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Roseiflexus castenholzii is an ancient green non-sulfur bacteria that absorbs the solar energy through bacteriochlorophylls (BChls) bound in the only light harvesting (LH) complex, and transfers to the reaction center (RC), wherein primary charge separation occurs and transforms the energy into electrochemical potentials. In contrast to purple bacteria, R. castenholzii RC-LH (rc RC-LH) does not contain an H subunit. Instead, a tightly bound tetraheme cytochrome c subunit is exposed on the P-side of the RC, which contains three BChls, three bacteriopheophytins (BPheos), two menaquinones, and one iron for electron transfer. These novel structural features of the rc RC-LH are advantageous for enhancing the electron transfer efficiency and subsequent photo-oxidation of the c -type hemes. However, the photochemical properties of rc RC-LH and its applications in developing the photo-bioelectrochemical cells (PBECs) have not been characterized. Here, we prepared a PBEC using overlapped fluorine-doped tin oxide (FTO) glass and Pt-coated glass as electrodes, and rc RC-LH mixed with varying mediators as the electrolyte. Absence of the H subunit allows rc RC-LH to be selectively adhered onto the hydrophilic surface of the front electrode with its Q-side. Upon illumination, the photogenerated electrons directly enter the front electrode and transfer to the counter electrode, wherein the accepted electrons pass through the exposed c -type hemes to reduce the excited P+, generating a steady-state current of up to 320 nA/cm2 when using 1-Methoxy-5-methylphenazinium methyl sulfate (PMS) as mediator. This study demonstrated the novel photoelectric properties of rc RC-LH and its advantages in preparing effective PBECs, showcasing a potential of this complex in developing new type PBECs. [ABSTRACT FROM AUTHOR]

The mildly thermophilic purple phototrophic bacterium Allochromatium tepidum provides a unique model for investigating various intermediate phenotypes observed between those of thermophilic and mesophilic counterparts. The core light-harvesting (LH1) complex from A. tepidum exhibits an absorption maximum at 890 nm and mildly enhanced thermostability, both of which are Ca2+-dependent. However, it is unknown what structural determinants might contribute to these properties. Here, we present a cryo-EM structure of the reaction center–associated LH1 complex at 2.81 Å resolution, in which we identify multiple pigment-binding α- and β-polypeptides within an LH1 ring. Of the 16 α-polypeptides, we show that six (α1) bind Ca2+ along with β1- or β3-polypeptides to form the Ca2+-binding sites. This structure differs from that of fully Ca2+-bound LH1 from Thermochromatium tepidum, enabling determination of the minimum structural requirements for Ca2+-binding. We also identified three amino acids (Trp44, Asp47, and Ile49) in the C-terminal region of the A. tepidum α1-polypeptide that ligate each Ca ion, forming a Ca2+-binding WxxDxI motif that is conserved in all Ca2+- bound LH1 α-polypeptides from other species with reported structures. The partial Ca2+-bound structure further explains the unusual phenotypic properties observed for this bacterium in terms of its Ca2+-requirements for thermostability, spectroscopy, and phototrophic growth, and supports the hypothesis that A. tepidum may represent a “transitional” species between mesophilic and thermophilic purple sulfur bacteria. The characteristic arrangement of multiple αβ-polypeptides also suggests a mechanism of molecular recognition in the expression and/or assembly of the LH1 complex that could be regulated through interactions with reaction center subunits. [ABSTRACT FROM AUTHOR]

Rhodovulum spp. are anoxygenic phototrophic purple bacteria with versatile metabolisms, including the ability to obtain electrons from minerals in their environment to drive photosynthesis, a relatively novel process called phototrophic extracellular electron uptake (pEEU). A total of 15 strains of Rhodovulum sulfidophilum were isolated from a marine estuary to observe these metabolisms in marine phototrophs. One representative strain, Rhodovulum sulfidophilum strain AB26, can perform phototrophic iron oxidation (photoferrotrophy) and couples carbon dioxide fixation to pEEU. Here, we reclassify two R. sulfidophilum isolates, strainAB26 and strain AB19, as Rhodovulum visakhapatnamense using taxonomic re-evaluation based on 16S and pufM phylogenetic analyses. The strain AB26 genome consists of 4,380,746 base-pairs, including two plasmids, and encodes 4296 predicted protein-coding genes. Strain AB26 contains 22 histidine kinases, 20 response regulators, and dedicates ~16% of its genome to transport. Transcriptomic data under aerobic, photoheterotrophy, photoautotrophy, and pEEU reveals how gene expression varies between metabolisms in a novel R. visakhapatnamense strain. Genome comparison led by transcriptomic data under pEEU reveals potential pEEU-relevant genes both unique to R. visakhapatnamense strains and shared within the R. sulfidophilum genomes. With these data we identify potential pEEU-important transcripts and how speciation may affect molecular mechanisms of pEEU in Rhodovulum species from the same environment. [ABSTRACT FROM AUTHOR]

[Display omitted] • ZnO/ZnS boosts cumulative hydrogen yield by 30% in photo-fermentation. • Nanomaterials enhanced bacterial extracellular polymer accumulation. • The mechanism of ZnO/ZnS in photo-fermentation hydrogen production was discussed. This study incorporated ZnO/ZnS nanoparticles with Rhodobacter capsulatus SB1003, forming a hybrid system to promote photo-fermentative hydrogen production. The results indicate that the material's photocatalytic activity and concentration significantly affected hydrogen yield. The addition of ZnO/ZnS exhibited a more significant auxiliary effect than ZnO and achieved an approximately 30% increase in hydrogen production compared to the control group. ZnO/ZnS enhanced the production of extracellular polymers, thereby strengthening the synergy between the nanomaterials and the bacteria. The photogenerated electrons from ZnO/ZnS were utilized by the photosynthetic bacteria. Furthermore, the activity of nitrogenase was enhanced, resulting in improved hydrogen production performance. This study provides insights into hydrogen production by photosynthetic bacteria with the assistance of inorganic semiconductor nanomaterials. [ABSTRACT FROM AUTHOR]

The ability to generate polyphosphate (polyP) granules is important for survival for bacteria during resistance to diverse environmental stresses, however the genesis of polyP granules is poorly understood. Chlorobaculum tepidum (Cba tepidum) is a thermophilic green sulfur anoxygenic phototrophic bacterium which uses reduced sulfur compounds as electron donors. The presence of electron rich granules inside the Cba tepidum was reported, but no further information was provided. In this work we used cell thin sections at three different time points of cultivation to observe the biogenesis of the inclusions over time, and the in cell total phosphate concentration was monitored over time as well. Furthermore, the elemental analysis (EDS) of the electron rich inclusions showed the presence of phosphorus and oxygen. The existence of polyphosphate was demonstrated by 31P NMR spectroscopy of cell lysates. Finally, we show that the biogenesis of the phosphorus granules correlates with an abundance of proteins that are closely related to polyphosphate metabolism. • Existence of polyphosphate granules in Chlorobaculum tepidum an ancestral photoautotrophic bacterium. • The biogenesis of polyphosphate granules in the cells of Chlorobaculum tepidum was monitored over time by TEM. • Elemental analysis (EDS) of the granules showed the presence of phosphorus and oxygen. • The existence of polyphosphate was demonstrated by 31P NMR spectroscopy of cell lysates. • The biogenesis of the phosphorus granules correlates with an abundance of proteins related to polyphosphate metabolism. [ABSTRACT FROM AUTHOR]

[Display omitted] • Purple non-sulfur bacteria (PNSB) enriched from anaerobic sludge under infrared light. • Photoheterotrophic growth and recovery of PNSB was performed using fermented sewage. • Impact of area/volume ratio on treated wastewater quality and biomass yield evaluated. • The biomass of 0.9 g VSS/L with protein contents of 43.9 ± 0.2 % w/w was obtained. • Raceway pond having PNSB removed COD (89.0 %), NH 4 +-N (92.5 %), and PO 4 3–-P (80.7 %). Wastewater resources can be used to produce microbial protein for animal feed or organic fertiliser, conserving food chain resources. This investigation has employed the fermented sewage to photoheterotrophically grown purple non-sulfur bacteria (PNSB) in a 2.5 m3 pilot-scale raceway-pond with infrared light to produce proteinaceous biomass. Fermented sewage with synthetic media consisting of sodium acetate and propionic acids at a surface-to-volume (S/V) ratio of 10 m2/m3 removed 89%, 93%, and 81% of chemical oxygen demand, ammonium nitrogen, and orthophosphate, respectively; whereas respective removal in fermented sewage alone without synthetic media was 73%, 73%, and 72% during batch operation of 120 h. The biomass yield of 0.88–0.95 g COD biomass /g COD removed with protein content of 40.3 ± 0.3%–43.9 ± 0.2 % w/w was obtained for fermented sewage with synthetic media. The results revealed enhanced possibility of scaling-up the raceway reactor to recover resources from municipal wastewater and enable simultaneous high-rate PNSB single-cell protein production. [ABSTRACT FROM AUTHOR]

Microbial consortia consisting of phototrophs and heterotrophs have raised extensive attention due to their potential in sustainable biotechnology. The challenge remains in the selection of appropriate partners since most heterotrophic microorganisms cannot naturally use the intermediate carbohydrates secreted by autotrophic partners. In a recent study, the Ni Lab has developed a highly compatible autotrophic‐heterotrophic symbiotic system comprising Synechococcus elongatus and Vibrio natriegens. V. natriegens (the sucrose utilization module) shows a high degree of nutritional complementarity and culturing compatibility with the engineered S. elongatus (the CO2 sequestration module). The combination of both species channels CO2 into various valuable chemicals, enabling carbon‐negative biosynthesis. [ABSTRACT FROM AUTHOR]

Despite solid, growing genomic evidence for bacteria practicing bacteriochlorophyll and rhodopsin-based dual phototrophy, direct physiological proof has been lacking for over a decade until Kopejtka et al. recently solved the puzzle in an Alpine psychrophilic bacterium. Here, I highlight conceptual developments and address an overlooked, ecologically important phototrophic byproduct – heat. [ABSTRACT FROM AUTHOR]

Many eukaryotes acquired chloroplasts by endosymbiotic acquisition of photosynthetic bacteria or already-domesticated chloroplasts from other eukaryotes. However, the ciliate Mesodinium rubrum acquires the nucleus of a photosynthetic eukaryote, as well as its chloroplast, resulting in dramatic metabolic remodelling in the ciliate. [ABSTRACT FROM AUTHOR]

Hayashi et al. [[16]] reported the growth-promoting effect of lipopolysaccharide (LPS) from PNSB in plants for the first time, and the effective concentration of LPS from I Rhodobacter sphaeroides i was 10 pg/mL. The effective concentration of I R. sphaeroides i LPS for the plant was therefore approximately millions of times lower than those reported in previous studies. Lipid A, a domain of LPS, is a hydrophobic molecule that anchors LPS to the outer membrane of Gram-negative bacteria [[20]]. This Special Issue aims to contribute to the current knowledge in the field and promote the practical application of photosynthetic bacteria (PSB) biotechnology. [Extracted from the article]

Roseiflexus castenholzii is an ancient green non-sulfur bacteria that absorbs the solar energy through bacteriochlorophylls (BChls) bound in the only light harvesting (LH) complex, and transfers to the reaction center (RC), wherein primary charge separation occurs and transforms the energy into electrochemical potentials. In contrast to purple bacteria, R. castenholzii RC-LH (rcRC-LH) does not contain an H subunit. Instead, a tightly bound tetraheme cytochrome c subunit is exposed on the P-side of the RC, which contains three BChls, three bacteriopheophytins (BPheos), two menaquinones, and one iron for electron transfer. These novel structural features of the rcRC-LH are advantageous for enhancing the electron transfer efficiency and subsequent photo-oxidation of the c-type hemes. However, the photochemical properties of rcRC-LH and its applications in developing the photo-bioelectrochemical cells (PBECs) have not been characterized. Here, we prepared a PBEC using overlapped fluorine-doped tin oxide (FTO) glass and Pt-coated glass as electrodes, and rcRC-LH mixed with varying mediators as the electrolyte. Absence of the H subunit allows rcRC-LH to be selectively adhered onto the hydrophilic surface of the front electrode with its Q-side. Upon illumination, the photogenerated electrons directly enter the front electrode and transfer to the counter electrode, wherein the accepted electrons pass through the exposed c-type hemes to reduce the excited P+, generating a steady-state current of up to 320 nA/cm2 when using 1-Methoxy-5-methylphenazinium methyl sulfate (PMS) as mediator. This study demonstrated the novel photoelectric properties of rcRC-LH and its advantages in preparing effective PBECs, showcasing a potential of this complex in developing new type PBECs.

We investigate the applicability of the linearized semiclassical initial value representation (LSCIVR) method to excitation energy transfer (EET) problems in molecular aggregates by simulating the EET dynamics of a dimer model in a wide range of parameter regime and comparing the results to those obtained from a numerically exact method. It is found that the LSC-IVR approach yields accurate population relaxation rates and decoherence rates in a broad parameter regime. However, the classical approximation imposed by the LSC-IVR method does not satisfy the detailed balance condition, generally leading to incorrect equilibrium populations. Based on this observation, we propose a post-processing algorithm to solve the long time equilibrium problem and demonstrate that this long-time correction method successfully removed the deviations from exact results for the LSC-IVR method in all of the regimes studied in this work. Finally, we apply the LSC-IVR method to simulate EET dynamics in the photosynthetic Fenna-Matthews-Olson complex system, demonstrating that the LSC-IVR method with long-time correction provides excellent description of coherent EET dynamics in this typical photosynthetic pigment-protein complex. [ABSTRACT FROM AUTHOR]

Microbial electric syntrophy, involving direct electron transfer between electron-donating strains and electron-accepting strains, could reduce more than 50% of methane emissions and remove 90% of nitrate pollution in some wastewaters. Microbial electric syntrophy is also a key natural process allowing the survival of bacteria in harsh environmental conditions. Here we review natural and artificial cases of interspecies electron transfer in microbial syntrophy, with emphasis on methane production, electroactive bacteria, methanogens, anaerobic methane-oxidizing consortia, Geobacter species, phototrophic bacteria, co-cultures, anaerobic digestion, environmental remediation and microbial electrosynthesis. Environmental remediation includes nitrogen removal, reductive dechlorination and pollutant degradation. Microbial electrosynthesis can be used for carbon dioxide reduction. Conductive proteins and materials, and light-assisted electron transfer contribute to the direct interspecies electron transfer. [ABSTRACT FROM AUTHOR]

This study investigates the microbiologically influenced corrosion (MIC) of X80 steel accelerated by the phototrophic bacterium Rhodopseudomonas palustris TIE-1. The photorespiration plays a key role in promoting extracellular electron transfer (EET)-induced MIC. In the early corrosion stage, unstable localized corrosion dominated in the dark, while intense diffusion-controlled corrosion occurs in light. Compared to the sterile anaerobic medium, R. palustris TIE-1 accelerated corrosion of X80 steel, with a significantly higher corrosion rate under light conditions, approximately three times that of dark conditions. Inhibition of photosynthetic electron transfer or cessation of photostimulation resulted in pronounced reduction in the corrosion rate. • MIC of X80 steel by R. palustris TIE-1 can be accelerated by light-driven EET. • The R. palustris TIE-1 induced predominant localized corrosion under light but uniform corrosion in the dark. • Inhibition of photorespiration or cessation of light significantly reduced MIC. [ABSTRACT FROM AUTHOR]

Purple phototrophic bacteria possess light-harvesting 1 and reaction center (LH1-RC) core complexes that play a key role in converting solar energy to chemical energy. High-resolution structures of LH1-RC and RC complexes have been intensively studied and have yielded critical insight into the architecture and interactions of their proteins, pigments, and cofactors. Nevertheless, a detailed picture of the structure and assembly of LH1-only complexes is lacking due to the intimate association between LH1 and the RC. To study the intrinsic properties and structure of an LH1-only complex, a genetic system was constructed to express the Thermochromatium (Tch.) tepidum LH1 complex heterologously in a modified Rhodospirillum rubrum mutant strain. The heterologously expressed Tch. tepidum LH1 complex was isolated in a pure form free of the RC and exhibited the characteristic absorption properties of Tch. tepidum. Cryo-EM structures of the LH1-only complexes revealed a closed circular ring consisting of either 14 or 15 αβ-subunits, making it the smallest completely closed LH1 complex discovered thus far. Surprisingly, the Tch. tepidum LH1-only complex displayed even higher thermostability than that of the native LH1-RC complex. These results reveal previously unsuspected plasticity of the LH1 complex, provide new insights into the structure and assembly of the LH1-RC complex, and show how molecular genetics can be exploited to study membrane proteins from phototrophic organisms whose genetic manipulation is not yet possible. • Thermochromatium tepidum LH1-only complex was heterologously expressed in a modified Rhodospirillum rubrum mutant strain. • The LH1-only complex was a closed circular ring consisting of either 14 or 15 αβ-subunits and its structure was resolved using cryo-EM. • LH1-only complex displayed even higher thermostability than that of the native LH1-RC complex. [ABSTRACT FROM AUTHOR]

The rates, yields, mechanisms and directionality of electron transfer (ET) are explored in twelve pairs of Rhodobacter (R.) sphaeroides and R. capsulatus mutant RCs designed to defeat ET from the excited primary donor (P*) to the A-side cofactors and re-direct ET to the normally inactive mirror-image B-side cofactors. In general, the R. sphaeroides variants have larger P+H B − yields (up to ∼90%) than their R. capsulatus analogs (up to ∼60%), where H B is the B-side bacteriopheophytin. Substitution of Tyr for Phe at L-polypeptide position L181 near B B primarily increases the contribution of fast P* → P+B B − → P+H B − two-step ET, where B B is the "bridging" B-side bacteriochlorophyll. The second step (∼6–8 ps) is slower than the first (∼3–4 ps), unlike A-side two-step ET (P* → P+B A − → P+H A −) where the second step (∼1 ps) is faster than the first (∼3–4 ps) in the native RC. Substitutions near H B , at L185 (Leu, Trp or Arg) and at M-polypeptide site M133/131 (Thr, Val or Glu), strongly affect the contribution of slower (20–50 ps) P* → P+H B − one-step superexchange ET. Both ET mechanisms are effective in directing electrons "the wrong way" to H B and both compete with internal conversion of P* to the ground state (∼200 ps) and ET to the A-side cofactors. Collectively, the work demonstrates cooperative amino-acid control of rates, yields and mechanisms of ET in bacterial RCs and how A- vs. B-side charge separation can be tuned in both species. [Display omitted] • Cooperative amino-acid control of electron transfer mechanisms in proteins. • Constructed twelve pairs of R. sphaeroides and R. capsulatus mutant reaction centers. • Ultrafast studies of rates, yields, mechanisms & directionality of electron transfer. • Higher yield of wrong way electron transfer to H B in R. sphaeroides vs. R. capsulatus. • Both one- and two-step electron transfer are effective in reducing H B in both species. [ABSTRACT FROM AUTHOR]

Light-induced electron flow between reaction center and cytochrome bc 1 complexes is mediated by quinones and electron donors in purple photosynthetic bacteria. Upon high-intensity excitation, the contribution of the cytochrome bc 1 complex is limited kinetically and the electron supply should be provided by the pool of reduced electron donors. The kinetic limitation of electron shuttle between reaction center and cytochrome bc 1 complex and its consequences on the photocycle were studied by tracking the redox changes of the primary electron donor (BChl dimer) via absorption change and the opening of the closed reaction center via relaxation of the bacteriochlorophyll fluorescence in intact cells of wild type and pufC mutant strains of Rubrivivax gelatinosus. The results were simulated by a minimum model of reversible binding of different ligands (internal and external electron donors and inhibitors) to donor and acceptor sides of the reaction center. The calculated binding and kinetic parameters revealed that control of the rate of the photocycle is primarily due to 1) the light intensity, 2) the size and redox state of the donor pool, and 3) the unbinding rates of the oxidized donor and inhibitor from the reaction center. The similar kinetics of strains WT and pufC lacking the tetraheme cytochrome subunit attached to the reaction center raise the issue of the physiological importance of this subunit discussed from different points of view. A crucial factor for the efficacy of electron donors in photosynthetic photocycle is not just the substantial size of the pool and large binding affinity (small dissociation constant K D = k off / k on) to the RC, but also the mean residence time (k off)−1 in the binding pocket. This is an important parameter that regulates the time of re-activation of the RC during multiple turnovers. The determination of k off has proven challenging and was performed by simulation of widespread experimental data on the kinetics of P+ and relaxation of fluorescence. This work is a step towards better understanding the complex pathways of electron transfer in proteins and simulation-based design of more effective electron transfer components in natural and artificial systems. • Cooperative redox control of electron transfer mechanisms in proteins. • Continuous and strong illumination drives the photocycle without cyt bc 1 complex. • The rate of photocycle depends on the size and redox poise of the periplasmic donor pool. • The natural electron donors have similar binding affinities to the tetraheme cytochrome and to the reaction center. • Ligands to both sides of the reaction center limit the rate of the photocycle. [ABSTRACT FROM AUTHOR]

Hydraulic mixing of stratified reservoirs homogenizes physicochemical gradients and microbial communities. This has potential repercussions for microbial metabolism and water quality, not least in dams and hydraulically controlled waters. A better understanding of how key taxa respond to mixing of such stratified water bodies is needed to understand and predict the impact of hydraulic operations on microbial communities and nutrient dynamics in reservoirs. We studied taxa transitions between cyanobacteria and sulfur-transforming bacteria following mixing of stratified water columns in bioreactors and complemented the experimental approach with a biogeochemical model. Model predictions were consistent with experimental observations, suggesting that stable stratification of DO is restored within 24 h after episodic and complete mixing, at least in the absence of other more continuous disturbances. Subsequently, the concentration of S2− gradually return to pre-mixing states, with higher concentration at the surface and lower in the bottom waters, while the opposite pattern was seen for SO 4 2−. The total abundance of sulfate-reducing bacteria and phototrophic sulfur bacteria increased markedly after 24h of mixing. The model further predicted that the rapid re-oxygenation of the entire water column by aeration will effectively suppress the water stratification and the growth of sulfur-transforming bacteria. Based on these results, we suggest that a reduction of thermocline depth by optimal flow regulation in reservoirs may also depress sulfur transforming bacteria and thereby constrain sulfur transformation processes and pollutant accumulation. The simulation of microbial nutrient transformation processes in vertically stratified waters can provide new insights about effective environmental management measures for reservoirs. [Display omitted] • Stable DO stratification was restored within 24h after episodic mixing. • Sulfur-transforming bacteria increased in abundance after re-stratification and stratified over depth. • Rapid re-oxygenation of whole water by aeration can suppress the growth of sulfur-transforming bacteria. • Reducing thermocline depth by optimal reservoir flow regulation process may also depress sulfur-transforming bacteria. [ABSTRACT FROM AUTHOR]

[Display omitted] • Zinc 31-demethyl-bacteriochlorophylls- d with pinacol boronate on B-ring were prepared. • The synthetic analogs self-aggregated in aqueous micelles similar to chlorosome. • The chlorosome-like aggregates exhibited red-shifted and broadened Qy bands. • Exciton-coupled circular dichroism couplets were observed in the red-shifted regions. • The J-aggregation suppressed with an increase in the size of the boron substituents. Zinc 3-hydroxymethyl-131-oxo-bacteriochlorins possessing a variety of pinacol boronates on the B-ring were prepared from chemical modification of naturally occurring chlorophyll- a. The synthetic bacteriochlorophyll- d analogs were dissolved into an aqueous Triton X-100 solution to exhibit red-shifted and broadened electronic absorption bands with reversed S-shape circular dichroism bands, compared with their monomeric bands. The behaviors indicated that most synthetic models possessing a bacteriochlorin π-system self-aggregated inside the aqueous micelles to give similar oligomers as the J-aggregates of bacteriochlorophyll- d bearing a chlorin π-skeleton in major light-harvesting antennas of green photosynthetic bacteria, chlorosomes. The methylboronate self-aggregated more largely than the phenylboroante, and the self-aggregation was suppressed by ortho -substitution on the phenyl ring: phenyl > 1-naphthyl ≫ 9-anthryl and phenyl > 2,6-dimethylphenyl. Along with an increase in the size of the substituents on the boron atom of their boronates, the formation of the chlorosome-like self-aggregates decreased substantially. [ABSTRACT FROM AUTHOR]

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 CO 2 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. In this study, a simple air-cathode MFC dominated by purple non-sulfur bacteria (PNSB) was constructed to investigate the effect of light, COD concentration and microbial community on its electricity generation and OM degradation, which can provide a theoretical guidance for the long-term stability of application of PNSB-MFC. [Display omitted] • Indirect/direct electron transport is revealed under light and dark, respectively. • Light condition is beneficial to OM degradation rather than electricity generation. • Dark condition can increase the diversity of electrogenic bacteria. • PNBS-MFC has better power generation performance in low COD concentration. [ABSTRACT FROM AUTHOR]

Bioelectrochemical systems have been used to enhance the carbon sequestration of photosynthetic bacteria (PSB), but it is unclear whether the electrical stimulation affects the structure of membrane proteins involved in photochemical activity. In this study, the rate of CO 2 fixation in the photosynthetic bacteria R. palustris increased with electrical stimulation, and the enhancement partly remained even after the power off. The CO 2 fixation rate in electrical-stimulated PSB was 10% higher than in non-stimulated PSB, and the activity of the CO 2 fixation enzyme Rubisco was 16% higher. This resulted from the improved light utilization efficiency of the photosynthetic units in R. palustris after electrical stimulation, particularly due to the enhancement of the primary reaction mediated by the light capture protein RC-LH1. The molar extinction coefficient of the light capture protein RC-LH1 increased from 3301 cm−1 mM−1 to 3733 cm−1 mM−1, and the maximum rate of the primary reaction increased from 6.88 × 10−3 e−RC−1s−1 to 8.66 × 10−3 e−RC−1s−1. Circular dichroism spectroscopy and Fourier transform infrared spectroscopy indicated that the electrical stimulation increased the dipole moment of the α-helix in RC-LH1 to facilitate the quinone transport in the primary reaction. Nuclear magnetic resonance spectroscopy revealed that the electrical stimulation increased the formation of hydrogen bonds in bacteriochlorophyll a for electron transition. This study investigated the response of photosynthetic bacteria to electrical stimulation, providing a distinct outlook on the electrochemical regulation of photosynthesis for carbon capture. [Display omitted] • Photosynthetic bacteria fixed CO 2 more efficiently even under power off. • Photochemical activity of RC-LH1 in photosynthetic units was improved. • Electrical stimulation changed the structure of RC-LH1 in photosynthetic unit. • Up-regulated protein W expression benefits the quinone transport in RC-LH1. • Increased hydrogen bond formation accelerated the electron transition in BChl a. [ABSTRACT FROM AUTHOR]

• Reducing power allocation varies with different ammonia loading. • Under ammonia limited conditions, PHA and H 2 production compete for reducing power. • After PHA accumulation reached saturation, H 2 generation dominated. • Under ammonia limited conditions, TCA cycle was more active. • In N-limited cases, PHA, H 2 production and CO 2 fixation genes were highly activated. The global energy crisis has intensified the search for sustainable and clean alternatives, with biohydrogen emerging as a promising solution to address environmental challenges. Leveraging photo fermentation (PF) process, purple phototrophic bacteria (PPB) can harness reducing power derived from organic substrates to facilitate hydrogen production. However, existing studies report much lower H 2 yields than theoretical value when using acetate as carbon source and ammonia as nitrogen source, primarily attributed to the widely employed pulse-feeding mode which suffers from ammonia inhibition effect on nitrogenase. To address this issue, a continuous feeding mode was applied to avoid ammonia accumulation in this study. On the other hand, other pathways like carbon fixation and polyhydroxyalkanoate (PHA) formation could compete reducing power with H 2 production. However, the reducing power allocation under continuous feeding mode is not yet clear. In this study, the reducing power allocation and hydrogen production performance were evaluated under various ammonia loading, using acetate as carbon source and infrared LED at around 50 W·m−2 as light source. The results show that (a) The absence of ammonia resulted in the best performance for hydrogen production, with 44 % of the reducing power distributed to H 2 and the highest H 2 volumetric productivity, while the allocation of reducing power to hydrogen production stopped when ammonia loading was above 7.6 mg NH 4 -N·L−1·d−1; (b) when PPB required to eliminate reducing power under ammonia limited conditions, PHA production was the preferred pathway followed by the hydrogen production pathway, but once PHA accumulation reached saturation, hydrogen generation pathway dominated; (c) under ammonia limited conditions, the TCA cycle was more activated rendering higher NADH (i.e. reducing power) production compared with that under ammonia sufficient conditions which was verified by metagenomics analysis, and all the hydrogen production, PHA accumulation and carbon fixation pathways were highly active to dissipate reducing power. This work provides the insight of reducing power distribution and PPB biohydrogen production variated by ammonia loading under continuous feeding mode. [Display omitted] [ABSTRACT FROM AUTHOR]

Simple Summary: Marine sponges contain associated microorganisms in high numbers. This study gives insight into how environmental conditions such as light availability affects the symbiotic relationship between phototrophic bacteria that obtain energy from sunlight for the synthesis of organic compounds and the marine host in which they are found. A controlled aquarium experiment with defined light levels ranging from darkness to higher light intensity demonstrates how light conditions change the number of these bacteria and, consequently, host performance. Sponge growth performance was significantly affected by the number of these bacteria. Moreover, the common blue aquarium sponge Lendenfeldia chondrodes has proven to be perfectly suited as a model organism to study marine host-symbiont interactions. Bacterial symbionts in marine sponges play a decisive role in the biological and ecological functioning of their hosts. Although this topic has been the focus of numerous studies, data from experiments under controlled conditions are rare. To analyze the ongoing metabolic processes, we investigated the symbiosis of the sponge specific cyanobacterium Synechococcus spongiarum and its sponge host Lendenfeldia chondrodes under varying light conditions in a defined aquarium setting for 68 days. Sponge clonal pieces were kept at four different light intensities, ranging from no light to higher intensities that were assumed to trigger light stress. Growth as a measure of host performance and photosynthetic yield as a proxy of symbiont photosynthetic activity were measured throughout the experiment. The lack of light prevented sponge growth and induced the expulsion of all cyanobacteria and related pigments by the end of the experiment. Higher light conditions allowed rapid sponge growth and high cyanobacteria densities. In addition, photosynthetically active radiation above a certain level triggered an increase in cyanobacteria's lutein levels, a UV absorbing protein, thus protecting itself and the host's cells from UV radiation damage. Thus, L. chondrodes seems to benefit strongly from hosting the cyanbacterium S. spongiarum and the relationship should be considered obligatory mutualistic. [ABSTRACT FROM AUTHOR]

In the thylakoid membrane of cyanobacteria and chloroplasts, many proteins involved in photosynthesis are associated with or integrated into the fluid bilayer matrix formed by four unique glycerolipid classes, monogalactosyldiacylglycerol, digalactosyldiacylglycerol, sulfoquinovosyldiacylglycerol, and phosphatidylglycerol. Biochemical and molecular genetic studies have revealed that these glycerolipids play essential roles not only in the formation of thylakoid lipid bilayers but also in the assembly and functions of photosynthetic complexes. Moreover, considerable advances in structural biology have identified a number of lipid molecules within the photosynthetic complexes such as PSI and PSII. These data have provided important insights into the association of lipids with protein subunits in photosynthetic complexes and the distribution of lipids in the thylakoid membrane. Here, we summarize recent high-resolution observations of lipid molecules in the structures of photosynthetic complexes from plants, algae, and cyanobacteria, and evaluate the distribution of lipids among photosynthetic protein complexes and thylakoid lipid bilayers. By integrating the structural information into the findings from biochemical and molecular genetic studies, we highlight the conserved and differentiated roles of lipids in the assembly and functions of photosynthetic complexes among plants, algae, and cyanobacteria. [ABSTRACT FROM AUTHOR]

The intestinal microbiota of marine animals was influenced by the water and environment in which they live. The Amur ide (Leuciscus waleckii) adapts to extremely high alkalinity and is an ideal material for aquacultural studies of alkaline adaptation. In this study, we screened intestinal indicator flora and functional redundancy of intestinal colonies in alkaline-water species (AW) and freshwater species (FW) of Amur ide (L. waleckii) in these different aquatic environments. The available vs. community composition correlations were then predicted by contrasting each other with the flora contained in environmental water samples. Here, five microbial species and six genera were identified owing to the classifiable sequence. The intestinal microbiota that existed in AW and FW had approximately 1/3 of the operational taxonomic units in the respective living water environments, meaning gut microbes in the aqueous habitats will have an influential association with gut microbes in AW and FW. Compared to the bacterial composition of the FW intestine and that present in freshwater, Moraxella osloensis, Psychrobacter maritimus , and Psychrobacter faecalis were significantly enriched in the intestine of AW and alkaline water samples. In the FW intestine and freshwater samples, however, Cryptomonas curvata and Polynucleobacter asymbioticus were highly improved, which can be summarized as Enterobacter sp., the predominant population in the AW gut, while Aeromonas and Ralstonia being primarily present in FW intestines. Photosynthetic bacteria were most significant in both water samples. The results indicated that the intestinal microbiota composition, abundance, and diversity of AW and FW were quite different. In contrast, the microbial composition of the additional alkaline water and freshwater environments showed slight differences. This study expects to enhance our understanding of the alkalinity tolerance of L. waleckii , which will be provided for the breeding of fish living in alkaline water, and push the development of alkaline water resources with increased efficiency. [ABSTRACT FROM AUTHOR]

• External potential enhanced MNZ removal by C. vulgaris - R. Palustris co-culture. • 0 V led to the highest photosynthetic current intensity and fastest MNZ removal. • MNZ removal rate was positively related to photosynthetic current intensity. • Photosynthetic electron extraction enhanced C. vulgaris - R. Palustris synergism. • Accumulation of tryptophan, tyrosine and humic acid accelerated MNZ removal. 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. [Display omitted] [ABSTRACT FROM AUTHOR]

Wastewater reuse for agricultural irrigation still raises important public health issues regarding its safety, due to the increasing presence of emerging contaminants, such as antibiotic resistant bacteria and genes, in the treated effluents. In this paper, the potential for a commercial Desal 5 DK nanofiltration membrane to be used as a tertiary treatment in the wastewater treatment plants for a more effective elimination of these pollutants from the produced effluents was assessed on laboratory scale, using a stainless steel cross-flow cell. The obtained results showed high concentrations of total bacteria and target carbapenem and (fluoro)quinolone resistance genes (blaKPC, blaOXA-48, blaNDM, blaIMP, blaVIM, qnrA, qnrB and qnrS) not only in the discharged, but also in the reused, effluent samples, which suggests that their use may not be entirely safe. Nevertheless, the applied nanofiltration treatment achieved removal rates superior to 98% for the total bacteria and 99.99% for all the target resistance genes present in both DNA and extracellular DNA fractions, with no significant differences for these microbiological parameters between the nanofiltered and the control tap water samples. Although additional studies are still needed to fully optimize the entire process, the use of nanofiltration membranes seems to be a promising solution to substantially increase the quality of the treated wastewater effluents. [ABSTRACT FROM AUTHOR]

Halorhodospira (Hlr.) species are the most halophilic and alkaliphilic of all purple bacteria. Hlr. halochloris exhibits the lowest LH1 Qy transition energy among phototrophic organisms and is the only known triply extremophilic anoxygenic phototroph, displaying a thermophilic, halophilic, and alkaliphilic phenotype. Recently, we reported that electrostatic charges are responsible for the unusual spectroscopic properties of the Hlr. halochloris LH1 complex. In the present work, we examined the effects of salt and pH on the spectroscopic properties and thermal stability of LH1-RCs from Hlr. halochloris compared with its mesophilic counterpart, Hlr. abdelmalekii. Experiments in which the photocomplexes were subjected to different levels of salt or variable pH revealed that the thermal stability of LH1-RCs from both species was largely retained in the presence of high salt concentrations and/or at alkaline pH but was markedly reduced by lowering the salt concentration and/or pH. Based on the amino acid sequences of LH1 polypeptides and their composition of acidic/basic residues and the Hofmeister series for cation/anion species, we discuss the importance of electrostatic charge in stabilizing the Hlr. halochloris LH1-RC complex to allow it to perform photosynthesis in its warm, hypersaline, and alkaline habitat. [ABSTRACT FROM AUTHOR]

Among purple photosynthetic bacteria, the transcription factor CrtJ is a major regulator of photosystem gene expression. Depending on growing conditions, CrtJ can function as an aerobic repressor or an anaerobic activator of photosystem genes. Recently, CrtJ's activity was shown to be modulated by two size variants of a B12 binding co-regulator called SAerR and LAerR in Rhodobacter capsulatus. The short form, SAerR, promotes CrtJ repression, while the longer variant, LAerR, converts CrtJ into an activator. In this study, we solved the crystal structure of R. capsulatus SAerR at a 2.25 Å resolution. Hydroxycobalamin bound to SAerR is sandwiched between a 4-helix bundle cap, and a Rossman fold. This structure is similar to a AerR-like domain present in CarH from Thermus termophilus, which is a combined photoreceptor/transcription regulator. We also utilized AlphaFold software to predict structures for the LAerR, CrtJ, SAerR-CrtJ and LAerR-CrtJ co-complexes. These structures provide insights into the role of B12 and an LAerR N-terminal extension in regulating the activity of CrtJ. [ABSTRACT FROM AUTHOR]

Heliomicrobium modesticaldum has been used as a model organism for the Heliobacteria, the only phototrophic family in the Firmicutes. It is a moderately thermophilic anoxygenic phototrophic bacterium that is capable of fermentative growth in the dark. The genetic manipulation of H. modesticaldum is still in its infancy. Methods to introduce genes through the use of exogenous plasmids and to delete genes from the chromosome through the use of the native CRISPR/Cas system have been developed in the last several years. To expand our genetic toolkit, it was necessary to control gene expression. In this study, we analyzed constitutive and inducible promoters developed for clostridia for their use in H. modesticaldum and further tested two reporters, adhB and lacZ, as indicators of promoter strength. Alcohol dehydrogenase (AdhB) was unsuitable as a reporter in this species due to high endogenous activity and/or low activity of the reporter, but a thermostable LacZ worked well as a reporter. A set of constitutive promoters previously reported to work in Clostridium thermocellum was found to be reliable for controlling the expression of the lacZ reporter gene in H. modesticaldum at a range of activities spanning an order of magnitude. An anhydrotetracycline-inducible promoter was created by inserting tetO operators into a strong constitutive promoter, but it was not fully repressible. The implementation of a xylose-inducible promoter resulted in complete repression of β-gal in the absence of xylose, and reliable expression tunable through the concentration of xylose added to the culture. [ABSTRACT FROM AUTHOR]

Photosystem II is a light-driven water-plastoquinone oxidoreductase present in cyanobacteria, algae and plants. It produces molecular oxygen and protons to drive ATP synthesis, fueling life on Earth. As a multi-subunit membrane-protein-pigment complex, Photosystem II undergoes a dynamic cycle of synthesis, damage, and repair known as the Photosystem II lifecycle, to maintain a high level of photosynthetic activity at the cellular level. Cyanobacteria, oxygenic photosynthetic bacteria, are frequently used as model organisms to study oxygenic photosynthetic processes due to their ease of growth and genetic manipulation. The cyanobacterial PSII structure and function have been well-characterized, but its lifecycle is under active investigation. In this review, advances in studying the lifecycle of Photosystem II in cyanobacteria will be discussed, with a particular emphasis on new structural findings enabled by cryo-electron microscopy. These structural findings complement a rich and growing body of biochemical and molecular biology research into Photosystem II assembly and repair. [ABSTRACT FROM AUTHOR]

The production of hydrogen using microorganisms is an environment-friendly and less energy-intensive way of producing hydrogen. Rhodoplanes piscinae is a photosynthetic bacterium with the ability of hydrogen production under photosynthetic conditions. In this study, a new strain 51ATA was isolated from Lake Akkaya, Nigde, Turkey that is exposed to some industrial effluent charges. The new strain was identified as R. piscinae by phylogenetic analysis of the 16S ribosomal DNA (rDNA) sequence. The quality of molasses as a substrate for hydrogen production was evaluated by comparing it with other substrates, such as glucose and acetate. Five different culture media of various concentrations (1.0 g/L, 2.0 g/L, 5.0 g/L, 10 g/L, and 20 g/L) for each substrate were used. Results have shown that molasses was the best substrate for the biohydrogen production. The highest amount of biohydrogen obtained from each (20 g/L) substrate was (1.27 L H 2 /L from molasses-containing culture), (0.72 L H 2 /L from glucose-containing culture), and acetate-containing culture (0.21 L H 2 /L) respectively. From these results, we could conclude that R.piscinae 51ATA strain is as good as the other bacterial species used for hydrogen production and may be considered as a high potential strain for hydrogen production when used in combination with molasses under phototrophic conditions. • A new photosynthetic bacterial strain 51ATA of Rhodoplanes piscinae was observed hydrogen production. • Molasses was determined the best co-substrate for R.piscinae compared to acetate and glucose in hydrogen production. • As a co substrate, acetate promoted biomass production not hydrogen production. [ABSTRACT FROM AUTHOR]