Abstract
The unicellular cyanobacterium Chroococcidiopsis thermalis CALU 758 growing photoautotrophically synthesised a hydrogenase which catalysed an in vivo H 2 uptake in the oxyhydrogen reaction at a significant rate and showed only low level of in vitro MV-dependent H 2 evolution. The in vitro hydrogenase activity was not induced under microaerobic or nitrate-limiting conditions. Some correlation observed between the two activities indicated that the same enzyme may be involved in both H 2 uptake and H 2 evolution. Heterologous Southern hybridisations, using cyanobacterial hup and hox DNA fragments as probes, showed the presence of sequences similar to hox (encoding for a bidirectional hydrogenase) in C. thermalis CALU 758 with no indication for the presence of any sequences corresponding to an uptake hydrogenase. Further molecular experiments, using specific primers directed against different conserved regions of the large subunit ( hoxH) of the bidirectional hydrogenase confirmed the presence of corresponding sequences in C. thermalis CALU 758. Low-stringency Southern hybridisations detected only one copy of hoxH within the genome of C. thermalis CALU 758.
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