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N2-fixing cyanobacteria are highly promising microorganisms for sustained and improved H2 production. Among various N2-fixing cyanobacteria that have ability to produce H2, Fischerella muscicola TISTR 8215 is a promising strain with high potential for H2 production. The production of H2 by the two microorganisms, i.e., cyanobacteria and microalgae was investigated to improve photobiological H2 production. The results showed that co-culturing the green microalga Chlorella sp. (initial biomass concentration = 0.025 g L−1, 5% algal culture) with dominant cyanobacterium F. muscicola TISTR 8215 (initial biomass concentration = 0.5 g L−1, 95% cyanobacterial culture) increased total accumulated H2 yield about 1.5-fold compared to the monoculture of F. muscicola TISTR 8215. However, the decrease of accumulated H2 yield was observed when increasing initial cell concentration of Chlorella sp. to initial biomass concentration = 0.125 g L−1 in co-cultivation system. Notably, the co-immobilization of F. muscicola TISTR 8215/Chlorella sp. in 0.8% (w/v) agar led to a 11-fold increase in maximum H2 yield of 13.2 mmol H2 L−1 compared to the co-culture with no immobilization. In addition, the co-immobilization of F. muscicola TISTR 8215 and Chlorella sp. in agar cubes was able to prolong biohydrogen production for 3 cycles up to 324 h. The overall results demonstrated the improvement of H2 production by co-cultivation of F. muscicola TISTR 8215 and Chlorella sp. under optimized conditions. [ABSTRACT FROM AUTHOR]

To develop H2 photoproduction by using the N2-fixing cyanobacterium Fischerella muscicola TISTR 8215, a novel strain isolated from soil in Thailand, the factors affecting H2 production were investigated in this study. Enhanced H2 production in suspension culture was obtained when adapting the cells under N2-fixing condition (modified AA medium) with continuous illumination of 250 μmol photons m−2 s−1 under aerobic condition for 24 h, followed by further incubation under anaerobic condition for 9 h for production phase. The maximum H2 production rate was 38.5 μmol mg−1 chl a h−1. Low concentration of Fe2+ and Mo6+, essential elements for nitrogenase, enhanced H2 production. The enhanced H2 production was accompanied by the upregulation of nifD. On the other hand, an increased hupL transcript level was observed when there was a decrease of H2 production. In cells immobilization, 1.5% (w/v) agar-immobilized cells had a 23-fold increase in maximum H2 yield compared with that using free cell suspension at the same cell concentration, i.e., 7.48 mmol H2 L−1 by immobilized cells and 0.32 mmol H2 L−1 by suspended cells. Moreover, cell immobilization in agar could prolong H2 production up to 108 h. This study underlines the strategies toward enhanced and sustained H2 production from cyanobacteria. Furthermore, it will pave the way for large-scale production of biohydrogen to be used as an eco-friendly energy resource. [ABSTRACT FROM AUTHOR]