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Growing concerns over greenhouse gas emissions and energy insecurity caused by the depletion of conventional fuels have led to a search for sustainable fuel alternatives. As an alternative energy carrier, hydrogen (H 2) is particularly attractive as only water is released during combustion. The process of H 2 production from genetically engineered phototrophic microorganisms through biophotolysis leads the way to solve energy shortages. Genetically engineered cyanobacteria species are potential candidates due to their superior properties for reducing greenhouse gases and using solar energy as an energy source. The review discusses the mechanisms and enzymes involved in H 2 production by cyanobacteria and applications of genetic engineering. A critical analysis of the fundamental issues attributed to the technical advancement of photobiological cyanobacteria-based H 2 production is provided, as well as the perspectives for future research to reduce carbon dioxide emissions through the creation of waste-free technology. • Genetic engineering findings of cyanobacterial nitrogenase enzyme are described. • Recent genetic engineering methods to obtain hydrogenase mutants are discussed. • Engineering photosynthetic H 2 production is shown as an efficient method. • Development of a non-waste H 2 production technology is explained. [ABSTRACT FROM AUTHOR]

Among multiple alternative clean and renewable energy sources, hydrogen is the most promising green fuel because of its high conversion efficiency, energy potentiality, and sustainability. In this review, green biohydrogen production by anoxygenic photosynthetic bacteria (APB) is summarized with the aim to enhance the present understanding of the underlying mechanisms and to gain a definite presentation of the current state of biohydrogen production. Mechanisms of biohydrogen derived from APB are briefly summarized, including the transformation of light energy into adenosine triphosphate, the metabolism of organic matter producing hydrogen ions, and photosynthetic bacteria coupled with reducing substances. In addition, factors affecting biohydrogen production by APB, including internal factors and external factors, are systematically described and discussed. Moreover, current methods for improving the hydrogen production efficiency from APB are presented. Promising applications ingratiating sustainable development goals are summarized, and both economic viability and environmental sustainability are reviewed. [Display omitted] • Anoxygenic photosynthetic bacteria (APB) do not evolve O 2 in hydrogen production. • APB consume organic substrates and produce hydrogen at high rates. • ATP serving as co-factor participate in nitrogenase-catalyzed hydrogen evolution. • APB can yield carotenoid as by-products during the process of hydrogen production. • More high-quality life cycle assessment studies should be performed in the future. [ABSTRACT FROM AUTHOR]

Strategy to improve single-stage photofermentative hydrogen productivity of photosynthetic bacteria (PSB) by efficient use a formulated lignocellulosic substrate through suitable supplement of iron and molybdenum as enhancers of microbial activity of R. palustris was proposed. The maximum hydrogen production rate of 48.1 ml h−1 L−1 was obtained using response surface methodology as the result of accelerated bioreaction of proton reduction under inoculum density of 118.1 mg L−1, Fe2+ of 13.2 mg L−1 and Mo6+ of 2.65 μg L−1. Biokinetic analysis revealed the enhanced microbial activities in biomass synthesis and H 2 production. Suitable metal addition enabled PSB to act in whole as biocatalyst to facilitate assimilation of the formulated electron-rich carbon source from wheat straw through the efficient electron transfer needed for both cell growth and enzyme function of nitrogenase. Therefore, higher kinetic values of k c in 0.146 h−1 and R m in 59.4 ml h−1 L−1, accompanied with improved performances of H 2 yield in 1.56 mol mol−1 carbon and substrate degradation in 93.6% were attained. [Display omitted] • Enhancement strategy of lignocellulosic photofermentation was developed. • A higher production rate of 48.1 ml H 2 h−1 l−1 from wheat straw was attained by R. palustris. • Synergistic effect of metal Fe and Mo addition stimulated nitrogenase-catalyzed H 2 reaction. [ABSTRACT FROM AUTHOR]

NifA is the primary activator of nitrogenase, and the N-terminal domain of nifA is sensitive to ammonium concentration. In this work, a mutant Rhodobacter capsulatus ZX01 with a genetically engineered deletion in the N-terminal region of nifA1 was constructed by employing overlap extension PCR to mitigate the inhibition of ammonium on nitrogenase expression in photosynthetic bacteria. The effects of different ammonium ion concentrations on the growth and photo-fermentative hydrogen production performance of wild-type strain R. capsulatus SB1003 and mutant ZX01 with glucose and volatile fatty acids as the carbon sources were studied, respectively. When the ratio of NH 4 +-N was 20% and 30%, the hydrogen yield of the mutant ZX01 was enhanced by 14.8% and 20.9% compared with that of R. capsulatus SB1003 using 25 mM acetic acid and 34 mM butyric acid as the carbon source, respectively. In comparison, using 30 mM glucose as the carbon source, the hydrogen yield of ZX01 was increased by 17.7% and 22.2% compared with that of R. capsulatus SB1003 when the ratio of NH 4 +-N was 20% and 30%, and the nitrogenase activity of ZX01 was also enhanced by 38.0% and 47.6%, respectively. When using 10 mM NH 4 + as a single nitrogen source, ZX01 showed a 2.6-fold increase in H 2 production. These results indicated that ZX01 demonstrated higher ammonium tolerance and better hydrogen production performance than the wild-type. The deletion in the N-terminal region of nifA1 could partially de-repress the nitrogenase activity inhibited by ammonium. [Display omitted] • The mutant with a deletion in the N-terminal region of nifA1 was constructed by overlap extension PCR. • The deletion in the N-terminal of nifA1 appeared to partially derepress the NH 4 + inhibition on nitrogenase activity. • The H 2 yield of ZX01 was increased by up to 22.3% compared with that of wild-type in the presence of ammonium. [ABSTRACT FROM AUTHOR]

Photo-fermentative hydrogen production rate improving has been a key limiting link in the field of biological hydrogen production by photosynthetic bacterium (PSB) in recent years. In our previous study, apparent hydrogen production enhancement was observed in R. sphaeroides HY01 with tetA expressed under tetracycline (Tc), which attracted our interests. It was found that Tc-resistant strains always presented stable hydrogen production promotion on the maximum hydrogen production rate (R m), which was approximately 30% with Tc addition. Figuring out the underlying connections between Tc resistance and hydrogen production of R. sphaeroides may provide new methods for obtaining engineered PSB with high hydrogen production performance. In this study, basing on experimental tests, hydrogen promotion of resistant strain was found to be Tc dose-dependent. Some relevant gene expression differences on hydrogen production of Rodobacter sphaeroides induced by the expression of TetA and the addition of Tc were also tested and discussed. [Display omitted] • Apparent H 2 production enhancement was observed in tetA expressing mutants under Tc. • The promotion on H 2 production was found to be Tc concentration dependent. • Significant gene expression differences of resistant strains presented under Tc. • Synergistic promoting effects may exist between Tc transport and H 2 production. [ABSTRACT FROM AUTHOR]

The biohydrogen production is promising for the alternative green hydrogen. The two-stage of the dark and photo-fermentation system increases the hydrogen production yield. In this study, the experiments carried out the cell immobilizations on dark and photo bacteria; and liquid suspended photo bacteria for those two-stage batch systems. The optimized parameters obtained, such as materials for immobilized cells, different substrates, and the substrate concentrations for hydrogen fermentation. The experiment results showed pure substrate glucose could produce a higher amount of hydrogen in the photo immobilized cells, the hydrogen concentration was up to about 40%, the utilization rate of glucose was as high as 99.41%, the accumulated hydrogen volume was 169.13 mL, and the hydrogen yield, HY, was 0.63 mol H 2 /mol glucose. In addition, the activated immobilized cells are used for two-stage fermentation to generate hydrogen, HY 1.75 mol H 2 /mol substrate. The two-stage batch fermentations for producing hydrogen, used the Gompertz equation model to obtain the cumulative hydrogen volume and hydrogen production rate (HPR). When the ratio of dark immobilized cells (DIMC) to photo suspended liquids (PSL) is 1.0:5.0, the hydrogen production shows well performance. Moreover, an advanced molecular biological technique, next-generation sequencing (NGS) with ultra-high-throughput DNA output, was applied to perform microbial communities in a different stage of hydrogen fermentation. The NGS help to understand the detailed microbial community change in such fermentation processes and provide better biological efficacy via clarifying the role of microorganisms and their interactions. After the experiments, the Clostridia increased to 28%, and the Enterobacter also increased to 15%, therefore the Rhodobacter and Bosea were reduced from 55% to 17%. Understand the detailed composition of microbial populations in stages of such bio-system will provide the useful information via clarify the biological role of microorganisms and its interactions. [Display omitted] • The study successfully made the immobilized cells of photosynthetic bacteria in batch reactors. • Photo-immobilized cells obtained the best hydrogen production of 169.13 mL H 2 /100 mL. • The microbial community of photo-immobilized cells changed significantly before and after the experiments. • The next-generation sequencing technique provides the relations of microbial and H 2 production. • Immobilized cells applied to two-stage of dark/photo H 2 productions obtained good outcomes. [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]

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. [Display omitted] • Modelling biomass growth and biohydrogen production of Rhodopseudomonas palustris. • Unified influences of light intensity, light attenuation and temperature. • Perturbation analysis for evaluating model accuracy and reliability. • Acceptable extrapolations for two different Photobioreactor (PBR) scales and sizes. • Embedding light/dark cycles and biohydrogen partial pressure onto PBR performance. [ABSTRACT FROM AUTHOR]

In this study, Rubrivivax benzoatilyticus JA2T (=ATCC BAA-35T = JCM 13220T = MTCC 7087T), an anoxygenic photosynthetic bacterium, was subjected to altered conditions and observed for changes in power outcome in the two chambered microbial fuel cells (MFCs), the basis of which was established using metabolomic studies. This is an extension to our previous studies, which showed that, under photo heterotrophic conditions, glucose in the form of a solitary carbon resource in minimal media, caused the strain JA2 to exhibit altered growth rates, progressive loss of pigmentation and reduced cell size (3–4 μm), compared to malate grown cells (6–7 μm). When R. benzoatilyticus JA2 cells were grown in malate bio-anodes, they presented higher potentials (289.22 ± 4.6 mV or 436.22 OCV per mg dry weight) compared to glucose bioanodes (163 ± 5.5 mv or 188.98 OCV per mg dry weight). Insights from the metabolomic footprints and fingerprints have revealed differential regulation of key components in the central metabolic pathway such as fumarate, citrate and succinate, which are significantly increased in malate grown bio anodes. Strain JA2 cells when grown with malate as substrate are densely grown on the electrodes and exhibited reduced size, when observed under SEM, which contrasts with control cells grown on malate broth. The artificial selection pressure of the MFC and the different metabolic pathways followed by these bacteria are the reasons for such discrepancy in the power production by the strain JA2. These adaptations may indicate survival advantage during the electron transfer and growth in bio anodes. The study throws light on what types of effluents would be more suitable as substrates for R. benzoatilyticus JA2 microbial fuel cells. Image 1 • Strain JA2 grown in 2 chambered MFC in varied carbon & electrogenicity is measured. • Carbon source is malate/glucose & JA2 has dissimilar electrogenic response. • Malate grown resting JA2 in the bio- anode produced high power compared to glucose. • When connected together malate JA2 acted as anode, glucose JA2 as cathode. • Dense colonization & different metabolome of the malate JA2 caused such discrepancy. [ABSTRACT FROM AUTHOR]

A phenol-degrading fungal strain Magnusiomyces capitatus QWD1 was isolated from activated sludge that was used to treat papermaking wastewater. Through parameters optimization, the optimal degradation conditions were found to encompass (NH 4) 2 SO 4 as nitrogen source (14 mmol/L), inoculum concentration of 15%, pH 7 and a temperature of 35 °C. Four different materials were used as carriers for the preparation of the microbial inoculum and the effect of storage temperatures on inoculum viability was investigated. With the prepared bioaugmentation inoculum addition to activated sludge, it was found to markedly increase the original system's treatment efficiency of phenol-containing wastewater. A high-throughput sequencing-based analyze approach revealed that the phenol-degrading inoculum addition can increase the abundance and diversity of fungi in the treatment system, which supports the development of a stable microbial ecosystem. The H 2 production of photosynthetic bacteria with the bioaugmented QWD1 inoculum was 32.4% higher than the control without inoculum addition when using the phenol-containing wastewater. • A phenol-degrading fungi was isolated from the sludge of papermaking wastewater. • The bioaugmentation enhanced the COD removal efficiency of phenolic wastewater. • The fungi addition could increase the hydrogen production yield for R. sphaeroides. [ABSTRACT FROM AUTHOR]

Abstract Hydrogen is a promising alternative to fossil fuel for a source of clean energy due to its high energy content. Some strains of phototrophic microorganisms are known as important object of scientific research and they are being explored to raise biohydrogen (BioH 2) yield. BioH 2 is still not commonly used in industrial area because of the low biomass yield and valuable down streaming process. This article deals with the methods of the hydrogen production with the help of two large groups of phototrophic microorganisms – microalgae and cyanobacteria. Microalgal hydrogen is environmentally friendly alternative to conventional fossil fuels. Algal biomass has been considered as an attractive raw source for hydrogen production. Genetic modified strains of cyanobacteria are used as a perspective object for obtaining hydrogen. The modern photobioreactors and outdoor air systems have been used to obtain the biomass used for hydrogen production. At present time a variety of immobilization matrices and methods are being examined for their suitability to make immobilized H 2 producers. Graphical abstract Image 1 Highlights • Hydrogen production from microalgae and cyanobacteria. • Mechanisms of biohydrogen metabolism. • Bioreactors for biohydrogen production process. • Enzymes of biohydrogen production. [ABSTRACT FROM AUTHOR]

Rhodobacter capsulatus is a photosynthetic bacterium with the ability to produce H 2 under photosynthetic condition. In this study, a new strain JL1 isolated from lake water was identified as Rhodobacter capsulatus by phylogenetic analysis of 16S ribosomal DNA (rDNA) sequence. Initial medium pH and l -glutamate (nitrogen source) concentration were optimized. At optimum pH 7.0 and 7 mmol/L l -glutamate, R. capsulatus JL1 could grow and produce hydrogen on the carbon sources of acetate, butyrate, glucose, xylose and fructose with the maximum substrate to H 2 conversion efficiencies of 67.5%, 26.6%, 46.1%, 46.2% and 46.6%, respectively. The maximum H 2 production rate, 124 ± 0.6 mL/(L·h), was obtained using 20 mmol-glucose/L as the carbon source. The addition of appropriate acetic acid to the tests with low concentration of glucose was able to improve the H 2 yield. Under the optimum operation parameters, the maximum H 2 yield and H 2 production rate of R. capsulatus JL1 from 16.4 g-corn straw/L-culture were 2966.5 ± 43.2 mL/L and 71.1 ± 4.5 mL/(L·h), while the chemical oxygen demand (COD) removal rate was up to 49.6%. This study indicates that R. capsulatus JL1 can serve as good candidate strain for H 2 production with organic waste water as well as effluent of dark-fermentation. [ABSTRACT FROM AUTHOR]

Two different process configurations SSP (simultaneous saccharification photo-fermentation) and SHP (separate hydrolysis photo-fermentation) for photo-fermentative hydrogen production using corn stover by mixed consortium of photosynthetic bacteria were compared. The effects of substrate concentration, initial pH and fermentative temperature on SSP and SHP were investigated. Cell growths and hydrogen production characteristics during the processes of SSP and SHP were also compared. The results showed that the optimal condition of SSP was substrate concentration of 30 g/L, initial pH of 5.5 and fermentative temperature of 40 °C, the corresponding hydrogen production was 83.87 mLH 2 /g corn stover, which was 27.8% higher than that of SHP. The cell growth time in SSP was longer than that in SHP, especially for extended exponential and stationary stages, which was helpful for hydrogen production. The highest cell concentration in SSP was 3.34 g/L, which was 36.3% higher than that of SHP. The peak hydrogen production rate in SSP increased linearly until 16.33 mL H 2 /h during 36–120 h, while the peak hydrogen production rate in SHP increased during 12–48 h and then decreased during 48–84 h, with a mean rate of 11.28 mL H 2 /h. [ABSTRACT FROM AUTHOR]

Hydrogen can be produced via dark and photo-fermentation using either single-stage or two-stage processes. The advantage of a two-stage system is that it is possible to separately optimize and control culture conditions for the dark and photo-fermentative bacteria. In the present study a mixture of starch and glucose was used as carbon source for the dark fermentation step. Response surface methodology (RSM) with a Box-Behnken design (BBD) was applied to the photo-fermentation stage for the optimization of key parameters: inoculum concentration ( Rhodopseudomonas palustris ), substrate concentration (dark fermentation effluent (DFE)) and pH. In this sequential two-stage system, the highest overall hydrogen yield (8.3 ± 0.1 mmol H 2 /gCOD), overall hydrogen production (1.62 mmol) and the photo fermentation yield (7.21 ± 0.2 mmol H 2 /gCOD) were achieved at inoculum of 9 mL (1.64 ± 0.7 × 10 8 cells), a DFE dilution of 2.5× and a pH of 7.5, which were center points of the design. 97% COD removal was achieved at the highest dilution of DFE (lowest concentration of carbon source) at pH 6.5. [ABSTRACT FROM AUTHOR]

It is increasing clear that biofuels can be a viable source of renewable energy in contrast to the finite nature, geopolitical instability, and deleterious global effects of fossil fuel energy. Collectively, biofuels include any energy-enriched chemicals generated directly through the biological processes or derived from the chemical conversion from biomass of prior living organisms. Predominantly, biofuels are produced from photosynthetic organisms such as photosynthetic bacteria, micro- and macro-algae and vascular land plants. The primary products of biofuel may be in a gas, liquid, or solid form. These products can be further converted by biochemical, physical, and thermochemical methods. Biofuels can be classified into two categories: primary and secondary biofuels. The primary biofuels are directly produced from burning woody or cellulosic plant material and dry animal waste. The secondary biofuels can be classified into three generations that are each indirectly generated from plant and animal material. The first generation of biofuels is ethanol derived from food crops rich in starch or biodiesel taken from waste animal fats such as cooking grease. The second generation is bioethanol derived from non-food cellulosic biomass and biodiesel taken from oil-rich plant seed such as soybean or jatropha. The third generation is the biofuels generated from cyanobacterial, microalgae and other microbes, which is the most promising approach to meet the global energy demands. In this review, we present the recent progresses including challenges and opportunities in microbial biofuels production as well as the potential applications of microalgae as a platform of biomass production. Future research endeavors in biofuel production should be placed on the search of novel biofuel production species, optimization and improvement of culture conditions, genetic engineering of biofuel-producing species, complete understanding of the biofuel production mechanisms, and effective techniques for mass cultivation of microorganisms. [ABSTRACT FROM AUTHOR]

Both dark and photo-fermentation can be used for biological hydrogen production; either performed separately, in two-stage systems, or in co-culture. A single stage process is less laborious and costly; however, the two types of microorganisms have different nutritional requirements requiring optimization of culture conditions. Here a response surface methodology (RSM) with a Box-Behnken design was used to optimize microorganism ratio and substrate and buffer concentrations, and to evaluate their interactive effects for maximization of hydrogen yield. Clostridium butyricum and Rhodopseudomonas palustris were grown on a potato starch/glucose base medium at 30 °C under continuous illumination (40 W m−2 light intensity). The highest hydrogen yield, 6.4 ± 1.3 mol H2/mol glucose, was obtained with a substrate concentration of 15 g/L, buffer concentration of 50 mM, and microorganism ratio of 3. The observed strong interaction between buffer and substrate concentration is most likely due to the need to optimize the pH for co-cultures. [ABSTRACT FROM AUTHOR]

Hydrogen is a promising alternative energy, and can be produced from various materials. Platanus orientalis leaves (POL) was utilized to produce hydrogen through simultaneous saccharification fermentative (SSF) method with photosynthetic bacteria HAU-M1. The method was investigated using response surface methodology (RSM) with central composite design (CCD). The Plackett–Burman design was first used to screen the factors (initial pH, light intensity, temperature, substrate concentration and initial inoculum) that influence SSF hydrogen production. Results indicated that initial pH, temperature and inoculation amount had a statistically significant effect on SSF hydrogen production. Central composite design was further carried out to evaluate interaction between the selected variables. The optimal conditions were determined to be initial pH of 6.18, temperature of 35.59 °C, and inoculation amount of 26.29% (v/v). The predicted maximum hydrogen yield was 65.03 mL H 2 /g TS, which was very close to the experimental result of 64.10 mL H 2 /g TS obtained under the optimal conditions. The R 2 value was 0.9396, indicating a good model fit for SSF hydrogen production. [ABSTRACT FROM AUTHOR]

A novel photothermal biomaterial, designated GeO 2 -SiO 2 -Chitosan-Medium-LaB 6 (GSCML), was prepared to improve photosynthetic bacteria (PSB) biofilm development and hydrogen production performance. This biomaterial employed spectral beam splitting technology to increase the overall utilization of the incident light spectrum, which LaB 6 nanoparticles (NPs) mainly absorb light at approximately 380–510 and 660–780 nm and convert it into heat energy; the transmit light is around 590 nm for PSB growth. The temperature increased, and the luminous intensity of the light transmitted through the prepared biomaterial are controlled by adjusting the LaB 6 NPs' content. The average biofilm growth rate and hydrogen production rate of the biofilm on the created biomaterial were 0.05 mg/cm 2 /day and 2.92 mmol/h/m 2 , which were 3.4 and 4.1 times higher than those of the glass slide, respectively. The properties of the GSCML biomaterial provide advantages for applications in immobilized cell technologies and photobioreactors. [ABSTRACT FROM AUTHOR]

Photofermentative hydrogen production from glucose was investigated using the mixed photoheterotrophic culture (NG07). High-throughput sequencing was applied to describe the characteristics of the diversity of the microbial community. Bioinformatic analysis of the sequencing result showed that photosynthetic bacteria were dominant in the microbial populations. Several key parameters were investigated by NG07 to assess biohydrogen production. Under optimal condition with 70 mM glucose, 5.0 mg/L Fe 2+ , and 35 °C temperature, a high hydrogen production rate (HPR) was 136.0 ± 5.6 mL/L/h, which is higher than previous reports. That was the first time the study had found the mixed microbial community could resist the high temperature of 45 °C for photohydrogen generation, and increasing glucose concentration would result in higher hydrogen yield. These results implied that the mixed photoheterotrophic culture had a high temperature tolerance and the possibility of bio-hydrogen production in high temperature region. [ABSTRACT FROM AUTHOR]

Photosynthetic bacteria can utilize organic matter from wastewater to produce hydrogen gas, and the application of this process is an environment-friendly approach to produce energy. However, photo-fermentative hydrogen production can be inhibited by ammonium, which exerts an inhibitory role on the expression and activity of nitrogenase, the pivotal enzyme in hydrogen production. In this study, we constructed mutant strains of Rhodopseudomonas palustris by manipulating of nitrogen-regulatory genes. Photo-fermentative hydrogen production assay showed the ammonium concentration that nifA draT2 and nifA glnK2 double mutant strains can tolerate increased by 25 and 10 folds, respectively, compared with wild-type strain, though hydrogen yield decreased with the increase of ammonium concentration. Results indicate that manipulation of nitrogen-regulatory genes is an effective way to enhance the ammonium tolerance of photosynthetic bacteria and improve their hydrogen production. [ABSTRACT FROM AUTHOR]

Huge amounts of rotten apples are generated in China, the biggest apple producer in the world. Bio-hydrogen production from apple waste is a promising strategy to treat this biomass waste, while producing hydrogen as renewable energy. In this study, apple waste was taken as a carbon source for bio-hydrogen production from high-efficient photosynthetic bacteria (PSB) HAU-M1. Effect of initial pH, light intensity, temperature and material to liquid ratio on the hydrogen production by HAU-M1 was evaluated using both single-factor design and response surface methodology (RSM). The optimal conditions were initial pH of 7.14, light intensity of 3029.67 lx, temperature of 30.46 °C, and material to liquid ratio of 0.21, respectively. A maximum specific hydrogen yield (SHY) of 111.85 ± 1 mL H 2 /g TS was obtained under the optimal conditions. In apple-production countries such as China, the success of hydrogen production from apple waste by PSB demonstrated a great application prospect on sustainable utilization of apple waste. [ABSTRACT FROM AUTHOR]

Microorganisms can produce hydrogen biologically, with species ranging from photosynthetic and fermentative bacteria to green microalgae and cyanobacteria. In comparison with the conventional chemical or physical hydrogen production methods, biological processes demonstrate several advantages by operating at ambient pressure and temperature conditions, without a requirement for the use of precious metals to catalyze the reactions. In addition to using cellular endogenous substrate from which to extract electrons for H 2 -production, a number of green microalgae are also endowed with the photosynthetic machinery needed to extract electrons from water, the potential energy of which is elevated by two photochemical reactions prior to reducing protons (H + ) for the generation of molecular hydrogen (H 2 ). Sunlight provides the energy for the microalgal overall strongly endergonic reaction of H 2 O-oxidation, electron-transport, and H 2 -production. Thanks to a substantial amount of research, a number of diverse experimental approaches have been developed and applied to establish and improve sustainable production of hydrogen. This review summarizes and updates recent developments in microalgal hydrogen production research with emphasis on new trends and novel ideas practiced in this field. [ABSTRACT FROM AUTHOR]

A newly isolated photosynthetic bacterium, Rhodobacter sphaeroides HY01 showed high hydrogen production performance and good flexibility on genetic modification. In order to investigate its potential on using wastewater containing heavy metal ions for photosynthetic hydrogen production, the effects of four conventional heavy metal ions, Pb 2+ , Cu 2+ , Cr 6+ and Cd 2+ , on the photosynthetic hydrogen production performance of R. sphaeroides HY01 were studied. The results suggested that the concentration of Pb 2+ 0.5 mg/L, Cu 2+ 0.05 mg/L, Cr 6+ 0.05 mg/L, Cd 2+ 20 mg/L showed maximum positive effects on the hydrogen production rates and yields. This strain cultured in different heavy metal ions at optimum concentrations showed similar growth curves and optical density. The removal efficiency of heavy metal ions were determined to be 65%–76% for Cd 2+ , 54%–80% for Cr 6+ , 30%–38% for Pb 2+ and 96%–100% for Cu 2+ . The results suggest that HY01 was sensitive to Cr 6+ and Pb 2+ , and relative of high tolerance to Cu 2+ and Cd 2+ . [ABSTRACT FROM AUTHOR]

Photofermentation and lipid accumulation by the purple non-sulfur photosynthetic bacterium, Rhodobacter sp. KKU-PS1, from malic acid was investigated in batch fermentation. Media compositions including malic acid concentration, glutamate concentration, amount of vitamin addition and Fe concentration were optimized by response surface methodology with central composite design in order to achieve a maximum hydrogen production rate (R m ). The predicted R m of 11.7 mL H 2 /L. h was obtained under optimal media compositions of 2.36 g/L malic acid, 224 mg/L glutamate, and 13.5 mL/L of vitamin solution addition along with 64 mg/L of Fe. The cellular lipid content in Rhodobacter sp. KKU-PS1 was checked at the end of photo-fermentative process. A nitrogen limited condition was suitable for lipid accumulation by Rhodobacter sp. KKU-PS1. A maximum lipid production of approximately 592 mg/L was obtained with 4.7 g/L malic acid, 159 mg/L glutamate, 21.7 mL/L of vitamin solution along with 330 mg/L Fe (equivalent to C/N ratio of 132). Triacylglycerol (TAG) was the major component of the lipid in which the predominant fatty acid was octadecanoic acid (C18:1) in the form of oleic acid (C18:1n-9). The physicochemical properties of biodiesel predicted from fatty acid methyl esters (FAMEs) compositions of lipid produced by Rhodobacter sp. KKU-PS1 under the suitable conditions indicated that the lipid produced by the strain KKU-PS1 has a fairly good potential for use as biodiesel. [ABSTRACT FROM AUTHOR]

A marine photosynthetic bacterial strain LC83 was isolated from bathing beach sludge and identified as Marichromatium purpuratum using light microscopic examination, Biolog tests, and 16S rRNA gene sequence analysis. The strain is a salt- and alkali-tolerant, vitamin-independent facultative anaerobe with an optimum sodium chloride (NaCl) concentration of 30‰, initial optimum pH of 7.0–8.0, optimum temperature of 30 °C, and optimum light intensity of 80–160 μmol/m 2 /s. The addition of M. purpuratum LC83 to the dark fermentation of Pantoea agglomerans BH-18 for 8 h clearly improved the pH and the oxidation–reduction potential of the fermentative liquid, retarded the reduction in glucose, and maintained the balance between the glucose generated photosynthetically by the photosynthetic bacteria and those consumed by the fermentative bacteria in the early stage of coupled fermentation. The addition of photosynthetic bacteria to dark fermentation at 8 h improved the fermentative liquid conditions in favor of hydrogen production. The yield of hydrogen and the amount of glucose consumed by the coupled fermentation were also both higher than during pure fermentation by P. agglomerans BH-18. The optimum inoculation ratio was 1/8 (strains BH-18/LC83). The coupled dark and photofermentation of M. purpuratum LC83 and P. agglomerans BH-18 is a feasible way of improving the level of hydrogen produced in marine culture. [ABSTRACT FROM AUTHOR]

The photosynthetic bacteria have a very versatile metabolic repertoire and have been known for decades to produce hydrogen during photofermentative growth. Here, recent advances in hydrogen production by these organisms are reviewed and future directions highlighted. Often used as a second stage in two stage hydrogen production processes; first stage fermentative sugar to hydrogen and organic acids; second stage, organic acids to hydrogen, recent studies have highlighted their ability to directly convert sugars to hydrogen. Several studies have attempted to optimize a single stage batch process and these, and a study with continuous cultures have shown that yields approaching 9 mol H 2 /mol glucose can be obtained. One of the drawbacks of this system is the dependency on light, necessitating the use of photobioreactors, thus potentially greatly adding to the cost of such a system. In another approach which avoids the use of light energy, microaerobic fermentation of organic acids to hydrogen, driven by limited oxidative phosphorylation has been demonstrated in principle. Further advances will probably require the use of metabolic engineering and more sophisticated process controls in order to achieve higher stoichiometries, approaches that might be applied to other, light dependent, hydrogen production process by these organisms. [ABSTRACT FROM AUTHOR]

Phenol biodegradation is usually limited by a low treatment efficiency due to the microbial inhibition with intermediate accumulation. In this study, we report a two-step process to efficiently convert phenol to H 2 . In the first step, phenol was converted to benzoate by mixed anaerobic cultures in an acidogenic reactor; subsequently, the formed benzoate was further fermented to H 2 by Rhodopseudomonas palustris , an efficient photosynthetic bacterium. The individual steps were simulated by mathematical models. The modified Gompertz model was used to describe the H 2 production process from benzoate by R. palustris . The results show that the effluent from the acidogenic reactor treating phenol could be directly used by R. palustris for H 2 production. The maximum H 2 production rate was estimated to be 0.545 mL/h. The H 2 yield and light conversion efficiency were 0.58 and 2.08%, respectively. The results of this study suggest that such a two-step process can efficiently degrade aromatic compounds like phenol with concurrent H 2 production. [ABSTRACT FROM AUTHOR]

Single-stage hydrogen production from glucose was investigated using the marine photosynthetic bacterium Rhodovulum sulfidophilum TH-79, a Tn7 transposon mutant of strain P5. The mutation in strain TH-79 did not affect its cell growth in glucose medium compared with the parent strain. TH-79 displayed improved photoheterotrophic hydrogen production performance when the medium contained glucose or galactose as the sole carbon source. The mutant produced about 7.07 mol H 2 /mol glucose, which is similar to the yields of more complicated integration systems. A one-stage photofermentation system using a seawater culture medium appears to be a promising alternative to the integration of dark- and photofermentation systems. [ABSTRACT FROM AUTHOR]

Thirty-nine purple non-sulfur bacteria (PNSB) were isolated from 162 environmental samples. These isolates of PNSB were tested for their ability to produce biohydrogen (Bio-H 2 ) at 40 °C and only 14 isolates were noted to possess such ability, which were considered as thermotolerant photosynthetic Bio-H 2 producing bacteria (tt-PHPB). Of 14 isolates of tt-PHPB, KKU-SN1/1 was observed to have the highest Bio-H 2 productivity. Central composite design was employed to optimize the operating conditions for maximal Bio-H 2 production by the strain KKU-SN1/1. Under optimal conditions (7.6 g/L malic acid, 11 g/L glutamic acid, pH 6.7, at 40 °C) the Bio-H 2 production was increased by 68.28%. The purity of Bio-H 2 produced was 92.22%, as suggested by gas chromatography (GC-TCD). Based on morphological characteristics and 16S rDNA sequence analysis, the strain KKU-SN1/1 was identified as Rhodopseudomonas pentothenatexigens , with 99.7% similarity. To our knowledge, this is the first report on Bio-H 2 production by R . pentothenatexigens KKU-SN1/1. [ABSTRACT FROM AUTHOR]

Abstract: A purple non-sulfur (PNS) photosynthetic bacterium was isolated from an upflow anaerobic sludge blanket (UASB) bioreactor for methane production and was identified as Rhodobacter sphaeroides KKU-PS5 (GenBank Accession no. KC481702) by 16s rRNA gene sequence analysis. Strain KKU-PS5 could utilize glucose, xylose, fructose, arabinose, malate, succinate, acetate, butyrate, lactate and D-mannitol for growth and hydrogen production. Malate was a preferred carbon source while glutamate and Aji-L (waste from the process of crystallizing monosodium glutamate) were the preferred nitrogen sources. The ability to utilize Aji-L as a low-cost nitrogen supplement for photo-biohydrogen production by the strain KKU-PS5 is considered as its desirable characteristic. The threshold substrate concentration of malate was 30 mmol/L. The optimum conditions for hydrogen production from malate were an initial pH of 7.0, FeSO4 concentration of 4 mg/L, temperature of 30 °C and light intensity of 6 klux. Under the optimum conditions, the maximum hydrogen production, the hydrogen yield (HY) and the hydrogen production rate (HPR) of 1330 mL-H2/L, 3.80 mol-H2/mol-malate, and 11.08 mL-H2/L h, respectively, were achieved. Hydrogen production under a dark/light cycle led to a decreased HY and HPR in comparison to continuous illumination. [Copyright &y& Elsevier]

Abstract: Rhodobacter sphaeroides 2.4.1 is a facultative photosynthetic purple nonsulfur bacterium that can generate hydrogen by using sunlight and organic carbon sources under anaerobic conditions. Hydrogen is produced by the nitrogenase. To optimize hydrogen production, we combined in a single strain several mutations known to enhance hydrogen production in anoxygenic phototrophic bacteria. The first metabolic engineering approach involved elimination of the major reductive pathways (electron sinks) that compete for electrons with the nitrogenase. A strain containing mutations in the pathways involving hydrogen uptake hydrogenase (hupSL), poly-β-hydroxybutyrate synthesis (phbC), and light harvesting complex-II (pucBA) showed significantly increased hydrogen production. The second approach involved increasing immediate electron flow to nitrogenase via the Rnf complex. This strategy resulted in modest improvements in hydrogen yield. The third approach involved upregulating nitrogenase expression and decoupling its expression from the presence of ammonium in the growth media. Mutations in the nifA gene, encoding the master transcriptional activator of nitrogen fixation genes, were found to be most effective for increasing total hydrogen yield, accelerating hydrogen production, and making this process tolerant to the presence of ammonia in the medium. The combination of beneficial mutations resulted in an additive and superior hydrogen producing strain of R. sphaeroides. [Copyright &y& Elsevier]

Abstract: H2 is a clean, renewable and energy-efficient fuel. However, in order for it to be a fuel effectively utilizable at an industrial level, key issues about its economically and environmentally sustainable production have still to be solved. Microbial hydrogen production is a process with a low environmental impact and, among microbial processes, photofermentation is considered a promising and sustainable solution. However, the energy input for the biological processes is still higher than the energy output in the form of H2 gas. One possibility for improving this ratio is to increase the efficiency of the process while at the same time reducing electricity consumption, both of which relate to the issue of an optimal photobioreactor design. This review focuses on recent advances made in photobioreactor design towards higher light conversion efficiency, a greater hydrogen production rate and substrate conversion in hydrogen production processes carried out with purple non sulfur bacteria, giving particular attention to the light source and to illumination protocols. Recent achievements in outdoor hydrogen production in large scale photobioreactors are also reviewed. [Copyright &y& Elsevier]

Abstract: To enhance bacterial adhesion and biofilm activity, a new support material named as SiO2-Chitosan-Medium Sol is proposed for hydrogen production by photosynthetic bacteria. The physicochemical properties of the support material are comparatively investigated with other four different materials in terms of topography, surface energy and composition. And the biocompatibilities to Rhodoseudomonas palustris CQK 01 for these five support materials are experimentally studied by quantifying the initially adhered cell numbers, biofilm dry-weights, protein and polysaccharide in EPS of the biofilms and the average H2 production rates. Experimental results show that the proposed support material shows favorable properties like rough surface, amine group and nutrients. The new support material enhances the cell adhesion capacity, reduces the biofilm formation time and improves the biofilm activity. The average H2 production rate of the bioreactor with proposed support material was improved by 80% compared with the rate of the bioreactor with the unmodified material. [Copyright &y& Elsevier]

Abstract: A differential-discrete mathematical model is developed to predict the photosynthetic bacteria (PSB) Rhodopseudomonas palustris CQK 01 biofilm formation. In this model, with the consideration of the light decay in the photobioreactor, PSB inactivation and cellular automata (CA) rules along with the previously obtained growth kinetics parameters of PSB are used to simulate biofilm growth. With this model, the effects of illumination intensity, pH value and initial inoculation on the biofilm morphology, active cell biomass as well as some characteristic parameters such as porosity, roughness and thickness is investigated. Numerical results show that cell inactivation occurs within the biofilm and the biofilm morphology varies with the operating conditions. Moreover, the roughness and thickness increase, but the porosity decreases as the biofilm grows. The amount of active cells is increasing with time. It is also found that the optimal conditions for PSB biofilm formation are the illumination intensity of 6000 lx, the initial inoculation of 60 and the substrate solution pH value of 7.0. [Copyright &y& Elsevier]

To obtain additional hydrogen recovery from the downstream photosynthetic biohydrogen reactor (PBR), a system (PBR1–MFCs–PBR2) that combined PBRs with three single chamber microbial fuel cells (MFCs) was proposed in this study. The results revealed that the PBR2 in PBR1–MFCs–PBR2 showed a hydrogen production rate of 0.44 ± 0.22 mmol L h−1, which was 15 and 4 times higher than those obtained by direct connecting the two PBRs (PBR1–PBR2) and pH regulated system (PBR1–pH regulation–PBR2), respectively. In addition, the PBR1–MFCs–PBR2 exhibited the highest glucose utilization (η g) of 97.6 ± 2.1 %, while lower η g values of 75.6 ± 2.2% and 70.1 ± 1.2% was obtained for PBR1–PBR2 and PBR1–pH regulation–PBR2, respectively. These improvements were due to the removal of inhibitory byproduct and H+ from the PBR1 effluent by the MFCs. [ABSTRACT FROM AUTHOR]

Abstract: In this study, hydrogen production by Rhodobacter sphaeroides RV from acetate was investigated. Ammonium sulphate and sodium glutamate were used to study the effects of nitrogen sources on photosynthetic hydrogen production. The results showed the optimal concentrations for ammonium sulphate and sodium glutamate were in the range of 0.4–0.8 g/L. Orthogonal array design was applied to optimize the hydrogen-producing conditions of the concentrations of yeast, FeSO4 and NiCl2. The theoretical optimal condition for hydrogen production was as follow: yeast 0.1 g/L, FeSO4 100 mg/L and NiCl2 20 mg/L. [Copyright &y& Elsevier]

Abstract: Rhodobacter capsulatus (R. capsulatus), which is a typical purple nonsulfur photosynthetic bacterium, is able to produce hydrogen under photosynthetic condition. A mutant of R. capsulatus named MC122 was obtained by Tn5 transposon mutagenesis. The transposon mutant had improved photoheterotrophic hydrogen production performance using acetic acid as substrate and its mutation site was located by sequencing the rescued plasmid containing the transposon insertion from the genome of the mutant. It was found for the first time that disruption of the multidrug resistance protein (mdtB) gene resulted in improved hydrogen production. [Copyright &y& Elsevier]

Abstract: One of the major limiting factors in the practical implementation of Microbial Fuel Cells is finding efficient and sustainable catalysts for the cathode half reaction, in an attempt to avoid expensive and/or toxic catalysts. The use of phototrophic organisms is one good option since they can act as efficient in-situ oxygenators thus facilitating the cathodic reaction. In the present study, the oxygen production by photosynthetic organisms was shown to be light dependant, which resulted in increasing the power generation by 42%. Furthermore, this study showed that a previously abiotic cathode that turned biotic showed a clear light response with an improved performance of 48%. Oxygen depletion in a water-based cathode can be avoided with the use of photosynthetic biocatalysts, thus providing sustainable operation for MFCs. [Copyright &y& Elsevier]

Abstract: [FeFe]-Hydrogenases, encoded by hydA are thought to require the products of three accessory genes, hydE, F and G, for the biosynthesis of a functional H-cluster and maturation into a functional protein capable of reducing protons to hydrogen. Genome sequencing has shown that some organisms, including several strains of purple non-sulfur photosynthetic bacteria, possess orphan hydAs. It is unknown if these orphan HydAs can be matured into functional proteins. A construct where transcription of the apparent orphan hydA of Rhodospirillum rubrum was driven by the nifH2 promoter failed to restore hydrogen production to a Nif− strain of R. rubrum under nitrogen-limited photoheterotrophic conditions. However, RrhydA could be overexpressed and matured in Escherichia coli BL21(DE3) containing the hydE, F and G maturation genes from Desulfovibrio vulgaris Hildenborough or Clostridium acetobutylicum ATCC 824. Co-expression of R. rubrum hydA with the maturation genes of C. acetobutylicum gave the highest hydrogenase activity, 107 nmol/min/mg, whereas it was 6.6 nmol/min/mg with the maturation genes from D. vulgaris. Interestingly, R. rubrum HydA was twice as active as the HydA of C. acetobutylicum when both were matured with the maturases from the latter organism. [Copyright &y& Elsevier]

Abstract: Hydrogen (H2) is a promising alternative energy carrier which can be produced biologically. Rhodobacter capsulatus, a non-sulfur purple photosynthetic bacterium, can produce H2 under nitrogen-limited, photoheterotrophic conditions by using reduced carbon sources such as simple organic acids. Outdoor closed photobioreactors; used for biological H2 production are located under direct sunlight, as a result; bioreactors are exposed to temperature fluctuations during day time. In this study to overcome this problem, temperature-resistant mutants (up to 42°C) of R. capsulatus were generated in this study by a directed evolution approach. Eleven mutant strains of R. capsulatus DSM 1710 were obtained by initial ethyl methane sulfonate (EMS) mutagenesis of the wild-type strain, followed by batch selection at gradually increasing temperatures up to 42°C under respiratory conditions. The genetic stability of the mutants was tested and eight were genetically stable. Moreover, H2 production of mutant strains was analyzed; five mutants produced higher amounts of H2 when compared to the DSM 1710 wild-type strain and three mutants produced less H2 by volume. The highest H2- producing mutant (B41) produced 24% more H2 compared to wild type, and the mutant with lowest H2-production capacity (A52) generated 7% less H2 compared to the wild type. These results indicated that heat resistance of R. capsulatus can be improved by directed evolution, which is a useful tool to improve industrially important microbial properties. To understand molecular changes that confer high temperature-resistance and high hydrogen production capacity to these mutants, detailed transcriptomic and proteomic analyses would be necessary. [Copyright &y& Elsevier]

Abstract: A two-dimensional model is developed to describe the photosynthetic bacteria (PSB) biofilm formation on the solid surface in a flat-panel photobioreactor. The diffusion-reaction equations and cellular automata (CA) rule along with the previously obtained growth kinetics parameters of PSB are used to simulate the coupled mass transport and biochemical reaction as well as the biomass growth. With this model, the effects of the illumination intensity, pH value and initial inoculation on the formed biofilm morphology, porosity, roughness and thickness are investigated. Numerical results show that the biofilm porosity and thickness continuously decreases and increases during the PSB biofilm formation process, respectively, while the surface roughness reaches a stable value after a certain time. The optimal conditions for the PSB biofilm formation are the initial inoculation of 500, and the illumination intensity of 5000 lx and pH value of 7.0. [Copyright &y& Elsevier]

Abstract: An ultrasonic treatment technique was applied to a continuous photobioreactor with Rhodopseudomonas palustris CQK 01 suspension to enhance photo-hydrogen production performance. After the start-up period, R. palustris CQK 01 suspension in the photobioreactor was intermittently agitated by ultrasonic wave with a frequency of 20 kHz and then the hydrogen production performance was evaluated. The ultrasonic agitation significantly dropped the hydrogen concentration in the suspension from 300 μmol/L to 50 μmol/L and thus increased the hydrogen production rate and hydrogen yield by nearly 2 times as compared with conventional photobioreactor. Furthermore, the effects of the ultrasonic power and time, influent substrate flow rate and concentration were investigated and discussed, respectively. The maximum hydrogen production performance of the continuous photobioreactor with ultrasonic treatment was obtained under the conditions of ultrasonic power 40 W, agitation/interval time 3/7 s, substrate concentration 75 mmol/L and substrate flow rate 40 ml/h, leading to the hydrogen production rate of 1.12 mmol/L/h and hydrogen yield of 0.23 mol-H2/mol-glucose. [Copyright &y& Elsevier]

Abstract: For improving photo-biohydrogen production, a novel gas bubble column photobioreactor with Ar gas sparging was developed for biohydrogen production by purple non-sulfur phototrophic bacteria, Rhodoseudomonas palustris CQK-01. The dissolved hydrogen concentration was in-situ measured by a hydrogen microsensor. Experimental results demonstrated that Ar gas sparging dramatically decreased the dissolved hydrogen concentration, resulting in an improvement in the photo-biohydrogen production performance. Furthermore, effects of the gas flow rate and the time interval of gas sparging were investigated. The results showed that with an increase in the gas flow rate, the hydrogen production performance increased initially due to the reduced dissolved hydrogen concentration and enhanced mass transport, and then it decreased as a result of an increased shear stress. Meanwhile, the short sparging time interval resulted in a low accumulation of dissolved hydrogen in the bioreactor, hence high hydrogen production performance. The optimal hydrogen production rate (5.86 mmol/l/h) and hydrogen yield (3.38 mol H2/mol glucose) were obtained at the gas flow rate of 10 ml/min, respectively. [Copyright &y& Elsevier]

Abstract: A marine photosynthetic bacterial consortium was studied for its capability of hydrogen production using treated soy sauce wastewater and bagasse as a sole carbon source. Denaturing gradient gel electrophoresis (DGGE) profiles showed that the dominant bacterium in the bacterial consortium was Rhodobium marinum. The effects of treatments of soy sauce wastewater were tested for hydrogen production. The feedstock treatments included dilution, sterilization, neutralization and by adding sodium bicarbonate and yeast extract. The maximal cumulative hydrogen production was achieved up to 200 ± 67 mL H2 in the medium containing soy sauce and 41 ± 16 mL H2 from the hydrolyzed bagasse as substrate. [Copyright &y& Elsevier]

Abstract: A new hydrogen-producing photosynthetic bacterium, designated as Rhodovulum sulfidophilum P5, was enriched and isolated from the sludge of a marine shrimp cultivation farm. During fermentation, hydrogen was mainly produced in the late exponential and stationary phases. The optimum culture conditions of strain P5 for hydrogen production were NaCl concentration of 20 g/L, initial pH of 8, temperature of 30 °C, and light intensity of 100 μmol photons/m2 s. The maximum hydrogen yield and rate were 2.56 ± 0.18 mol/mol acetate and 19.4 ± 1.6 mL/L h, respectively. Under optimum culture conditions, the hydrogen conversion efficiencies of P5 from acetate, propionate, and butyrate were (64.62 ± 5.05)%, (17.95 ± 0.72)%, and (41.83 ± 2.68)%, respectively. Taken together, these results suggest that this strain has a high salt tolerance and the potential to be used for biohydrogen production and biological treatment of marine organic wastewater. [Copyright &y& Elsevier]