Transcriptional regulation of the bidirectional hydrogenase by oxygen and light in twoAnabaenaspecies

Abstract

Anabaena variabilis ATCC 29413 and Anabaena PCC 7120 were grown in batch cultures with combined nitrogen source. The hox genes encoding the bidirectional hydrogenase were expressed at a relatively low level in the heterocyst-free filaments. Transcriptional regulation of the bidirectional hydrogenase in response to oxygen and light was found to be similar in the two closely related strains. Low oxygen tension caused c.100-fold induction of the hox genes. However, when the anaerobic cultures were incubated in darkness the hox transcript accumulation increased by one order of magnitude compared with the illuminated anaerobic cultures. In addition, darkness could also reversibly induce hox expression and was found to be a positive regulator of hox expression even in the presence of oxygen. These results imply a specific requirement for the bidirectional hydrogenase of Anabaena PCC 7120 and A. variabilis ATCC 29413 in darkness both in the presence and absence of oxygen.

Bioenergy production using Trichormus variabilis – a review

“…Hydrogenase enzymes play the main role in photolysis‐dependent hydrogen production as well as hydrogen utilization. There are two kinds of hydrogenase enzymes: (i) S‐Fe hydrogenase (known as reversible or soluble hydrogenase), encoded by hoxEFUYH genes, function in generating molecular hydrogen to reduce NAD required for CO 2 absorption in the ribulose bisphosphate cycle, and (ii) Ni‐ Fe hydrogenase (known as uptake or membrane hydrogenase), encoded by hupSL genes, which catalyzes electron transfer from molecular hydrogen to the respiratory chain. Theoretically, efficiency of H 2 production in direct photolysis is high (40.1%) but it is not practically feasible due to the high inhibitory effects of O 2 on the reversible hydrogenase …”