Facultative H2-dependent anoxygenic photosynthesis in the unicellular cyanobacterium Gloeocapsa alpicola CALU 743

Abstract

When cells of the unicellular cyanobacterium Gloeocapsa alpicola CALU 743 are deprived of nitrate, the phycobilisomes are actively degraded by a proteolytic process termed chlorosis, which accompanied by decrease of rates of oxygen evolution and carbon dioxide fixation, increase of amount of stored glycogen and increase of hydrogenase activity. Suspensions of such cells exhibited a capacity for light-dependent inorganic carbon photoassimilation under anaerobic conditions in the presence of hydrogen and DCMU. The rate of 14C incorporation was commensurable with that for nitrate-sufficient cells at oxygenic photosynthesis and reached 35-38 μmol 14C h?1 mg?1 Chl a. Incubation of G. alpicola grown aerobically in the presence of limiting concentrations of nitrate under anaerobic conditions (Ar, CO2, DCMU) in the light with addition of nitrate and H2, resulted in the increase of cellular protein, evidencing that G. alpicola cells with high level of hydrogenase activity are able to perform H2-dependent anoxygenic photosynthesis at levels supporting the growth of this cyanobacterium.