Transcriptional regulation of Nostoc uptake hydrogenase

Filamentous, heterocystous cyanobacteria may contain both an uptake hydrogenase (encoded by hupSL) and a bidirectional enzyme (encoded by hoxFUYH). The present study identifies three strains (Anabaena variabilis, Nostoc muscorum and Nostoc sp. strain PCC 73102) with a contiguous hupL in both vegetative cells and heterocysts. The two Nostoc strains differ in either containing a bidirectional enzyme (N. muscorum) or lacking this enzyme (N. PCC 73102). Transcriptional studies, using reverse transcriptase-polymerase chain reaction, demonstrated an induction of a hupL transcript approximately 24 h after a shift from non-nitrogen-fixing to nitrogen-fixing conditions (in parallel with the induction of an in vivo light-dependent H2-uptake activity) in N. muscorum. However, the level of hoxH transcripts did not change significantly during the induction of the H2-uptake activity.