Enhanced H2 production with efficient N2-fixation by fructose mixotrophically grown Anabaena sp. PCC 7120 strain disrupted in uptake hydrogenase

Abstract

To explore the potential of a model filamentous cyanobacterium Anabaena sp. PCC 7120 for solar based biohydrogen production, an inactivated uptake hydrogenase ΔHupL strain was used in combination with fructose induced N2-fixing ability of the cells. The results revealed that fructose supports N2-fixing and H2-metabolism in ΔHupL strain. Cells showed an increase in growth rate, pigment content, and the formation of mature heterocysts within 6 h after growing under light-fructose mixotrophic condition. Upon supplementation of optimum fructose concentration at 60 mM, the cells grown for 24 h showed a 3.1-fold increase of nitrogenase activity in conjunction with an increase of nifD expression, with increased electron flow from utilization of fructose through the oxidative pentose phosphate pathway. Nitrogenase rather than bidirectional hydrogenase was likely responsible for the fructose mediated increase of H2-production. The maximum H2-production rate of ΔHupL strain under fructose mixotrophic growth was 101.33 μmolH2 mg chl a−1 h−1, accounting for a 4.7-fold increase compared to wild type under the same condition. Overall results indicated that fructose supplementation enabled Anabaena sp. PCC 7120 strain ΔHupL to increase N2-fixation leading to an enhanced H2-production.