Transcriptional Regulation of Alcaligenes eutrophus Hydrogenase Genes

Alcaligenes eutrophus H16 produces a soluble hydrogenase (SH) and a membrane-bound hydrogenase (MBH) which catalyze the oxidation of H(2), supplying the organism with energy for autotrophic growth. The promoters of the structural genes for the SH and the MBH, P(SH) and P(MBH), respectively, were identified by means of the primer extension technique. Both promoters were active in vivo under hydrogenase-derepressing conditions but directed only low levels of transcription under conditions which repressed hydrogenase synthesis. The cellular pools of SH and MBH transcripts under the different growth conditions correlated with the activities of the respective promoters. Also, an immediate and drastic increase in transcript pool levels occurred upon derepression of the hydrogenase system. Both promoters were dependent on the minor sigma factor ς(54) and on the hydrogenase regulator HoxA in vivo. P(SH) was stronger than P(MBH) under both heterotrophic and autotrophic growth conditions. The two promoters were induced at approximately the same rates upon derepression of the hydrogenase system in diauxic cultures. The response regulator HoxA mediated low-level activation of P(SH) and P(MBH) in a heterologous system.