Hydrogen photoproduction by filamentous non-heterocystous cyanobacterium Plectonema boryanum and simultaneous release of ammonia

Abstract

Plectonema boryanum (filamentous, non-heterocystous cyanobacterium) photoproduced H2 when cells grown aerobically in nitrate were transferred to microaerobic or anaerobic conditions without nitrate. It was observed that H2 photoproducing cells simultaneously excreted ammonium in the medium, which was possibly due to phycocyanin degradation [decrease in chlorophyll a (Chl a):phycocyanin ratio in comparison to aerobic nitrate-grown cells]. Although nitrogenase (measured as H2 evolution) was induced in Ar:CO2 (96:4 v/v), inclusion of N2 in the gas phase (Ar:CO2:N2, 72:4:24 v/v) resulted in a 2-fold increase in H2 evolution. Addition of l-methionine DL-sulphoximine (MSX, glutamine-synthetase inhibitor), besides stimulating ammonium excretion in the medium, resulted in a 4.5-fold increment of H2 photoproduction (1.43 μmol H2 mg-1 dry wt h-1) in comparison to cells in Ar:CO2 gas phase (0.31 μmol H2 mg-1 dry wt h-1). Inhibition of photosystem II by 3(3,4-dichlorophenyl)1,1-dimethyl urea (DCMU) caused an increment of 1.6 and 3.2-fold in Ar:CO2 and Ar:CO2:N2, respectively, in comparison to cells incubated in Ar:CO2 gas phase alone. Simultaneous production of H2 and NH4+ was at a maximum when MSX and DCMU were added together in suboptical concentrations. Immobilization of cells in calcium alginate prolonged the duration (12 days) of H2 evolution and NH4- excretion. © 1992.