility of employing these additives to mitigate environmental impacts in pig slurry management and contribute to sustainable livestock practices by proposing strategies to reduce the ecological consequences of intensive animal farming. [ABSTRACT FROM AUTHOR]

Abstract Background Whole-cell biocatalysis has been exploited to convert a variety of substrates into high-value bulk or chiral fine chemicals. However, the traditional whole-cell biocatalysis typically utilizes the heterotrophic microbes as the biocatalyst, which requires carbohydrates to power the cofactor (ATP, NAD (P)H) regeneration. Results In this study, we sought to harness purple non-sulfur photosynthetic bacterium (PNSB) as the biocatalyst to achieve light-driven cofactor regeneration for cascade biocatalysis. We substantially improved the performance of Rhodopseudomonas palustris-based biocatalysis using a highly active and conditional expression system, blocking the side-reactions, controlling the feeding strategy, and attenuating the light shading effect. Under light-anaerobic conditions, we found that 50 mM ferulic acid could be completely converted to vanillyl alcohol using the recombinant strain with 100% efficiency, and > 99.9% conversion of 50 mM p-coumaric acid to p-hydroxybenzyl alcohol was similarly achieved. Moreover, we examined the isoprenol utilization pathway for pinene synthesis and 92% conversion of 30 mM isoprenol to pinene was obtained. Conclusions Taken together, these results suggested that R. palustris could be a promising host for light-powered biotransformation, which offers an efficient approach for synthesizing value-added chemicals in a green and sustainable manner. Graphical Abstract

The aim of the experiment was to screen and expand the cultivation of salt-tolerant and low-temperature water-regulating photosynthetic bacteria, and provide reference for the industrial production and application of photosynthetic bacteria. Photosynthetic bacteria were isolated from environmental samples, screened by low temperature test of salt tolerance and nitrite reduction ability, and screened by response surface optimization. The results showed that the nitrite degradation rate of DBNRh06 could reach 65% under both light and dark conditions for 48 h, OD660 nm could reach 0.7 under salinity of 35, and the nitrite degradation rate could still reach 50% at 15 ℃ and 120 h. The optimal medium formula of DBNRh06 was ammonium oxalate 2 g/L, sodium acetate 1.5 g/L and yeast powder 1.5 g/L. Using the optimal medium formula, the OD660 nm of DBNRh06 was 0.877, which was very close to the predicted maximum value of 0.860, after being cultured at 30 ℃ and 1 000~2 000 lx for 96 h. The study indicates that a strain of Rhodopseudomonas palustris with good salinity tolerance and low temperature can still reduce nitrite is screened, which has a foundation for the practical application of photosynthetic bacteria in aquaculture industry. [ABSTRACT FROM AUTHOR]

Fluorine forms the strongest single bond to carbon with the highest bond dissociation energy among natural products. However, fluoroacetate dehalogenases (FADs) have been shown to hydrolyze this bond in fluoroacetate under mild reaction conditions. Furthermore, two recent studies demonstrated that the FAD RPA1163 from Rhodopseudomonas palustris can also accept bulkier substrates. In this study, we explored the substrate promiscuity of microbial FADs and their ability to defluorinate polyfluorinated organic acids. Enzymatic screening of eight purified dehalogenases with reported fluoroacetate defluorination activity revealed significant hydrolytic activity against difluoroacetate in three proteins. Product analysis using liquid chromatography‐mass spectrometry identified glyoxylic acid as the final product of enzymatic DFA defluorination. The crystal structures of DAR3835 from Dechloromonas aromatica and NOS0089 from Nostoc sp. were determined in the apo‐state along with the DAR3835 H274N glycolyl intermediate. Structure‐based site‐directed mutagenesis of DAR3835 demonstrated a key role for the catalytic triad and other active site residues in the defluorination of both fluoroacetate and difluoroacetate. Computational analysis of the dimer structures of DAR3835, NOS0089, and RPA1163 indicated the presence of one substrate access tunnel in each protomer. Moreover, protein‐ligand docking simulations suggested similar catalytic mechanisms for the defluorination of both fluoroacetate and difluoroacetate, with difluoroacetate being defluorinated via two consecutive defluorination reactions producing glyoxylate as the final product. Thus, our findings provide molecular insights into substrate promiscuity and catalytic mechanism of FADs, which are promising biocatalysts for applications in synthetic chemistry and bioremediation of fluorochemicals. [ABSTRACT FROM AUTHOR]

The extraordinary metabolic flexibility of anoxygenic phototrophic purple non-sulfur bacteria (PNSB) has been exploited in the development of various biotechnological applications, such as wastewater treatment, biohydrogen production, improvement of soil fertility and plant growth, and recovery of high-value compounds. These versatile microorganisms can also be employed for the efficient bioremediation of hazardous inorganic and organic pollutants from contaminated environments. Certain members of PNSB, especially strains of Rhodobacter sphaeroides and Rhodopseudomonas palustris, exhibit efficient remediation of several toxic and carcinogenic heavy metals and metalloids, such as arsenic, cadmium, chromium, and lead. PNSB are also known to utilize diverse biomass-derived lignocellulosic organic compounds and xenobiotics. Although biodegradation of some substituted aromatic compounds by PNSB has been established, available information on the involvement of PNSB in the biodegradation of toxic organic pollutants is limited. In this review, we present advancements in the field of PNSB-based bioremediation of heavy metals and organic pollutants. Furthermore, we highlight that the potential role of PNSB as a promising bioremediation tool remains largely unexplored. Thus, this review emphasizes the necessity of investing extensive research efforts in the development of PNSB-based bioremediation technology. [ABSTRACT FROM AUTHOR]

Key points The thermosiphon photobioreactor can operate under diurnal light cycles. Diurnal light cycles reduce hydrogen productivity of R. palustris. Diurnal light cycles have little to no effect on the growth of R palustris.

The purple non-sulfur bacterium Rhodopseudomonas palustris is recognized as a critical microorganism in the nitrogen and carbon cycle and one of the most common members in wastewater treatment communities. This bacterium is metabolically extremely versatile. It is capable of heterotrophic growth under aerobic and anaerobic conditions, but also able to grow photoautotrophically as well as mixotrophically. Therefore R. palustris can adapt to multiple environments and establish commensal relationships with other organisms, expressing various enzymes supporting degradation of amino acids, carbohydrates, nucleotides, and complex polymers. Moreover, R. palustris can degrade a wide range of pollutants under anaerobic conditions, e.g., aromatic compounds such as benzoate and caffeate, enabling it to thrive in chemically contaminated environments. However, many metabolic mechanisms employed by R. palustris to breakdown and assimilate different carbon and nitrogen sources under chemoheterotrophic or photoheterotrophic conditions remain unknown. Systems biology approaches, such as metabolic modeling, have been employed extensively to unravel complex mechanisms of metabolism. Previously, metabolic models have been reconstructed to study selected capabilities of R. palustris under limited experimental conditions. Here, we developed a comprehensive metabolic model (M-model) for R. palustris Bis A53 (iDT1294) consisting of 2,721 reactions, 2,123 metabolites, and comprising 1,294 genes. We validated the model using high-throughput phenotypic, physiological, and kinetic data, testing over 350 growth conditions. iDT1294 achieved a prediction accuracy of 90% for growth with various carbon and nitrogen sources and close to 80% for assimilation of aromatic compounds. Moreover, the M-model accurately predicts dynamic changes of growth and substrate consumption rates over time under nine chemoheterotrophic conditions and demonstrated high precision in predicting metabolic changes between photoheterotrophic and photoautotrophic conditions. This comprehensive M-model will help to elucidate metabolic processes associated with the assimilation of multiple carbon and nitrogen sources, anoxygenic photosynthesis, aromatic compound degradation, as well as production of molecular hydrogen and polyhydroxybutyrate. Author summary: Rhodopseudomonas palustris actively participates in the carbon and nitrogen cycles by fixing carbon dioxide (CO2) and molecular nitrogen (N2), as well as transforming nitrate into N2. This photosynthetic bacterium has been extensively studied and is considered a model microorganism for elucidating carbon and nitrogen fixation, H2 production, denitrification, aromatic compounds degradation, anoxygenic photosynthesis and the production of complex polymers like polyhydroxyalkanoates. Constraint-based metabolic models are systems biology tools capable of predicting an organism's phenotype under several growth conditions. The metabolic model of R. palustris Bis A53, iDT1294, accurately predicts growth rates of over 350 carbon and nitrogen sources (e.g. amino acids, aromatic compounds, organic acids, nucleotides, etc.) under different oxygen and light conditions. Furthermore, iDT1294 precisely simulates how R. palustris switches between photoheterotrophic and photoautotrophic metabolic modes over time, depending on nutrient availability and light conditions. The model represents the most comprehensive M-model for a purple non-sulfur bacterium to date, thus aiding the elucidation of R. palustris' metabolic roles in different environments. [ABSTRACT FROM AUTHOR]

With the development of azo dyes in every aspect of life, azo dyes have brought serious harm to human beings and ecological environment. In this study, a new intimately coupling photocatalysis and biodegradation (ICPB) system was reported: The rod-like graphite carbon nitride-molybdenum disulfide (RCM) of S-scheme was prepared by hydrothermal method and loaded onto the exterior surface of chitosan modified polyurethane sponge (CPU), and Rhodopseudomonas palustris (R. palustris) with metabolic versatility, significant survivability and decomposition to toxic and nonbiodegradable organics was combined inside the carrier. The rod-like RCM and egg-like R. palustris in the CPU were observed, the 13.1° and 27.6° characteristic peaks of g-C 3 N 4 and 33.4° and 57.6° characteristic peaks of MoS 2 were detected, N–H, N C, C–S–Mo, N–Mo bonds were confirmed, and E g = 2.42 eV were calculated in RCM, which confirmed the successful preparation of R. palustris /RCM@CPU. The doping ratio of MoS 2 was 6%, RCM dosage was 0.2 g and chitosan doping ratio was 0.5%, R. palustris /RCM@CPU system showed high degradation efficiency. The removal rates of Congo red, methyl orange and carmine were 99.5%, 97.5% and 99.5%, respectively. The significant removal of R. palustris /RCM@CPU system on azo dyes was due to that the RCM of S-scheme produced strong oxidizing superoxide radical (.O 2 −), hydroxyl radical (.OH) and hole (h+), and could oxidize azo groups and benzene rings of azo dyes to form alkane compounds, which were mineralized by R. palustris. The close cooperation among CPU adsorption, RCM oxidation and R. palustris mineralization effectively enhanced the degradation efficiency of R. palustris /RCM@CPU system for a variety of azo dyes. This study would propose a new means for the degradation efficiency of azo dye wastewater. [Display omitted] • A novel R. palustris /RCM@CPU system was built for rapid degradation of azo dyes. • Performance and mechanism of S-scheme heterojunction RCM photocatalyst were verified. • The system achieved close cooperation and synergy between RCM and R. palustris. • The possible degradation mechanism of R. palustris /RCM@CPU was proposed. [ABSTRACT FROM AUTHOR]

In the present study, an iron(II)-nanoscale organic complex (Fe-NO) was used as an enhancement factor by two different Rhodopseudomonas species of purple non-sulphur bacteria (PNSB) to produce hydrogen (H2). The Fe-NO complex was synthesised using FeSO4·7H2O and Eucalyptus viminalis—a native Australian plant leaf extract—in a 1:2 and 2:1 concentration ratio. Besides, FeSO4·7H2O was also used as a source of iron(II) for comparison with the Fe-NO complex. The photo-fermentative bacterial cultures were isolated from a fishpond, and only two strains, MP3 and SP6, were found viable after several attempts of quadrate streaking. After phylogenetic analysis, these strains were designated as R. palustris MP3 and R. harwoodiae SP6. After comparison with the control, the results showed that the PNSBs manifested an approximately 50% higher H2 yield when the 1:2 Fe-NO complex was used in the fermentation broth at 10 mg/L concentration, where 10.7 ± 0.54 and 10.0 ± 0.49 mL H2/L were obtained by R. palustris MP3 and R. harwoodiae SP6, respectively. The study revealed that the 1:2 Fe-NO complex could be an important material for efficient H2 production. [ABSTRACT FROM AUTHOR]

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The present study embarked on investigating the photo-fermentative bio-H2 production kinetics and statistical optimization of operational parameters using immobilized inoculum from dark fermented palm oil mill effluent (DPOME). The statistical optimized values of initial pH, inoculum-substrate percentage (ISP), and light intensity were achieved by implicating the central composite design (CCD) under response surface methodology (RSM). The kinetic evaluation was conducted in terms of H2-yield with ISP ranged from 10 to 30%. The highest H2 production potential (P) and rate (Rmax) of 30.59 ml.H2/g-CODremoved and 0.514 ml h−1 respectively were achieved with reported lag phase (ρ) value of 32 h by using 20% of ISP. However, an observed Rmax of 0.746 with a ρ value of 39 h was attained at ISP of 15%. The quadratic model developed by using CCD was observed to display the significance value of < 00.5 of probability error. Additionally, observed values of correlation coefficient (R2), adequate precision (AP), and coefficient of variance (CV) for acquired H2-yield were 0.9219, 12.076, and 11.24 ml.H2/g-CODremoved, respectively. Under optimal conditions values (initial pH, 6.0; ISP, 20%; and light intensity, 350% W/m2), H2 yield of 147 ml.H2/g-CODremoved was achieved from DPOME, while reducing the COD value by 78 percentage. This statistical model is suggested to possess the regression, interaction, and quadratic terms as significant, so it can be deemed acceptable in terms of its achievable reproducibility. [ABSTRACT FROM AUTHOR]

Rhodopseudomonas palustris is an alphaproteobacterium with impressive metabolic versatility, capable of oxidizing ferrous iron to fix carbon dioxide using light energy. Photoferrotrophic iron oxidation is one of the most ancient metabolisms, sustained by the pio operon coding for three proteins: PioB and PioA, which form an outer-membrane porin–cytochrome complex that oxidizes iron outside of the cell and transfers the electrons to the periplasmic high potential iron–sulfur protein (HIPIP) PioC, which delivers them to the light-harvesting reaction center (LH-RC). Previous studies have shown that PioA deletion is the most detrimental for iron oxidation, while, the deletion of PioC resulted in only a partial loss. The expression of another periplasmic HiPIP, designated Rpal_4085, is strongly upregulated in photoferrotrophic conditions, making it a strong candidate for a PioC substitute. However, it is unable to reduce the LH-RC. In this work we used NMR spectroscopy to map the interactions between PioC, PioA, and the LH-RC, identifying the key amino acid residues involved. We also observed that PioA directly reduces the LH-RC, and this is the most likely substitute upon PioC deletion. By contrast, Rpal_4085 demontrated significant electronic and structural differences from PioC. These differences likely explain its inability to reduce the LH-RC and highlight its distinct functional role. Overall, this work reveals the functional resilience of the pio operon pathway and further highlights the use of paramagnetic NMR for understanding key biological processes. [ABSTRACT FROM AUTHOR]

The phyllosphere presents a hostile environment for many biocontrol agents; however, it is as significant as is the rhizosphere for plant health. Deploying biocontrol bacteria into the phyllosphere can efficiently suppress diseases; however, the lack of knowledge on the phyllosphere adaptive traits of biocontrol bacteria poses challenges. In this study, we demonstrated that Rhodopseudomonas palustris GJ-22 colonizes the phyllosphere by forming cell aggregates. The formation of cell aggregates required the production of exopolysaccharides (EPS), which depended on the function of the rpaI-rpaR quorum sensing (QS) mechanism, mediated by the signaling molecule p-coumaroyl-HSL (pC-HSL). The mutation of the EPS biosynthesis gene Exop1 or the signaling molecule biosynthesis gene rpaI compromised the ability of GJ-22 to tolerate reactive oxygen intermediates (ROIs), such as H2O2, in vitro and to form cell aggregates in vivo. Collectively, the results revealed that QS mediates EPS production and consequently leads to bacterial cell aggregation. IMPORTANCE Quorum sensing is used by various bacteria for coordinating the multiplication of bacterial cells in a group and for modulating the behaviors of surrounding microbial species. Host plants can benefit from this interspecies modulation, as it can disrupt the QS circuits of pathogenic bacteria. Some N-acyl homoserine lactone- (AHL-) producing bacteria that were introduced into the phyllosphere as biocontrol agents may establish AHL-based crosstalk with indigenous microbes to steer the nutritional and microecological conditions toward their own and the host plant's benefit. Here, we showed that biocontrol bacteria introduced into the phyllosphere require a functioning QS circuit to establish colonies and suppress pathogens. Furthermore, our findings provoked a broader investigation into the role of the QS circuit in beneficial microorganism-plant interactions. [ABSTRACT FROM AUTHOR]