ANAEROBIC REGULATION OF THE HYDROGENASE-1 (HYA) OPERON OF ESCHERICHIA-COLI

Using a transcriptional fusion to the lacZ gene, we have analyzed the anaerobic regulation of the hydrogenase 1 (hya) operon in response to different anaerobic growth conditions and to mutations in regulatory g enes. We found that the transcription of the hya operon was induced wh en the growth condition was changed from aerobic to anaerobic and that this induction was independent of Fnr but dependent on regulators App Y and ArcA. Furthermore, we found that the transcription of the hya op eron was not regulated by the cyclic AMP-cyclic AMP receptor protein c omplex. Investigation of the effects of different anaerobic growth con ditions on the expression of the hya operon showed that expression was induced by formate and repressed by nitrate. Formate induction was no t mediated by the fhlA gene product, and nitrate repression was not me diated by the narL gene product. We found a high level of anaerobic ex pression of the hya operon in glucose medium supplemented with formate and in glycerol medium supplemented with fumarate, suggesting that hy drogenase isoenzyme 1 has a function during both fermentative growth a nd anaerobic respiration.