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Enhanced hydrogen evolution was pursued in this work. Rhodobacter sp. (Rb) and Rhodopseudomonas palustris (Rp), single or mixed were used to extract hydrogen molecules from Chlorella fusca biomass. To elevate their fermentable contents, Chlorella was grown at nitrogen and/or phosphorus deprivation. Besides, cellulase and/or macerozyme, Triton X100 or sonicated yeast were applied for further biohydrogen fermentation. Utilizing hydrolysates of mineral deprived Chlorella cultures, Rb exhibited relatively higher cumulative hydrogen (4200 ml L−1) than Rp (2500 ml L−1) while mixed cultures attained significantly higher levels (4700 ml L−1). Triton or enzymes significantly enhanced hydrogen evolution, with more effectiveness of macerozyme than cellulase. A novel use of sonicated yeast, as enzymes pool, induced the highest significant collective H2 (up to 47 times that of microalgal supernatant). Sonicated yeast induced a remarkable hydrolysis of algae, as inferred from increased reducing sugars. However, hydrogen evolution efficiency exhibited poor proportionality with reducing sugars, indicating fermentation of other metabolites.

This study investigated the use of effective microorganisms (EM) to enhance cost-effective biogas purification at household-level application. It involved experimental setups for biogas purification in two different runs: 4 L activated EM and 1 L dormant EM by bubbling biogas through EM purification units. Biogas composition was analyzed using an industry-standard biogas analyzer. The results indicated that EM has the potential for biogas purification through a biological process, to remove H2S and CO2 by involving photosynthetic bacteria (Rhodopseudomonas palustris) in the presence of light. The raw biogas average composition was 62.2% CH4, 37.4% CO2 and 1359.3 ppm H2S. The 4L activated EM batch solution purified the raw biogas to 80.2% CH4, 19.5% CO2 and 786.1 ppm H2S. The corresponding purification efficiencies are 60% for CO2 and 49% for H2S. Purified biogas could be used by the household to cook for 1.82 h (85%) while raw biogas could cover only 55%. The designed biogas purification system can cost only Tshs 91,010/= and purify about 15,000 L of biogas at EM cost of Tshs 9,100/month. Key words: Biogas composition, photosynthetic bacteria, anaerobic digestion, biochemical processes, Rhodopseudomonas palustris, biological desulphurization.

Polyhydroxybutyrate (PHB) is a sustainable bioplastic produced by bacteria that is a potential replacement for conventional plastics. This study delivers an integrated experimental and computational modeling approach to decipher metabolic factors controlling PHB production and offers engineering design strategies to boost production. In the metabolically robust Rhodopseudomonas palustris CGA009, PHB production significantly increased when grown on the carbon- and electron-rich lignin breakdown product p-coumarate (C9H8O3) compared to virtually no PHB titer from acetate (C2H3NaO2). The maximum yield did not improve further when grown on coniferyl alcohol (C10H12O3), but comparison of the PHB profiles showed that coniferyl alcohol's higher carbon content resulted in a higher rate of PHB production. Combined experimental results revealed that cytoplasmic space may be a limiting factor for maximum PHB titer. In order to obtain a systems-level understanding of factors driving PHB yield, a model-driven investigation was performed. The model yielded several engineering design strategies including utilizing reduced, high molecular weight substrates that bypass the thiolase reaction (phaA). Based on these strategies, utilization of butyrate was predicted and subsequently validated to produce PHB. Model analysis also explained why nitrogen starvation was not essential for PHB production and revealed that renewable and abundant lignin aromatics are ideal candidates for PHB production. Most importantly, the generality of the derived design rules allows them to be applied to any PHB-producing microbe with similar metabolic features.

Developing kinetic models to simulate Rhodopseudomonas palustris biohydrogen production within different configurations of photobioreactors (PBRs) poses a significant challenge. In this study, two types of PBRs: schott bottle-based and vertical tubular-based, were investigated, and three original contributions are presented. Firstly, a mechanistic model was constructed to simulate effects of light intensity, light attenuation and temperature on biomass growth and biohydrogen synthesis, previously not unified for photosynthetic bacteria. Secondly, perturbation analysis was exploited to identify critical parameters influencing the accuracy of the model. Thirdly, two parameters: effective light coefficient and biohydrogen enhancement coefficient, both linked to the PBR's transport phenomena were proposed for process scale-up prediction. By comparing against experimental data, the model's accuracy was confirmed to be high. Moreover, the enhancement of biohydrogen production rate by improved culture mixing and gas removal was also described mechanistically. This provides important advances for future efficient design of PBRs and process online optimisation.

Funder: EC | FP7 | Ideas | FP7 Ideas: European Research Council; Grant(s): 854126, The genomes of some purple photosynthetic bacteria contain a multigene puc family encoding a series of α- and β-polypeptides that together form a heterogeneous antenna of light-harvesting 2 (LH2) complexes. To unravel this complexity, we generated four sets of puc deletion mutants in Rhodopseudomonas palustris, each encoding a single type of pucBA gene pair and enabling the purification of complexes designated as PucA-LH2, PucB-LH2, PucD-LH2, and PucE-LH2. The structures of all four purified LH2 complexes were determined by cryogenic electron microscopy (cryo-EM) at resolutions ranging from 2.7 to 3.6 Å. Uniquely, each of these complexes contains a hitherto unknown polypeptide, γ, that forms an extended undulating ribbon that lies in the plane of the membrane and that encloses six of the nine LH2 αβ-subunits. The γ-subunit, which is located near to the cytoplasmic side of the complex, breaks the C9 symmetry of the LH2 complex and binds six extra bacteriochlorophylls (BChls) that enhance the 800-nm absorption of each complex. The structures show that all four complexes have two complete rings of BChls, conferring absorption bands centered at 800 and 850 nm on the PucA-LH2, PucB-LH2, and PucE-LH2 complexes, but, unusually, the PucD-LH2 antenna has only a single strong near-infared (NIR) absorption peak at 803 nm. Comparison of the cryo-EM structures of these LH2 complexes reveals altered patterns of hydrogen bonds between LH2 αβ-side chains and the bacteriochlorin rings, further emphasizing the major role that H bonds play in spectral tuning of bacterial antenna complexes.

The phototrophic bacterium Rhodopseudomonas palustris is emerging as a promising biotechnological chassis organism, due to its resilience to a range of harsh conditions, a wide metabolic repertoire, and the ability to quickly regenerate ATP using light. However, realization of this promise is impeded by a lack of efficient, rapid methods for genetic modification. Here, we present optimized tools for generating chromosomal insertions and deletions employing electroporation as a means of transformation. Generation of markerless strains can be completed in 12 days, approximately half the time for previous conjugation-based methods. This system was used for overexpression of alternative nitrogenase isozymes with the aim of improving biohydrogen productivity. Insertion of the pucBa promoter upstream of vnf and anf nitrogenase operons drove robust overexpression up to 4000-fold higher than wild-type. Transcript quantification was facilitated by an optimized high-quality RNA extraction protocol employing lysis using detergent and heat. Overexpression resulted in increased nitrogenase protein levels, extending to superior hydrogen productivity in bioreactor studies under nongrowing conditions, where promoter-modified strains better utilized the favorable energy state created by reduced competition from cell division. Robust heterologous expression driven by the pucBa promoter is thus attractive for energy-intensive biosyntheses suited to the capabilities of R. palustris. Development of this genetic modification toolset will accelerate the advancement of R. palustris as a biotechnological chassis organism, and insights into the effects of nitrogenase overexpression will guide future efforts in engineering strains for improved hydrogen production.

Coenzyme Q10 (CoQ10 ), a strong antioxidant, is used extensively in food, cosmetic and medicine industries. A natural producer, Rhodopseudomonas palustris (R. palustris), was engineered to overproduce CoQ10 . For increasing the CoQ10 content, crtB gene was deleted to block the carotenoid pathway. crtB gene deletion led to 33% improvement of CoQ10 content over the wild type strain. However, it was found that the yield of hopanoids was also increased by competing for the precursors from carotenoid pathway with CoQ10 pathway. To further increase the CoQ10 content, hopanoid pathway was blocked by deleting shc gene, resulting in R. palustris [Δshc, ΔcrtB] to produce 4.7 mg g-1 DCW CoQ10 , which was 1.2 times higher than the CoQ10 content in the wild type strain. The common strategy of co-expression of rate-limiting enzymes (DXS, DPS and UbiA) was combined with the pathway blocking method resulted in 8.2 mg g-1 DCW of CoQ10 , which was 2.9 times higher than that of wild type strain. The results suggested a synergistic effect among different metabolic engineering strategies. This study demonstrates the potential of R. palustris for CoQ10 production and provides viable strategies to increase CoQ10 titer.

Microbial inoculation is a promising way to improve soil fertility in an eco-friendly manner. Despite the extensive studies of microbial inoculation used for soil biofertilization, their influences on the soil resident microbial community compositions and functions remain poorly understood. Here, we conducted a 130-day pot experiment to test the effects of single and co-inoculation of Rhodopseudomonas palustris and Bacillus subtilis on soil resident bacterial community through sequencing soil microbial 16S ribosomal RNA gene amplicons, as well as the yield and agronomic traits of the rice plant. Microbial inoculations significantly improved the rice yields by 9.84–17.73% (p < 0.05), and R. palustris and B. subtilis inoculant showed synergistic effects on rice yields. The agronomic traits of the rice plants were rarely influenced by the inoculations. We observed that the Shannon diversity of soil resident bacteria remained; however, the community composition changed profoundly with microbial inoculants. The co-inoculation with R. palustris and B. subtilis led to the shift of the relative abundances of plant growth–promoting bacteria in soils, such as Microbacter. The structural equation modeling suggested that soil bacterial community composition greatly contributed to the yield and agronomic traits of the rice plants (r = −0.36 to −0.88, p < 0.05). The soil bacterial community also indirectly mediated the plant growth by affecting microbial enzymatic activities involved in carbon and phosphorus cycling in soils. In general, microbial inoculants directly and indirectly through mediating the soil resident communities enhanced the rice yields.

Rhodopseudomonas palustris is a model microorganism for studying the anaerobic metabolism of aromatic compounds. While it is well documented which aromatics can serve as sole organic carbon sources, co-metabolism of other aromatics is poorly understood. This study used kinetic modeling to analyze the simultaneous degradation of aromatic compounds present in corn stover hydrolysates and model the co-metabolism of aromatics not known to support growth of R. palustris as sole organic substrates. The simulation predicted that p-coumaroyl amide and feruloyl amide were hydrolyzed to p-coumaric acid and ferulic acid, respectively, and further transformed via p-coumaroyl-CoA and feruloyl-CoA. The modeling also suggested that metabolism of p-hydroxyphenyl aromatics was slowed by substrate inhibition, whereas the transformation of guaiacyl aromatics was inhibited by their p-hydroxyphenyl counterparts. It also predicted that substrate channeling may occur during degradation of p-coumaroyl-CoA and feruloyl-CoA, resulting in no detectable accumulation of p-hydroxybenzaldehyde and vanillin, during the transformation of these CoA ligated compounds to p-hydroxybenzoic acid and vanillic acid, respectively. While the simulation correctly represented the known transformation of p-hydroxybenzoic acid via the benzoyl-CoA pathway, it also suggested co-metabolism of vanillic acid and syringic acid, which are known not to serve as photoheterotrophic growth substrate for R. palustris.

G-negative bacteria produce myriad N-acyl-homoserine lactones (AHLs) that can function as quorum sensing (QS) signaling molecules. AHLs are also known to regulate various plant biological activities. p-Coumaroyl-homoserine lactone (pC-HSL) is the only QS molecule produced by a photosynthetic bacterium, Rhodopseudomonas palustris. The role of pC-HSL in the interaction between R. palustris and plant has not been investigated. In this study, we investigated the effect of pC-HSL on plant immunity and found that this QS molecule can induce a systemic resistance to Tobacco mosaic virus (TMV) infection in Nicotiana benthamiana. The results show that pC-HSL treatment can prolong the activation of two mitogen-associated protein kinase genes (i.e., NbSIPK and NbWIPK) and increase the expression of transcription factor WRKY8 as well as immune response marker genes NbPR1 and NbPR10, leading to an increased accumulation of reactive oxygen species (ROS) in the TMV-infected plants. Our results also show that pC-HSL treatment can increase activities of two ROS-scavenging enzymes, peroxidase and superoxide dismutase. Knockdown of NbSIPK or NbWIPK expression in N. benthamiana plants through virus-induced gene silencing nullified or attenuated pC-HSL–induced systemic resistance, indicating that the functioning of pC-HSL relies on the activity of those two kinases. Meanwhile, pC-HSL–pretreated plants also showed a strong induction of kinase activities of NbSIPK and NbWIPK after TMV inoculation. Taken together, our results demonstrate that pC-HSL treatment increases plant resistance to TMV infection, which is helpful to uncover the outcome of interaction between R. palustris and its host plants.

Temperature is a critical parameter for bioprocess performance, requiring careful optimisation for peak efficiency. Green biohydrogen production via photofermentation by purple nonsulfur bacteria including Rhodopseudomonas palustris has been extensively researched, yet realisation is limited by comparatively low productivity. We thus assessed the growth and hydrogen productivity of two closely-related strains of R. palustris acclimated to higher temperatures, revealing markedly increased strain-dependent optima than the 30 °C previously accepted. Strain CGA009 grew 53% faster at 35 °C, with 2.4-fold higher hydrogen production rate, while at 40 °C strain ATH 2.1.37 displayed 86% faster growth and 4-fold higher production rate, along with improved specific production and substrate conversion efficiency. These results reaffirm the necessity of pre-acclimation when verifying temperature optima and expand the feasible temperature range for advancement of high-rate biohydrogen production. Further, the superior heat resistance and production capability of strain ATH 2.1.37 raises the potential for further efficiency gains from thermotolerant environmental isolates.

The production of biohydrogen via photofermentation has been shown to have a low environmental impact and can often be integrated into wastewater treatment systems. However, currently, photofermentation has low production rates in comparison to industrial hydrogen production processes, and therefore requires improvement. One route for enhancing hydrogen productivity is the development of improved photobioreactor (PBR) systems. The aim of this study was to compare the hydrogen productivity of Rhodopseudomonas palustris under planktonic, and immobilized cell conditions, with the reactor operating either as a packed bed or a fluidized bed. The fluidized bed PBR achieved a maximum specific hydrogen production rate and substrate conversion efficiency of 15.74 ± 2.2 mL/g/h and 43% respectively, outperforming the conventional planktonic culture and the packed bed PBR. This work demonstrates a significant improvement in productivity over planktonic photofermentation, as well as demonstrating the use of immobilized cells under reactor conditions not usually associated with photosynthetic systems.

Utilizing solar energy for hydrogen production by combining light-activated materials and biocatalysts has become a promising alternative to fossil fuels. Herein, a feasible and simple bio-hybrid complex based on water-soluble oligofluorene (OF), polythiophene (PTP) and Rhodopseudomonas palustris (R. palustris), one kind of photosynthetic bacteria, was constructed for enhancing photocatalytic hydrogen production. Under the irradiation of visible light, there was fluorescence resonance energy transfer (FRET) between OF and PTP, which amplified photoelectron signals and transferred electrons via PTP to methyl viologen (MV2+), an electron mediator that established electron transfer pathways between organic materials and R. palustris. Hydrogen production involving R. palustris was catalyzed by nitrogenase. It is noteworthy that MV2+ was reduced to MV+˙ and transferred electrons to nitrogenase in R. palustris, converting protons and electrons to molecular hydrogen. Besides, triethanolamine (TEOA) was added as an electron donor to provide electrons to PTP. The proposed OF/PTP/MV2+/TEOA/R. palustris system provided a feasible strategy for photocatalytic hydrogen production with low-cost and easily implemented techniques.

In this study, a portable and disposable paper-based microbial fuel cell (MFC) was fabricated. The MFC was powered by Rhodopseudomonas palustris bacteria (R. palustris). An activated carbon sheet-based anode pre-loaded organic matter (starch) and R. palustris was used. By using starch in the anode, R. palustris-loaded on the anode could be preserved for a long time in dry conditions. The MFC could generate electricity on-demand activated by adding water to the anode. The activated carbon sheet anode was treated by UV-ozone treatment to remove impurities and to improve its hydrophilicity before being loaded with R. palustris. The developed MFC could generate the maximum power density of 0.9 μW/cm2 and could be preserved for long-term usage with little performance degradation (10% after four weeks).

Transforming growth factor β1 (TGFβ1) is a polyfunctional cytokine with important roles in growth, differentiation and immune function in various animals. In this study, PCR, bioinformatics, real-time quantitative PCR, prokaryotic expression, protein purification and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-TOF-MS) were applied to investigate the structural features and function of TGFβ1-b in crucian carp. The complete coding sequence (CDS) of TGFβ1-b was 1134 bp in length and was submitted to GenBank (ID: MH473141). TGFβ1-b encoded a putative protein of 377 amino acids and included a signal peptide consisting of 22 amino acids. TGFβ1-b was relatively conservative in fish and distant from mammals in terms of evolutionary relationship. TGFβ1-b was found to be expressed in various tissues, with the highest expression in the kidney. The expressions of TGFβ1-b in muscle, heart and liver were increased with the addition of Rhodopseudomonas palustris, Bacillus subtilis and Enterococcus faecium at 30 days (p 0.01). While, the expressions of SMAD2, SMAD3 and SMAD7 were also up-regulated with the addition of R. palustris at 20 days (p 0.01). The expression of TGFβ1-b could be affected by time and group factors (p 0.05). Moreover, the expression vector TGFβ1-b-pDE2 was successfully constructed. Prokaryotic expression indicated that a 43 kDa target protein was obtained after induction with 1.5 mM isopropyl-beta-D-thiogalactopyranoside (IPTG) for 3.5 h at 37 °C for 200 r/h. The activities of alkaline phosphatase and lysozyme in injection TGFβ1-b protein group (ITg) and feeding broken bacterial liquid group (BTg) were significantly increased at 24 h (p 0.01). And the activities of superoxide dismutase in ITg were significantly increased at 36 h (p 0.01). Besides, the expressions of heat shock protein 30 and heat shock protein 47 in ITg and BTg were significantly increased (p 0.01). Whereas, the expression of interleukin-11 was significantly reduced (p 0.01). These results indicated that TGFβ1-b protein might play a role in immunity of crucian carp.

A remarkable charge transfer (CT) band is described in the bifurcating electron transfer flavoprotein (Bf-ETF) from Rhodopseudomonas palustris (RpaETF). RpaETF contains two FADs that play contrasting roles in electron bifurcation. The Bf-FAD accepts electrons pairwise from NADH, directs one to a lower-reduction midpoint potential (E°) carrier, and the other to the higher-E° electron transfer FAD (ET-FAD). Previous work noted that a CT band at 726 nm formed when ET-FAD was reduced and Bf-FAD was oxidized, suggesting that both flavins participate. However, existing crystal structures place them too far apart to interact directly. We present biochemical experiments addressing this conundrum and elucidating the nature of this CT species. We observed that RpaETF missing either FAD lacked the 726 nm band. Site-directed mutagenesis near either FAD produced altered yields of the CT species, supporting involvement of both flavins. The residue substitutions did not alter the absorption maximum of the signal, ruling out contributions from residue orbitals. Instead, we propose that the residue identities modulate the population of a protein conformation that brings the ET-flavin and Bf-flavin into direct contact, explaining the 726 nm band based on a CT complex of reduced ET-FAD and oxidized Bf-FAD. This is corroborated by persistence of the 726 nm species during gentle protein denaturation and simple density functional theory calculations of flavin dimers. Although such a CT complex has been demonstrated for free flavins, this is the first observation of such, to our knowledge, in an enzyme. Thus, Bf-ETFs may optimize electron transfer efficiency by enabling direct flavin-flavin contact.

Scanning spectrophotometers equipped with integrating spheres are now readily available commercially. This study explores the possibility of largely escaping from solvent-based determinations of chlorophylls and bacteriochlorophylls using the in vivo absorption spectra to deduce the chlorophyll/bacteriochlorophyll (Chl/BChl) contents of unicellular photosynthetic organisms. Furthermore, we show that scans from ordinary dual beam spectrometers can also be used to estimate the Chl/BChls of unicells in vivo despite light scattering. Spectra of unicellular algae using integrating sphere spectroscopy can measure the absorbance (A) of turbid cell suspensions and hence the in vivo pigment absorption properties of photosynthetic organisms. These results were compared with those obtained using conventional dual beam spectrophotometry scans on turbid cell suspensions and the in solvent spectra of the photosynthetic pigments. The common unicellular green alga, Chlorella sp., is used as an example of an oxygenic photo-organism with Chl a + b, and comparisons were made to other unicellular algae: a cyanobacterium (Synechococcus), a diatom (Chaetoceros) and Acaryochloris. The anoxygenic photosynthetic bacterium Rhodopseudomonas palustris (BChl a) was included in the study. Empirical algorithms are presented for the solvent-free estimation of Chls a, a + b, a + c1c2, d + a and BChl a for the organisms in the study.

Photofermentation seems to be an attractive mode of generating biohydrogen from fermentation effluent. Use of succinate fermentation effluent, however, has not been reported. Rhodobacter sphaeroides KKU-PS1 and Rhodopseudomonas palustris were acclimatised in succinate. It was determined that the KKU-PS1 was superior with respect to hydrogen productivity and was selected for further experiments. Photofermentation in succinate by the KKU-PS1 validated, generating 1217 mL H2/L of cumulative hydrogen at a maximum rate of 6.7 mL H2/L/h. Photofermentation from each single carbon sources that are components of effluent was performed and it was determined that acetate and succinate promoted the fastest growth of KKU-PS1 and hydrogen evolution, respectively. Photofermentation by the strain using mixed substrates mimicking diluted bio-succinate effluent produced yielded 1005 mL H2/L cumulative hydrogen at a maximum rate of 4.1 mL H2/L/h. The study highlighted potential of utilizing bio-succinate fermentation effluent for biohydrogen production, with further optimization required.

Resistance mechanisms of acid Mn2+-resistant purple nonsulfur bacteria (PNSB) were investigated to determine their ability to alleviate adverse effects of excess manganese on plant growth and productivity in acid sulfate soils (ASS). PNSB were isolated and selected based on their resistance to acid and manganese. Their resistance mechanisms were assessed on the basis of biosorption, bioaccumulation, and plant growth promoting properties. Six PNSB were selected for their resistance to Mn2+ in acidic conditions (pH 3.5–5.5). They were identified as Rhodopseudomonas palustris strains TLS12, VNS19, VNS32, VNS62, and VNW95, and Rhodopseudomonas harwoodiae strain TLW42. Under aerobic dark and microaerobic light incubating conditions in aqueous solution at pH 4.25 for 30 min, these strains adsorbed Mn2+ (1500 mg L−1) more effectively with released exopolymeric substances (EPS) than with their biomass. Under both incubating conditions, bioaccumulation of Mn2+ diminished in the following order: cell wall, cytoplasm, plasma membrane. Scanning electron microscope-energy dispersive X-ray spectrometry (SEM-EDS) found accumulated manganese (0.30–0.67% of total elements) in bacterial cells caused morphological change in the form of wrinkles and bleb-like features on exterior surfaces. All selected strains under both incubating conditions released NH4+ by N2 fixing and PO43− by solubilizing phosphate from various P-sources. Siderophores, 5-aminolevulinic acid (ALA), and indole-3-acetic acid (IAA) were also released and pH increased. The studied strains showed potential as bioremediators that could reduce Mn2+ toxicity using EPS and effectively release nutrients and plant growth promoting substances to improve cultivation and fertility in acidic conditions.

Background Removal of dyes from wastewater by microorganisms through adsorption, degradation, or accumulation has been investigated. Biological methods used for dye treatment are generally always effective and environmentally friendly. In this study, biosorption of the Fast Black K salt azo dye by the bacterium Rhodopseudomonas palustris 51ATA was studied spectrophotometrically, at various pH (2–10), temperatures (25°C, 35°C, and 45°C) and dye concentrations (25–400 mg L-1). Results The bacterial strain showed extremely good dye-removing potential at various dye concentrations. IR studies at different temperatures showed that the dye was adsorbed on the bacterial surface at lower temperatures. Characteristics of the adsorption process were investigated by Scatchard analysis at 25°C and 35°C. Scatchard analysis of the equilibrium binding data for the dye on this bacterium gave rise to linear plots, indicating that the Langmuir model could be applied. The regression coefficients obtained for the dye from the Freundlich and Langmuir models were significant and divergence from the Scatchard plot was observed. Conclusion The adsorption behavior of the dye on this bacterium was expressed by the Langmuir, Freundlich, and Temkin isotherms. The adsorption data with respect to various temperatures provided an excellent fit to the Freundlich isotherm. However, when the Langmuir and Temkin isotherm models were applied to these data, a good fit was only obtained for the dye at lower temperatures, thus indicating that the biosorption ability of R. palustris 51ATA is dependent on temperature, pH, and dye concentration. How to cite: Ozturk A, Bayol E, Abdullah MI. Characterization of the biosorption of fast black azo dye K salt by the bacterium Rhodopseudomonas palustris 51ATA strain. Electron J Biotechnol 2020;46. https://doi.org/10.1016/j.ejbt.2020.05.002 .

Late blight caused by the oomycete Phytophthora infestans is the major yield-threatening disease in potato production. An isolate of the photosynthetic bacterium Rhodopseudomonas palustris, GJ-22, was previously evaluated for its ability to promote the growth and enhance the immune response of solanaceous plants. In the present study, GJ-22 was shown to significantly repress disease symptom development caused by P. infestans in potato tubers. Curzate (cymoxanil plus mancozeb), a widely used fungicide with high activity against P. infestans, was selected for use in combination with GJ-22. The sensitivity of GJ-22 to the fungicides cymoxanil and mancozeb was tested. The growth of GJ-22 was unaffected by up to 100 mg l−1 cymoxanil or 50 mg l−1 mancozeb in photosynthetic medium. In greenhouse and field experiments, the combined application of GJ-22 and curzate resulted in better disease control than the use of either agent alone. In addition, treatment with 1 × 107 CFU ml−1 GJ-22 plus 700 mg l−1 curzate showed synergistic effects in the field trial. Our results highlight the potential to control potato late blight with the combination of R. palustris strain GJ-22 and curzate, providing environmentally friendly protection with a reduced level of fungicide application.

All purple photosynthetic bacteria contain RC–LH1 ‘Core’ complexes. The structure of this complex from Rhodobacter sphaeroides, Rhodopseudomonas palustris and Thermochromatium tepidum has been solved using X-ray crystallography. Recently, the application of single particle cryo-EM has revolutionised structural biology and the structure of the RC–LH1 ‘Core’ complex from Blastochloris viridis has been solved using this technique, as well as the complex from the non-purple Chloroflexi species, Roseiflexus castenholzii. It is apparent that these structures are variations on a theme, although with a greater degree of structural diversity within them than previously thought. Furthermore, it has recently been discovered that the only phototrophic representative from the phylum Gemmatimonadetes, Gemmatimonas phototrophica, also contains a RC–LH1 ‘Core’ complex. At present only a low-resolution EM-projection map exists but this shows that the Gemmatimonas phototrophica complex contains a double LH1 ring. This short review compares these different structures and looks at the functional significance of these variations from two main standpoints: energy transfer and quinone exchange.

The genes encoding carbonic anhydrase (CA) were found in all anoxygenic purple bacteria. The genes of α- and β-CA were found in purple nonsulfur bacteria of the class Alphaproteobacteria:Rhodospirillum rubrum, Rhodospirillum fulvum, Rhodoblastus acidophilus, and Rhodopseudomonas palustris. The alphaproteobacteria Rhodomicrobium vannielii, Blastochlorisviridis, Rhodobacter sphaeroides, Rhodobacter capsulatus, Rhodobacter veldkampii, Rhodovulumeuryhalinum, and Rhodovulum sulfidophilum possessed only the β-CA genes. Both nonsulfur purple bacteria of the class Betaproteobacteria (Rubrivivax gelatinosus) and purple sulfur bacteria (class Gammaproteobacteria) contained the α- and β-CA. No CA genes were found in green sulfur bacteria Chlorobaculum limnaeum and Chlorobaculum parvum, as well as in filamentous green nonsulfur bacteria Chloroflexus aurantiacus. However, the β-CA gene was revealed in Oscillochloris trichoides, which belonged to the latter taxonomic group. No γ-CA genes were detected in the genomes of the phototrophic bacteria studied in the present work. Although CA genes were present in all purple bacteria, the α- and β-CA activity was observed only in four species of purple nonsulfur Alphaproteobacteria: Rhodospirillum rubrum, Rhodopseudomonas palustris, Rhodoblastusacidophilus, and Rhodospirillum fulvum. These bacteria are able to synthesize CA under both photoautotrophic and photoheterotrophic conditions in the media with acetate, malate, or fructose. These bacteria (except for Rhodospirillum fulvum, which is unable to grow under aerobic conditions), also exhibit CA activity when grown under aerobic conditions in the dark.

Two-stage process of dark fermentation (DF) and photo fermentation (PF), using fruit and vegetable waste (FVW) and cheese whey powder (CWP), was used as an approach to enhance the hydrogen (H2) production. FVW and CWP at C/N ratios of 34, 39, 60, 71 and 82 were tested as substrates for DF. Dilution (1:2, 1:5, 1:10) of the DF effluents was used as a coupling strategy. DF effluents with low-butyrate and high lactate concentrations were obtained as a function of an increased C/N ratio, which results in high H2 production during the PF. Maximum overall H2 yields of 793.7 and 695.4 mLH2/gChemical Oxygen Demand (COD) were obtained using a 1:10 dilution, at a C/N ratio of 60 and 70, respectively. These H2 yields were higher than those obtained with the individual processes. The C/N ratio at the DF stage regulate not only H2 production but also the distribution and concentrations of by-products. These metabolites, in turn, control the H2 production during the PF. Predominant microbial population for both processes (DF: C/N = 34 Acetobacter lovaniensis, Clostridium butyricum; C/N = 39 C. butyricum, Enterobacter sp, Bifidobacterium; C/N = 82 Lactobacillus casei; PF: Rhodopseudomonas palustris) were in accordance with the final metabolic products.

As a member of photosynthetic bacteria, Rhodopseudomonas palustris, which has extraordinary metabolic versatility, has been applied as one of potential probiotics in feed industry. To explore whether R. palustris can increase rumen microbial viability and thus improve microbial fermentation, a 2×5 factorial experiment was conducted to evaluate the effect of R. palustris at dose rates of 0, 1.3, 2.6, 3.9, 5.2×106 cfu/ml on ruminal fermentation of two representative total mixed rations (HY, a ration for high-yield (>32 kg/d) lactating cows; LY, a ration for low-yield (48) and total volatile fatty acids (VFA, P48 (P2 proportion in headspace of fermentation system was linearly reduced by 46.1% in LY and 32.9% in HY group, respectively (P

This study investigated the regulatory role of Rhodopseudomonas palustris RP11 in alleviating TBBPA-induced harmful effects in soybean seedlings. In this study, the characteristics of growth promotion by strain RP11 were studied by analysing 5-aminolevulinic acid (ALA) and indole-3-acetic acid (IAA) production, as well as phosphorus-solubilizing and potassium-solubilizing ability. In the pot culture conditions, we tested whether strain RP11 improved soybean seedlings tolerance against TBBPA by measuring the root length and physiological parameters of the seedlings treated with strain RP11 and different concentration of TBBPA (0, 5, 50, 100, and 1000 mg/kg) together. The results showed that strain RP11 secreted IAA and ALA, and solubilized phosphate and potassium. In pot trials, strain RP11 increased the root length, chlorophyll content, carotenoid content, soluble sugar and protein content of soybean seedlings treated with TBBPA, in comparison with the seedlings treated only with TBBPA. Furthermore, strain RP11 induced the activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD), decreased the malondialdehyde (MDA) content in soybean seedlings under TBBPA stress. It was concluded that strain RP11 alleviated TBBPA-induced harmful effects in soybean seedlings by the secretion of IAA and ALA, the accumulation of carotenoid, soluble sugar and soluble protein, and the induction of SOD, CAT and POD as well as nutrient adjustment of phosphorus and potassium levels.

By coating photosynthetic bacteria of Rhodopseudomonas palustris with conjugated polymers nanoparticles modified with positively charged peptide TAT (CPNs-TAT), a bio-optical hybrid composite of R....

Harnessing the unique biochemical capabilities of non-model microorganisms would expand the array of biomanufacturing substrates, process conditions, and products. There are non-model microorganisms that fix nitrogen and carbon dioxide, derive energy from light, catabolize methane and lignin-derived aromatics, are tolerant to physiochemical stresses and harsh environmental conditions, store lipids in large quantities, and produce hydrogen. Model microorganisms often only break down simple sugars and require low stress conditions, but they have been engineered for the sustainable manufacture of numerous products, such as fragrances, pharmaceuticals, cosmetics, surfactants, and specialty chemicals, often by using tools from synthetic biology. Transferring complex pathways with all of the needed cofactors, energy sources, and cellular conditions from a non-model microorganism to a common chassis has proven to be exceedingly difficult. Utilization of unique biochemical capabilities could also be achieved by engineering the host; although, synthetic biology tools developed for model microbes often do not perform as designed in other microorganisms. The metabolically versatile Rhodopseudomonas palustris CGA009, a purple non-sulfur bacterium, catabolizes aromatic compounds derived from lignin in both aerobic and anaerobic conditions and can use light, inorganic, and organic compounds for its source of energy. R. palustris utilizes three nitrogenase isozymes to fulfill its nitrogen requirements while also generating hydrogen. Furthermore, the bacterium produces two forms of RuBisCo in response to carbon dioxide/bicarbonate availability. While this potential chassis harbors many beneficial traits, stable heterologous gene expression has been problematic due to its intrinsic resistance to many antibiotics and the lack of synthetic biology parts investigated in this microbe. To address these problems, we have characterized gene expression and plasmid maintenance for different selection markers, started a synthetic biology toolbox specifically for the photosynthetic R. palustris, including origins of replication, fluorescent reporters, terminators, and 5’ untranslated regions, and employed the microbe’s endogenous plasmid for exogenous protein production. This work provides essential synthetic biology tools for engineering R. palustris’ many unique biochemical processes and has helped define the principles for expressing heterologous genes in this promising microbe through a methodology that could be applied to other non-model microorganisms.

Photosynthetic bacteria can be useful biotechnological tools – they produce a variety of valuable products, including high purity hydrogen, and can simultaneously treat recalcitrant wastewaters. However, while photobioreactors have been designed and modelled for photosynthetic algae and cyanobacteria, there has been less work on understanding the effect of light in photosynthetic bacterial fermentations. In order to design photobioreactors, and processes using these organisms, robust models of light penetration, utilisation and conversion are needed. This article uses experimental data from a tubular photobioreactor designed to focus in on light intensity effects, to model the effect of light intensity on the growth of Rhodopseudomonas palustris, a model photosynthetic bacterium. The work demonstrates that growth is controlled by light intensity, and that this organism does experience photoinhibition above 600 W/m2, which has implications for outdoor applications. Further, the work presents a model for light penetration in circular photobioreactors, which tends to be the most common geometry. The work extends the modelling tools for these organisms, and will allow for better photobioreactor design, and the integration of modelling tools in designing processes which use photosynthetic bacteria.

Purple nonsulfur bacteria (PNSB) are metabolically versatile organisms generate energy through both aerobic and anaerobic respiration as well as anoxygenic photosynthesis. In many PNSB, the redox-sensing, two-component system RegBA is a global regulator of energy generating and consuming pathways, such as photosynthesis, carbon fixation, and nitrogen fixation, when cells are shifted from an aerobic to an anaerobic environment. However, in the PNSB Rhodopseudomonas palustris, the role of the RegBA homolog, RegSR, was unclear since global regulation of these same pathways involves the oxygen-sensing signal transduction system, FixJL-K, in R. palustris. Using RNA-seq analysis, we found that RegSR plays a role in regulating the operon pioABC, which encodes genes required for Fe(II) oxidation. We found that transcript levels of pioABC under photoheterotrophic conditions was dependent on the oxidation state of the carbon substrate and whether the cells were fixing nitrogen. We also found that R. palustris can carry out photolithoheterotrophic growth using Fe(II) oxidation when grown with the oxidized carbon substrate, malate, requiring regSR and pioABC. We present a model in which RegSR regulates pioABC in response to a cellular redox signal, allowing R. palustris to use Fe(II) oxidation to access more electrons when there is an increased cellular demand for reducing equivalents.SignificanceMixotrophy is thought to be widespread in aquatic environments, yet little is understood about how mixotrophy affects biogeochemical cycles. Fe(II)-oxidizing anoxygenic phototrophs likely play an important role in iron cycling since they are thought to have thrived in the anoxic, iron-rich oceans of early Earth and can be found in both freshwater and marine environments. Although Fe(II) oxidation by anoxygenic phototrophs is largely studied in the context of photoautotrophic growth, these organisms can also grow photoheterotrophically. We present the first evidence linking photolithoheterotrophic growth using Fe(II) to the pathway required for photoautotrophic Fe(II) oxidation in an anoxygenic phototroph. Understanding this metabolism will be important for understanding how mixotrophic metabolism contributes to iron cycling in anoxic environments.

Background GroEL, which is a chaperone, plays a key role in maintaining protein homeostasis and, among other functions, serves to prevent protein misfolding and aggregation. In addition, the GroEL protein also has a significant effect on enhancing plant resistance and inhibiting plant diseases. However, the function of the GroEL protein in the inhibition of rice blast remains unknown. Result Field experiment results show that photosynthetic bacteria PSB-06 have a good control effect on M. oryzae. PSB-06 also can promote rice growth and enhance the stress resistance. A GroEL protein which was separated and purified from photosynthetic bacteria had a significant antagonistic effect on appressorial formation and pathogenicity of M. oryzae, meanwhile transcriptional analysis demonstrated that the GroEL protein could improve the expression of defense gene of rice. Conclusion Our results show that the photosynthetic bacteria Rhodopseudomonas palustris significantly controls rice blast disease. Its action involves an extracellular GroEL protein, which inhibits appressoria formation, antagonizes the pathogenicity of Magnaporthe oryzae and promotes a host defense response. The research results provide evidence of the potential of this photosynthetic bacterium as biocontrol agent at least for rice blast control. This article is protected by copyright. All rights reserved.

Microbial inoculation is a promising strategy to improve crop yields and reduce the use of chemical fertilizers, thereby creating environment-friendly agriculture. In this study, the long-term (5 years) effects of a phosphate-solubilizing bacterium Burkholderia cepacia ISOP5, a purple non-sulfur bacterium Rhodopseudomonas palustris ISP-1, and a mixed inoculation of these two bacteria (MB) on peanut yield, soil microbial community structure, and microbial metabolic functions were evaluated in a field experiment. After 5 years of inoculation, total peanut yield with B. cepacia ISOP5, R. palustris ISP-1, and MB treatments increased by 8.1%, 12.5%, and 19.5%, respectively. The treatments also significantly promoted the absorption of N and increased the protein content in peanut seeds. Nutrient content also increased to some extent in the bacteria-inoculum-treated soil. However, bacterial community diversity and richness were not significantly affected by bacterial inoculums, and only minor changes occurred in the bacterial community composition. Functional prediction revealed that bacterial inoculums reduced the relative abundance of those genes associated with P uptake and transport as well as increased the abundance of genes associated with inorganic P solubilization and organic P mineralization. Bacterial inoculums also increased the total relative abundance of genes associated with N metabolism. In addition to developing sustainable and eco-friendly agricultural practice, crop inoculation with B. cepacia ISOP5 and R. palustris ISP-1 would improve soil fertility, enhance microbial metabolic activity, and increase crop yield.

Purple nonsulfur bacteria (PNSB) were investigated for their carotenoid production and anti-vibrio activity against acute hepatopancreatic necrosis disease (AHPND)-causing Vibrio parahaemolyticus. To test carotenoid production, selected strains were cultivated in basic isolation medium (BIM), glutamate acetate medium, G5 medium and artificial acetic acid wastewater (AAW) medium. From 144 PNSB, Rhodopseudomonas palustris KTSSG46 was selected to produce carotenoids under microaerobic light conditions in BIM. When the culture medium was optimized, strain KTSSG46 grown in BIM modified with L-glutamate at 1 g/L more effectively inhibited AHPND-causing V. parahaemolyticus strains than standard BIM with 1 g/L (NH4 )2 SO4 . BIM was further modified with 1.23 g/L MgSO4 ·7H2 O and carotenoid production increased 40.22%. Carotenoid production at day 2 by strain KTSSG46 grown in BIM modified with L-glutamate at 1 g/L and 1.23 g/L MgSO4 ·7H2 O was the same as production in BIM modified with monosodium glutamate (MSG). Culture supernatants from all BIM formulations showed similar activity against the resistant AHPND strain SR2. Based on high performance liquid chromatography, carotenoids of strain KTSSG46 might be canthaxanthin. Grown in BIM modified with MSG, strain KTSSG46 could produce inexpensive carotenoids and release anti-vibrio compounds which, applied as shrimp feed additive, would prevent AHPND strains. This article is protected by copyright. All rights reserved.

In natural anoxic environments, anoxygenic photosynthetic bacteria fix CO2 by photoheterotrophy, photoautotrophy, or syntrophic anaerobic photosynthesis. Here, we describe electroautotrophy, a previously unidentified dark CO2 fixation mode enabled by the electrosyntrophic interaction between Geobacter metallireducens and Rhodopseudomonas palustris. After an electrosyntrophic coculture is formed, electrons are transferred either directly or indirectly (via electron shuttles) from G. metallireducens to R. palustris, thereby providing reducing power and energy for the dark CO2 fixation. Transcriptomic analyses demonstrated the high expression of genes encoding for the extracellular electron transfer pathway in G. metallireducens and the Calvin-Benson-Bassham carbon fixation cycle in R. palustris Given that sediments constitute one of the most ubiquitous and abundant niches on Earth and that, at depth, most of the sedimentary niche is both anoxic and dark, dark carbon fixation provides a metabolic window for the survival of anoxygenic phototrophs, as well as an as-yet unappreciated contribution to the global carbon cycle.

Bradyrhizobium diazoefficiens USDA110 is one of the most effective nitrogen-fixing symbionts of soybeans. Here we carried out a large-scale transposon insertion sequencing (Tn-seq) analysis of strain Bd110spc4, which is derived from USDA110, with the goal of increasing available resources for identifying genes crucial for the survival of this plant symbiont under diverse conditions. We prepared two transposon (Tn) insertion libraries of Bd110spc4 with 155,042 unique Tn insertions when the libraries were combined, which is an average of one insertion every 58.7 bp of the reference USDA110 genome. Application of bioinformatic filtering steps to remove genes too small to be expected to have Tn insertions, resulted in a list of genes that were classified as putatively essential. Comparison of this gene set with genes putatively essential for the growth of the closely related alpha-proteobacterium, Rhodopseudomonas palustris, revealed a small set of five genes that may be collectively essential for closely related members of the family Bradyrhizobiaceae. This group includes bacteria with diverse lifestyles ranging from plant symbionts to animal-associated species to free-living species.

High efficient removal of antibiotics during nutriments recovery for biomass production poses a major technical challenge for photosynthetic microbial biofilm-based wastewater treatment since antibiotics are always co-exist with nutriments in wastewater and resist biodegradation due to their strong biotoxicity and recalcitrance. In this study, we make a first attempt to enhance metronidazole (MNZ) removal from wastewater using electrochemistry-activated binary-species photosynthetic biofilm of Rhodopseudomonas Palustris (R. Palustris) and Chlorella vulgaris (C. vulgaris) by cultivating them under different applied potentials. The results showed that application of external potentials of -0.3, 0 and 0.2 V led to 11, 33 and 26-fold acceleration in MNZ removal, respectively, as compared to that of potential free. The extent of enhancement in MNZ removal was positively correlated to the intensities of photosynthetic current produced under different externally applied potentials. The binary-species photoelectrogenic biofilm exhibited 18 and 6-fold higher MNZ removal rate than that of single-species of C. vulgaris and R. Palustris, respectively, due to the enhanced metabolic interaction between them. Application of an external potential of 0V significantly promoted the accumulation of tryptophan and tyrosine-like compounds as well as humic acid in extracellular polymeric substance, whose concentrations were 7.4, 7.1 and 2.0-fold higher than those produced at potential free, contributing to accelerated adsorption and reductive and photosensitive degradation of MNZ.

Purple non-sulfur photosynthetic bacteria such as Rhodobacter sphaeroides and Rhodopseudomonas palustris produce hydrogen gas (H2) via proton reduction, which is catalyzed by nitrogenase. Although the expression of nitrogenase is usually repressed under nitrogen-sufficient conditions, a partial deletion of nifA, which encodes a transcriptional activator of nitrogen-fixation genes, has been reported to enable the constitutive expression of nitrogenase in R. palustris. In this study, we evaluated the effects of a similar mutation (nifA* mutation) on H2 production during the photoheterotrophic growth of R. sphaeroides, based on the notion that H2 production by nitrogenase compensates for the loss of CO2 fixation via the Calvin cycle, thereby restoring the redox balance. The chromosomal nifA* mutation resulted in the slight restoration of the photoheterotrophic growth of a mutant strain lacking ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO), the key enzyme of the Calvin cycle, when the strain was cultured in van Niel's yeast medium. In addition, the strain with the nifA* mutation produced detectable levels of H2 during photoheterotrophic growth with acetate and ammonium; however, the H2 production was considerably lower than that observed during the photoheterotrophic growth of the strain with acetate and L-glutamate, where L-glutamate serves as a poor nitrogen source, thereby causing nitrogenase derepression. On the other hand, introduction of a multicopy plasmid harboring nifA* markedly restored the photoheterotrophic growth of the RubisCO-deletion mutant in van Niel's yeast medium and resulted in efficient H2 production during the photoheterotrophic growth with acetate and ammonium.

We discovered one purple photosynthetic bacterium, Rhodopseudomonas palustris YSC3, which has a specific ability to degrade 1, 2, 5, 6, 9, 10-hexabromocyclododecane (HBCD). The whole transcriptome of R. palustris YSC3 was analyzed using the RNA-based sequencing technology in illumina and was compared as well as discussed through Multi-Omics onLine Analysis System (MOLAS, http://molas.iis.sinica.edu.tw/NTUIOBYSC3/) platform we built. By using genome based mapping approach, we can align the trimmed reads on the genome of R. palustris and estimate the expression profiling for each transcript. A total of 341 differentially expressed genes (DEGs) in HBCD-treated R. palustris (RPH) versus control R. palustris (RPC) was identified by 2-fold changes, among which 305 genes were up-regulated and 36 genes were down-regulated. The regulated genes were mapped to the database of Gene Ontology (GO) and Genes and Genomes Encyclopedia of Kyoto (KEGG), resulting in 78 pathways being identified. Among those DEGs which annotated to important functions in several metabolic pathways, including those involved in two-component system (13.6%), ribosome assembly (10.7%), glyoxylate and dicarboxylate metabolism (5.3%), fatty acid degradation (4.7%), drug metabolism-cytochrome P450 (2.3%), and chlorocyclohexane and chlorobenzene degradation (3.0%) were differentially expressed in RPH and RPC samples. We also identified one transcript annotated as dehalogenase and other genes involved in the HBCD biotransformation in R. palustris. Furthermore, the putative HBCD biotransformation mechanism in R. palustris was proposed.

Massively used plastics have caused worldwide environmental concerns. Polyesters like polylactic acid (PLA) are one of the mostly used plastics due to its excellent physical and chemical properties and low-cost advantages. It is critical to develop the elimination and recycle techniques for polyesters. Experimental studies have shown that a hydrolase RPA1511 isolated from Rhodopseudomonas palustris can efficiently depolymerize polylactic acid (PLA) into oligomers and monomers. It was also active against emulsified aliphatic polymers as well as multipurpose soluble ester monomers (α-naphthyl ester and p-nitrophenyl ester). In the present study, molecular dynamics simulations and molecular mechanics Poisson-Boltzmann surface area method were applied to screen all amino acids from hydrolase RPA1511 and identify the most important amino acids during substrate binding. Seven substrates were considered: PLA (dimer and tetramer), polycaprolactone, butylene succinate, 1-naphthyl acetate, 2-naphthyl formate, p-nitrophenyl acetate. The results highlighted the importance of amino acids like Tyr139, Tyr213, Arg259, Thr46. Subsequent quantum mechanics/molecular mechanics calculations were also performed to determine the detailed degradation mechanism of hydrolase RPA1511 toward PLA and explore the role of the active site residues during catalysis. The results demonstrated that degradation involves two elementary steps: enzyme acylation and PLA hydrolysis. The corresponding Boltzmann average barriers are 20.40 kcal/mol and 14.45 kcal/mol. The electrostatic influence analysis of 15 amino acids on the rate-determining step indicated that amino acids His114, Trp219 and Ala273 facilitate the reaction while the Arg244 suppresses the reaction which may serve as future mutation studies to enhance the enzymatic efficiency.

The enzyme ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) and its central role in capturing atmospheric CO2 via the Calvin-Benson-Bassham (CBB) cycle have been well-studied. Previously, a form II RuBisCO from Rhodopseudomonas palustris, a facultative anaerobic bacterium, was shown to assemble into a hexameric holoenzyme. Unlike previous studies with form II RuBisCO, the R. palustris enzyme could be crystallized in the presence of the transition state analogue 2-carboxyarabinitol 1,5-bisphosphate (CABP), greatly facilitating the structure-function studies reported here. Structural analysis of mutant enzymes with substitutions in form II-specific residues (Ile165 and Met331) and other conserved and semiconserved residues near the enzyme's active site identified subtle structural interactions that may account for functional differences between divergent RuBisCO enzymes. In addition, using a distantly related aerobic bacterial host, further selection of a suppressor mutant enzyme that overcomes negative enzymatic functions was accomplished. Structure-function analyses with negative and suppressor mutant RuBisCOs highlighted the importance of interactions involving different parts of the enzyme's quaternary structure that influenced partial reactions that constitute RuBisCO's carboxylation mechanism. In particular, structural perturbations in an intersubunit interface appear to affect CO2 addition but not the previous step in the enzymatic mechanism, i.e., the enolization of substrate ribulose 1,5-bisphosphate (RuBP). This was further substantiated by the ability of a subset of carboxylation negative mutants to support a previously described sulfur-salvage function, one that appears to rely solely on the enzyme's ability to catalyze the enolization of a substrate analogous to RuBP.

Simultaneous (SPW and cyhalofop-butyl) wastewater treatment and the production of biochemicals by Rhodopseudomonas palustris (R. palustris) was investigated with supplementation of soybean processing wastewater (SPW). Compared to control group, cyhalofop-butyl was removed and single cell protein, carotenoid, bacteriochlorophyll productions were enhanced with the supplementation of SPW. Cyhalofop-butyl removal reached 100% after 5 days under 4000 mg/L COD group. Cyhalofop-butyl induced chbH gene expression to synthesize cyhalofop-butyl-hydrolyzing carboxylesterase through activating MAPKKKs, MAPKKs, MAPKs genes in MAPK signal transduction pathway. The induction process took one day for R. palustris. However, lack of organics in original wastewater did not maintain R. palustris growth for over one day. The supplementation of SPW provided sufficient carbon source. This new method resulted in the mixed wastewater treatment and improvement of biochemicals simultaneously, as well as the realization of reutilization of R. palustris. High-order non-linear mathematical model of the relationship between Rchb, Xc, and Xt was established.

The photosynthetic bacterium, Rhodopseudomonas palustris has been widely used as probiotics in aquaculture, while the molecular basis underlying the probiotic properties of this organism remains largely unknown. In this study, a novel extracellular polysaccharides (RPEPS-30) extracted from the fermentation of Rhodopseudomonas palustris was characterized. Results illustrated that RPEPS-30 was an α-mannan with a molecular weight of 46.82 kDa, which possessed a backbone consisted of 1, 2-linked and 1, 4-linked mannose residues, with side chains composed of 1 → 6 linked and 1 → 2,6 linked mannose residues and substitution at O-6. The in vitro immunomodulatory tests revealed that RPEPS-30 could enhance phagocytic capacity, NO release and mRNA expression of cytokines in macrophages. In addition, RPEPS-30 was shown to promote the growth of resident beneficial gut microbiotasuch as Lactobacillus reuteri, Bacteroides thetaiotaomicron and Akkermansia muciniphila. These findings might help us to partially understand the molecular mechanism concerning the probiotic properties of Rhodopseudomonas palustris, in which the extracellular polysaccharide RPEPS-30 stimulated host immune response and favored the growth of specific benificial micriobiota in the gut.

This study aimed to investigate an inexpensive enrichment medium for obtaining acid-resistant purple nonsulfur bacteria (PNSB) from peat swamp forests (PSF), screening PNSB for their biofertilizer and biocontrol properties, and investigating physico-chemical properties of PSF. Rice straw and G5 broths were used to count PNSB in PSF of Southern Thailand, and isolated PNSB were selected based on the release of nutrients (NH4+ and PO43− from various P-sources), plant growth-promoting substances (PGPS—siderophores, exopolymeric substances, indole-3-acetic acid, and 5-aminolevulinic acid), and inhibiting rice fungal pathogens (Bipolaris oryzae NPT0508 and Curvularia lunata SPB0627). Soil and water samples from primary and secondary PSF of Kan Tulee showed significant differences only for pH in soil and SO42− in water. Almost parameters of both sample types from Kuan Kreng secondary PSF were higher than for Kan Tulee site, except pH. PNSB population was low in both enrichment media and 60 acid-resistant PNSB were isolated. All these were identified as Rhodopseudomonas palustris. R. palustris KKSSR66 was most effective in providing siderophores, NH4+, and PO43−; R. palustris strains KTSWR26, KKSSG39, and KTSWR2 in PGPS production. R. palustris KTSSR54 showed highest inhibition against both rice pathogens. They are potentially beneficial PNSB for rice cultivation in acidic soil.

Fe(II)–organic matter (Fe(II)–OM) complexes are present in the photic zone of aquatic environments and due to their reactivity may play an important role in biogeochemical cycling. Complexation of Fe has been shown to influence the rates and extent of many chemical and microbial redox reactions. However, it is currently unknown whether, how fast, and to which extent Fe(II)–OM complexes can be oxidized by anoxygenic photoautotrophic Fe(II)-oxidizing microorganisms which are widespread in photic habitats and use electrons from Fe(II) to fix CO2. Here, we used the photoautotrophic Fe(II)-oxidizer Rhodopseudomonas palustris TIE-1 to demonstrate that Fe(II) complexation by OM significantly accelerated the rates of Fe(II) oxidation by strain TIE-1 compared to the oxidation of nonorganically bound, free Fe(II), although a fraction of the Fe(II) present as Fe(II)–OM complexes seemed to resist microbial oxidation. Analysis of Fe–OM aggregate sizes showed that the remaining, nonoxidized Fe(II) and almost all of the...

Spontaneous formation of isoaspartates (isoDs) often causes protein damage. l-Isoaspartate O-methyltransferase (PIMT) repairs isoD residues by catalyzing the formation of an unstable l-isoaspartyl methyl ester that spontaneously converts to an l-aspartyl residue. PIMTs are widely distributed in all three domains of life and have been studied most intensively in connection with their role in protein repair and aging in plants and animals. Studies of bacterial PIMTs have been limited to Escherichia coli, which has one PIMT. The α-proteobacterium Rhodopseudomonas palustris has three annotated PIMT genes, one of which (rpa2580) has been found to be important for cellular longevity in a growth-arrested state. However, the biochemical activities of these three R. palustris PIMTs are unknown. Here, we expressed and characterized all three annotated PIMT proteins, finding that two of them, RPA0376 and RPA2838, had PIMT activity, whereas RPA2580 did not. RPA0376 and RPA2838 single- and double-deletion mutants did not differ in longevity from WT R. palustris and did not exhibit elevated levels of isoD residues in aged cells. Comparative sequence analyses revealed that RPA2580 belongs to a separate phylogenetic group of annotated PIMT proteins present in the α-proteobacteria. Our results suggest that this group of proteins is not involved in repair of protein isoD residues. In addition, the bona fide bacterial PIMT enzymes may play a different or subtler role in bacterial physiology than previously suggested.

The simultaneous elimination of organic waste and the production of clean fuels will have an immense impact on both the society and the industrial manufacturing sector. The enhanced understanding of the interface between nanoparticles and photo-responsive bacteria will further advance the knowledge of their interactions with biological systems. Although literature shows the production of gases by photobacteria, herein, we demonstrated the integration of photonics, biology, and nanostructured plasmonic materials for hydrogen production with a lower greenhouse CO2 gas content at quantified light energy intensity and wavelength. Phototrophic purple non-sulfur bacteria were able to generate hydrogen as a byproduct of nitrogen fixation using the energy absorbed from visible and near-IR (NIR) light. This type of biological hydrogen production has suffered from low efficiency of converting light energy into hydrogen in part due to light sources that do not exploit the organisms' capacity for NIR absorption. We used NIR light sources and optically resonant gold–silica core–shell nanoparticles to increase the light utilization of the bacteria to convert waste organic acids such as acetic and maleic acids to hydrogen. The batch growth studies for the small cultures (40 mL) of Rhodopseudomonas palustris demonstrated >2.5-fold increase in hydrogen production when grown under an NIR source (167 ± 18 μmol H2) compared to that for a broad-band light source (60 ± 6 μmol H2) at equal light intensity (130 W m−2). The addition of the mPEG-coated optically resonant gold–silica core–shell nanoparticles in the solution further improved the hydrogen production from 167 ± 18 to 398 ± 108 μmol H2 at 130 W m−2. The average hydrogen production rate with the nanoparticles was 127 ± 35 μmol L−1 h−1 at 130 W m−2.