Regulation of nitrogen metabolism, starch utilisation and the β-hbd—adh1 gene cluster in Clostridium acetobutylicum

The successful genetic manipulation of Clostridium acetobutylicum for the increased production of solvents will depend on an understanding of gene structure and regulation in the bacterium. The glutamine synthetase (glnA) gene is regulated by antisense RNA, transcribed from a downstream promoter, in the opposite direction to the glnA gene. An open reading frame (ORF) was detected downstream of the glnA gene, which has sequence homology to response regulators with anti-termination activity and may be involved in sensing nitrogen conditions. The expression of the linked β-hbd, adh1 and fixB genes was investigated throughout the bacterial growth cycle by RNA hybridisation techniques. The adh1 gene was independently expressed as a 2.4-kb transcript which peaked at 12 h, immediately prior to the solventogenic phase. The β-hbd and fixB genes were transcribed throughout the acidogenic and solventogenic phases. A regulator gene, regA, which complements a Bacillus subtilis ccpA mutant, has been identified and sequenced from C. acetobutylicum P262. The regA gene repressed the degradation of starch by an uncharacterised C. acetobutylicum gene, and may therefore play a role in the utilisation of carbohydrate substrates in this organism.