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Culture pH is very crucial to hydrogen production in the photo-fermentation process. Excessively low pH can directly affect cell growth and hydrogen production by changing bacterial physiological characteristics. Thus, screening acid-tolerant strains that can alleviate acid stress with enhanced hydrogen production is essential. In this work, an acid-tolerant mutant Rhodobacter capsulatus AT11 was isolated by transposon technology, and its photosynthetic characteristic under different initial pH values was investigated. The results indicated that the H2 yield of AT11 at initial pH of 5.5 was 4682.64 mL·L−1, which was 310.65% higher than that of wild strain JL1, and the mutant gene in AT11 was electron transfer flavoprotein (etf). Then an etf-deletion mutant JL1401 was constructed by deleting etf to verify the effect of etf on H2 production and investigate the acid-tolerance mechanism. Its H2 production at initial pH of 5.5 was significantly increased compared to its parental strain JL1. In addition, its photosynthetic characteristic with ammonium additives was studied. Under the condition of 1.8 mM ammonium, hydrogen production was still up to 2637.14 ± 41.46 mL·L−1, while hydrogen production of JL1 was inhibited. Cornstalk hydrolysate was used to evaluate the practical application of the constructed acid-tolerant mutant strains. The hydrogen yield reached 249.3 ± 16.8 mL-H2·g−1-cornstalk and 285.3 ± 19.1 mL-H2·g−1-cornstalk by R. capsulatus AT11 and JL1401, which were 2.9-fold and 3.3-fold compared to that of WT strain JL1, respectively. [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]

The effects of hydrolysis methods (hydrothermal, acid, alkali, hydrothermal-enzyme, acid-enzyme, and alkali-enzyme) on hydrolysate characteristics and photo fermentative hydrogen production (PFHP) of corn straw (CS) and sorghum straw (SS) were investigated. The optimum production of reducing the sugar of straw in different solvent environments was studied by one-step hydrolysis and co-enzymatic hydrolysis pretreatment through a 3,5-dinitrosalicylic acid method. The hydrogen production process by photolytic fermentation of hydrolysates of Rhodobacter sphaeroides HY01 was further analyzed through a gas chromatograph, including the differences in accumulated PFHP yield, chemical oxygen consumption (COD), and volatile fatty acid (VFA) composition. The results showed that the highest reducing sugar yield was obtained by the acid method among one-step hydrolysis. In contrast, acid-enzyme hydrolysis can further increase the reducing sugar yield, which reached 0.42 g·g−1-straw of both straws. Both CS and SS had the highest hydrogen yield from acid-enzyme hydrolysate, 122.72 ± 3.34 mL·g−1-total solid of straw (TS) and 170.04 ± 4.12 mL·g−1-TS, respectively, compared with their acid hydrolysates with 40.46% and 10.53% higher hydrogen yields, respectively. The use of enzymatic hydrolysis showed a significantly higher hydrogen yield for CS compared to SS, indicating that acid hydrolysis was more suitable for SS and acid-enzyme hydrolysis was more suitable for CS. [ABSTRACT FROM AUTHOR]

Furfural, as a typical byproduct produced during the hydrolysis of lignocellulose biomass, is harmful to the photo fermentation hydrogen production. In this work, the effects of furfural on the photo fermentation hydrogen production by Rhodobacter capsulatus using glucose as substrate were investigated. The characteristics of cell growth, hydrogen production, and fermentation end-products with the addition of different concentrations of furfural (0–20 mM) were studied. The results showed that furfural negatively affected the maximum hydrogen production rate and total hydrogen yield. The maximum hydrogen yield of 2.59 ± 0.13 mol-H2/mol-glucose was obtained without furfural. However, 5 mM furfural showed a 40% increase in cell concentration. Furfural in high concentrations can favor the overproduction and accumulation of inhibitive end-products. Further analysis of energy conversion efficiency showed that most of the energy in the substrate was underused and unconverted when the furfural concentration was high. The maximum glucose consumption (93%) was achieved without furfural, while it dramatically declined to 7% with 20 mM furfural addition. The index of half-maximal inhibitory concentration was calculated as 13.40 mM. Moreover, the possible metabolic pathway of furfural and glucose was discussed. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel 70 L tubular photo-bioreactor for biohydrogen production was constructed. • The LCE of 4% can be achieved by the method of the built-in light source. • Maximum hydrogen yield of 7 mol H 2 /mol glucose was obtained in the batch stage. • The average hydrogen production rate can reach 22.8 mL H 2 /(L·h) at HRT of 5 d. A novel 70 L composite tubular photo-bioreactor was constructed, and its photo-fermentation hydrogen production characteristics of batch and continuous modes were investigated with glucose as the substrate in an outdoor environment. In the batch fermentation stage, the hydrogen production rate peaked at 37.6 mL H 2 /(L·h) accompanied by a high hydrogen yield of 7 mol H 2 /mol glucose. The daytime light conversion efficiency is 4 %, with 37 % of light energy from the sun. An optimal hydraulic retention time of 5 d was identified during continuous photo-fermentation. Under this condition, the stability of the cell concentration is maintained and more electrons can be driven to the hydrogen generation pathway while attaining a hydrogen production rate of 20.7 ± 0.9 mL H 2 /(L·h). The changes of biomass, volatile fatty acids concentration and ion concentration during fermentation were analyzed. Continuous hydrogen production by composite tubular photo-bioreactor offers new ideas for the large-scale deployment of photobiological hydrogen production. [ABSTRACT FROM AUTHOR]