Formation of NifA-PII complex represses ammonium-sensitive nitrogen fixation in diazotrophic proteobacteria lacking NifL.

Biological nitrogen fixation catalyzed by nitrogenase contributes greatly to the global nitrogen cycle. Nitrogenase expression is subject to regulation in response to nitrogen availability. However, the mechanism through which the transcriptional activator NifA regulates nitrogenase expression by interacting with PII nitrogen regulatory proteins remains unclear in diazotrophic proteobacteria lacking NifL. Here, we demonstrate that in Rhodopseudomonas palustris grown with ammonium, NifA bound deuridylylated PII proteins to form an inactive NifA-PII complex, thereby inhibiting the expression of nitrogenase. Upon nitrogen limitation, the dissociation of uridylylated PII proteins from NifA resulted in the full restoration of NifA activity, and, simultaneously, uridylylation of the significantly up-regulated PII protein GlnK2 led to the increased expression of NifA in R. palustris. This insight into how NifA interacts with PII proteins and controls nitrogenase expression sets the stage for creating highly efficient diazotrophs, reducing the need for energy-intensive chemical fertilizers and helping to diminish carbon emissions.

Recent advancements in wastewater treatment via anaerobic fermentation process: A systematic review.

This manuscript delves into the realm of wastewater treatment, with a particular emphasis on anaerobic fermentation processes, especially dark, photo, and dark-photo fermentation processes, which have not been covered and overviewed previously in the literature regarding the treatment of wastewater. Moreover, the study conducts a bibliometric analysis for the first time to elucidate the research landscape of anaerobic fermentation utilization in wastewater purification. Furthermore, microorganisms, ranging from microalgae to bacteria and fungi, emphasizing the integration of these agents for enhanced efficiency, are all discussed and compared. Various bioreactors, such as dark and photo fermentation bioreactors, including tubular photo bioreactors, are scrutinized for their design and operational intricacies. The results illustrated that using clostridium pasteurianum CH4 and Rhodopseudomonas palustris WP3-5 in a combined dark-photo fermentation process can treat wastewater to a pH of nearly 7 with over 90% COD removal. Also, integrating Chlorella sp and Activated sludge can potentially treat synthetic wastewater to COD, P, and N percentage removal rates of 99%,86%, and 79%, respectively. Finally, the paper extends to discuss the limitations and future prospects of dark-photo fermentation processes, offering insights into the road ahead for researchers and scientists.

Growth of electroautotrophic microorganisms using hydrovoltaic energy through natural water evaporation.

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.

Light harvesting in purple bacteria does not rely on resonance fine-tuning in peripheral antenna complexes.

The ring-like peripheral light-harvesting complex 2 (LH2) expressed by many phototrophic purple bacteria is a popular model system in biological light-harvesting research due to its robustness, small size, and known crystal structure. Furthermore, the availability of structural variants with distinct electronic structures and optical properties has made this group of light harvesters an attractive testing ground for studies of structure-function relationships in biological systems. LH2 is one of several pigment-protein complexes for which a link between functionality and effects such as excitonic coherence and vibronic coupling has been proposed. While a direct connection has not yet been demonstrated, many such interactions are highly sensitive to resonance conditions, and a dependence of intra-complex dynamics on detailed electronic structure might be expected. To gauge the sensitivity of energy-level structure and relaxation dynamics to naturally occurring structural changes, we compare the photo-induced dynamics in two structurally distinct LH2 variants. Using polarization-controlled 2D electronic spectroscopy at cryogenic temperatures, we directly access information on dynamic and static disorder in the complexes. The simultaneous optimal spectral and temporal resolution of these experiments further allows us to characterize the ultrafast energy relaxation, including exciton transport within the complexes. Despite the variations in PPC molecular structure manifesting as clear differences in electronic structure and disorder, the energy-transport and-relaxation dynamics remain remarkably similar. This indicates that the light-harvesting functionality of purple bacteria within a single LH2 complex is highly robust to structural perturbations and likely does not rely on finely tuned electronic- or electron-vibrational resonance conditions.

Unnatural Direct Interspecies Electron Transfer Enabled by Living Cell-Cell Click Chemistry.

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.

Deciphering the differentiated performance on electricity generation and COD degradation by Rhodopseudomonas-dominated bioanode in light or dark.

Anoxygenic phototrophic bacteria is a promising catalyst for constructing bioanode, but the mixed culture with non-photosynthetic bacteria is inevitable in an open environment application. In this study, a Rhodopseudomonas-dominated mixed culture with other electrogenic bacteria was investigated for deciphering the differentiated performance on electricity generation in light or dark conditions. The kinetic study showed that reaction rate of OM degradation was 9 times higher than that under dark condition, demonstrating that OM degradation was enhanced by photosynthesis. However, CE under light condition was lower. It indicated that part of OM was used to provide hydrogen donors for the fixation of CO2 or hydrogen production in photosynthesis, decreasing the OM used for electron transfer. In addition, higher COD concentration was not conducive to electricity generation. EIS analysis demonstrated that higher OM concentration would increase Rct to hinder the transfer of electrons from bacteria to the electrode. Indirect and direct electron transfer were revealed by CV analysis for light and dark biofilm, respectively, and nanowires were also observed by SEM graphs, further revealing the differentiate performance. Microbial community analysis demonstrated Rhodopseudomonas was dominated in light and decreased in dark, but Geobacter increased apparently from light to dark, resulting in different power generation performance. The findings revealed the differentiated performance on electricity generation and pollutant removal by mixed culture of phototrophic bacteria in light or dark, which will improve the power generation from photo-microbial fuel cells.

Development of an electrochemical separation-Rhodopseudomonas palustris electrolysis cell-coupled system for resourceful treatment of mature leachate landfill.

Electrochemical technology is a promising technique for separating ammonia from mature landfill leachate. However, the accompanying migration and transformation of coexisting pollutants and strategies for further high-value resourceful utilization of ammonia have rarely received attention. In this study, an electrochemical separation-Rhodopseudomonas palustris electrolysis cell coupled system was initially constructed for efficient separation and conversion of nitrogen in mature landfill leachate to microbial protein with synchronously tracking the transport and conversion of coexisting heavy metals accompanying the process. The results revealed that ammonia concentration in the cathode increased from 40.3 to 49.8% with increasing the current density from 20 to 40 mA/cm2, with less than 3% of ammonia transformation to NO2--N and NO3--N. During ammonia separation, approximately 95% of HM-DOMs (Cr, Cu, Ni, Pb, and Zn) were released into the anolyte due to humus degradation and further diffused to the cathode. A significant correlation was observed between the releases of HM-DOMs. Cu-DOMs accounted for 70.2% of the total Cu content, which was the highest proportion among the heavy metals (HMs). Among the HMs in anolyte, 57.4% of Pb, 52.5% of Ni, and 50.6% of Zn diffused to the cathode, and most of the HMs were removed in the form of hydroxide precipitations due to heavy alkaline catholyte. Compared with the open-circuit condition, the utilization efficiency of NH4+-N in the R. palustris electrolysis cell increased by 445.1% with 47% and 50% increases in final NH4+-N conversion rate and R. palustris biomass, respectively, due to bio-electrochemical enhanced phototrophic metabolism and acid generation for buffering the strong alkalinity of the electrolyte to maintain suitable growth conditions for R. palustris.

Rhodopseudomonas palustris shapes bacterial community, reduces Cd bioavailability in Cd contaminated flooding paddy soil, and improves rice performance.

Photosynthetic bacteria (PSB) are suitable to live and remediate cadmium (Cd) in the slightly oxygenated or anaerobic flooding paddy field. However, there is currently limited study on the inhibition of Cd accumulation in rice by PSB, and the relevant mechanisms has yet to be elucidated. In the current study, we firstly used Rhodopseudomonas palustris SC06 (a typical PSB) as research target and combined physiology, biochemistry, microbiome and metabolome to evaluate the mechanisms of remeding Cd pollution in paddy field and inhibiting Cd accumulation in rice. Microbiome analysis results revealed that intensive inoculation with R. palustris SC06 successfully survived and multiplied in flooding paddy soil, and significantly increased the relatively abundance of anaerobic bacteria including Desulfobacterota, Anaerolineaceae, Geobacteraceae, and Gemmatimonadaceae by 46.40 %, 45.00 %, 50.12 %, and 21.30 %, respectively. Simultaneously, the structure of microbial community was regulated to maintain relative stability in the rhizosphere soil of rice under Cd stress. In turn, these bacteria communities reduced bioavailable Cd and enhanced residual Cd in soil, and induced the upregulation of sugar and organic acids in the rice roots, which further inhibited Cd uptake in rice seedlings, and dramatically improved the photosynthetic efficiency in the leaves and the activities of antioxidative enzymes in the roots. Finally, Cd content of the roots, stems, leaves, and grains significantly decreased by 38.14 %, 69.10 %, 83.40 %, and 37.24 % comparing with the control, respectively. This study provides a new strategy for the remediation of Cd-contaminated flooding paddy fields and the safe production of rice.

Outdoor biohydrogen production by thermotolerant Rhodopseudomonas pentothenatexigens KKU-SN1/1 in a cluster of ten bioreactors system.

In tropical regions, the viability of outdoor photo-fermentative biohydrogen production faces challenges arising from elevated temperatures and varying light intensity. This research aimed to explore how high temperatures and outdoor environments impact both biohydrogen production and the growth of purple non-sulfur bacteria. Our findings revealed the potential of Rhodopseudomonas spp. as a robust outdoor hydrogen-producing bacteria, demonstrating its capacity to thrive and generate biohydrogen even at 40 °C and under fluctuating outdoor conditions. Rhodopseudomonas harwoodiae NM3/1-2 produced the highest cumulative biohydrogen of 223 mL/L under anaerobic light conditions at 40 °C, while Rhodopseudomonas harwoodiae 2M had the highest dry cell weight of 2.93 g/L. However, R. harwoodiae NM3/1-2 demonstrated the highest dry cell weight of 3.99 g/L and Rhodopseudomonas pentothenatexigens KKU-SN1/1 exhibited the highest cumulative biohydrogen production of 400 mL/L when grown outdoors. In addition, the outdoor enhancement of biohydrogen production was achieved through the utilization of a cluster of ten bioreactors system. The outcomes demonstrated a notable improvement in biohydrogen production efficiency, marked by the highest daily biohydrogen production of 493 mL/L d by R. pentothenatexigens KKU-SN1/1. Significantly, the highest biohydrogen production rate was noted to be 17 times greater than that observed in conventional batch production methods. This study is the first to utilize R. pentothenatexigens and R. harwoodiae for sustained biohydrogen production at high temperatures and in outdoor conditions over an extended operational period. The successful utilization of a clustered system of ten bioreactors demonstrates potential to scale-up for industrial biohydrogen production.

Phototrophic Fe(II) oxidation by Rhodopseudomonas palustris TIE-1 in organic and Fe(II)-rich conditions.

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). 57 Fe 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.

Effect of the addition of an inorganic carbon source on the degradation of sotol vinasse by Rhodopseudomonastelluris.

The difficulty of the microbial conversion process for the degradation of sotol vinasse due to its high acidity and organic load makes it an effluent with high potential for environmental contamination, therefore its treatment is of special interest. Calcium carbonate is found in great abundance and has the ability to act as a neutralizing agent, maintaining the alkalinity of the fermentation medium as well as, through its dissociation, releasing CO2 molecules that can be used by phototrophic CO2-fixing bacteria. This study evaluated the use of Rhodopseudomonas telluris (OR069658) for the degradation of vinasse in different concentrations of calcium carbonate (0, 2, 4, 6, 8 and 10% m/v). The results showed that calcium carbonate concentration influenced volatile fatty acids (VFA), alkalinity and pH, which in turn influenced changes in the degradation of chemical oxygen demand (COD), phenol and sulfate. Maximum COD and phenol degradation values of 83.16 ± 0.15% and 90.16 ± 0.30%, respectively, were obtained at a calcium carbonate concentration of 4%. At the same time, the lowest COD and phenol degradation values of 52.01 ± 0.38% and 68.21 ± 0.81%, respectively, were obtained at a calcium carbonate concentration of 0%. The data obtained also revealed to us that at high calcium carbonate concentrations of 6-10%, sotol vinasse can be biosynthesized by Rhodopseudomonas telluris (OR069658) to VFA, facilitating the degradation of sulfates. The findings of this study confirmed the potential for using Rhodopseudomonas telluris (OR069658) at a calcium carbonate concentration of 4% as an appropriate alternative treatment for sotol vinasse degradation.

Evolution of Rhodopseudomonas palustris to degrade halogenated aromatic compounds involves changes in pathway regulation and enzyme specificity.

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.IMPORTANCEBiodegradation of man-made compounds often involves the activity of promiscuous enzymes whose native substrate is structurally similar to the man-made compound. Based on the enzymes involved, it is possible to predict what microorganisms are likely involved in biodegradation of anthropogenic compounds. However, there are examples of organisms that contain the required enzyme(s) and yet cannot metabolize these compounds. We found that even when the purple nonsulfur bacterium, Rhodopseudomonas palustris, encodes all the enzymes required for degradation of a halogenated aromatic compound, it is unable to metabolize that compound. Using adaptive evolution, we found that a regulatory mutation and a variant of promiscuous enzyme with increased substrate specificity were required. This work provides insight into how an environmental isolate evolved to use a halogenated aromatic compound.

The potency of a liquid biofertilizer containing bacterial strains of Rhodopseudomonas spp. on recovery of soil properties damaged by Al3+ and Fe2+ toxins and enhancement of rice yield in acid sulfate soil.

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.

Synergistic molecular mechanism of degradation in dye wastewater by Rhodopseudomonas palustris intimately coupled carbon nanotube - Silver modified titanium dioxide photocatalytic composite with sodium alginate.

The intimately coupled photocatalysis and biodegradation (ICPB), which combined the advantages of high oxidation capacity of photocatalysis and high mineralization rate of biodegradation, has demonstrated excellent removal performance in the degradation of azo dyes with highly toxic, refractory, mutagenic and carcinogenic. In order to explore the metagenomics mechanism of the ICPB system, a novel ICPB was prepared by coupling Rhodopseudomonas palustris (R. Palustris), carbon nanotube - silver modified titanium dioxide photocatalytic composite (CNT-Ag -TiO2, CAT) and sodium alginate (SA) (R. palustris/CAT@SA, R-CAT). Metagenomics sequencing was used to investigate the molecular mechanism of adaptation and degradation of dyes by photosynthetic microorganisms and the adaptive and synergistic interaction between photosynthetic microorganisms and photocatalyst. Experiments on the adaptability and degradability of photosynthetic microorganisms have proved that low concentration azo dyes could be utilized as carbon sources for growth of photosynthetic microorganisms. Metagenomics sequencing revealed that R. palustris was the main degrading bacterium in photosynthetic microorganisms and the functional genes related to carbohydrate metabolism, biological regulation and catalytic activity were abundant. It was found that the addition of photocatalyst significantly up-regulated the functional genes related to the catabolic process, electron transport, oxidoreductase activity and superoxide metabolism of organic matter in the photosynthetic microorganisms. Moreover, many key gene such as alpha-amylase, 1-acyl-sn-glycerol-3-phosphate acyltransferase, aldehyde dehydrogenase enrichment in microbial basal metabolism, such as enoyl-CoA hydratase, malate dehydrogenase, glutathione S-transferase enrichment in degrading azo dyes and electron transport, and many key gene such as undecaprenyl-diphosphatase, carbon storage regulator, DNA ligase enrichment in response to dyes and photocatalysts were discovered. These findings would contribute to a comprehensive understanding of the mechanism of degradation of dye wastewater by ICPB system, a series of genes was produced to adapt to environmental changes, and played synergistic role in terms of intermediate product degradation and electron transfer for degrading azo dyes. The photosynthetic microorganisms might be a promising microorganism for constructing ICPB system.

Characterization of the Pyrroloquinoline Quinone Producing Rhodopseudomonas palustris as a Plant Growth-Promoting Bacterium under Photoautotrophic and Photoheterotrophic Culture Conditions.

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. palustris's 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 PNSB's growing conditions, it may interact with various soil bacteria and facilitate their infiltration into plants.

Removal of pollutants and accumulation of high-value cell inclusions in a batch reactor containing Rhodopseudomonas for treating real heavy oil refinery wastewater.

Treating wastewater using purple non-sulfur bacteria (PNSB) is an environmentally friendly technique that can simultaneously remove pollutants and lead to the accumulation of high-value cell inclusions. However, no PNSB system for treating heavy oil refinery wastewater (HORW) and recovering high-value cell inclusions has yet been developed. In this study, five batch PNSB systems dominated by Rhodopseudomonas were used to treat real HORW for 186 d. The effects of using different hydraulic retention times (HRT), sludge retention times (SRT), trace element solutions, phosphate loads, and influent loads were investigated, and the bacteriochlorophyll, carotenoid, and coenzyme Q10 concentrations were determined. The community structure and quantity of Rhodopseudomonas in the systems were determined using a high-sequencing technique and quantitative polymerase chain reaction technique. The long-term results indicated that phosphate was the limiting factor for treating HORW in the PNSB reactor. The soluble chemical oxygen demand (SCOD) removal rates were 67.03% and 85.26% without and with phosphate added, respectively, and the NH4+-N removal rates were 32.18% and 89.22%, respectively. The NO3--N concentration in the effluent was stable at 0-3 mg/L with or without phosphate added. Adding phosphate increased the Rhodopseudomonas relative abundance and number by 13.21% and 41.61%, respectively, to 57.35% and 8.52 × 106 gene copies/µL, respectively. The SRT was the limiting factor for SCOD removal, and the bacteria concentration was the limiting factor for nitrogen removal. Once the inflow load had been increased, the total nitrogen (TN) removal rate increased as the HRT increased. Maximum TN removal rates of 64.46%, 68.06%, 73.89%, 82.15%, and 89.73% were found at HRT of 7, 10, 13, 16, and 19 d, respectively. The highest bacteriochlorophyll, carotenoid, and coenzyme Q10 concentrations were 2.92, 4.99, and 4.53 mg/L, respectively. This study provided a simple and efficient method for treating HORW and reutilizing resources, providing theoretical support and parameter guidance for the application of Rhodopseudomonas in treating HORW.

The genome-scale metabolic model for the purple non-sulfur bacterium Rhodopseudomonas palustris Bis A53 accurately predicts phenotypes under chemoheterotrophic, chemoautotrophic, photoheterotrophic, and photoautotrophic growth conditions.

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.

Stability and biomineralization of cadmium sulfide nanoparticles biosynthesized by the bacterium Rhodopseudomonas palustris under light.

Cadmium (Cd) pollution is regarded as a potent problem due to its hazard risks to the environment, making it crucial to be removed. Compared to the physicochemical techniques (e.g., adsorption, ion exchange, etc.), bioremediation is a promising alternative technology for Cd removal, due to its cost-effectiveness, and eco-friendliness. Among them, microbial-induced cadmium sulfide mineralization (Bio-CdS NPs) is a process of great significance for environmental protection. In this study, microbial cysteine desulfhydrase coupled with cysteine acted as a strategy for Bio-CdS NPs by Rhodopseudomonas palustris. The synthesis, activity, and stability of Bio-CdS NPs-R. palustris hybrid was explored under different light conditions. Results show that low light (LL) intensity could promote cysteine desulfhydrase activities to accelerate hybrid synthesis, and facilitated bacterial growth by the photo-induced electrons of Bio-CdS NPs. Additionally, the enhanced cysteine desulfhydrase activity effectively alleviated high Cd-stress. However, the hybrid rapidly dissolved under changed environmental factors, including light intensity and oxygen. The factors affecting the dissolution were ranked as follows: darkness/microaerobic ≈ darkness/aerobic < LL/microaerobic < high light (HL)/microaerobic < LL/aerobic < HL/aerobic. The research provides a deeper understanding of Bio-CdS NPs-bacteria hybird synthesis and its stability in Cd-polluted water, allowing advanced bioremediation treatment of heavy metal pollution in water.

Protein Interactions in Rhodopseudomonas palustris TIE-1 Reveal the Molecular Basis for Resilient Photoferrotrophic Iron Oxidation.

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.