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

Abstract

Abstract Plectonema boryanum (filamentous, non-heterocystous cyanobacterium) photoproduced H 2 when cells grown aerobically in nitrate were transferred to microaerobic or anaerobic conditions without nitrate. It was observed that H 2 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 H 2 evolution) was induced in Ar:CO 2 (96:4 v/v), inclusion of N 2 in the gas phase (Ar:CO 2 :N 2 , 72:4:24 v/v) resulted in a 2-fold increase in H 2 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 H 2 photoproduction (1.43 μmol H 2 mg −1 dry wt h −1 ) in comparison to cells in Ar:CO 2 gas phase (0.31 μmol H 2 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:CO 2 and Ar:CO 2 :N 2 , respectively, in comparison to cells incubated in Ar:CO 2 gas phase alone. Simultaneous production of H 2 and NH 4 + 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 H 2 evolution and NH 4 − excretion.