Improvement of photobiological hydrogen production by suspended and immobilized cells of the N2-fixing cyanobacterium Fischerella muscicola TISTR 8215

To develop H-2 photoproduction by using the N-2-fixing cyanobacterium Fischerella muscicola TISTR 8215, a novel strain isolated from soil in Thailand, the factors affecting H-2 production were investigated in this study. Enhanced H-2 production in suspension culture was obtained when adapting the cells under N-2-fixing condition (modified AA medium) with continuous illumination of 250 mu mol 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 H-2 production rate was 38.5 mu mol mg(-1) chl a h(-1). Low concentration of Fe2+ and Mo6+, essential elements for nitrogenase, enhanced H-2 production. The enhanced H-2 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 H-2 production. In cells immobilization, 1.5% (w/v) agar-immobilized cells had a 23-fold increase in maximum H-2 yield compared with that using free cell suspension at the same cell concentration, i.e., 7.48 mmol H-2 L-1 by immobilized cells and 0.32 mmol H-2 L-1 by suspended cells. Moreover, cell immobilization in agar could prolong H-2 production up to 108 h. This study underlines the strategies toward enhanced and sustained H-2 production from cyanobacteria. Furthermore, it will pave the way for large-scale production of biohydrogen to be used as an eco-friendly energy resource.