Acidification of Culture Medium by Products of Glucose Metabolism Inhibit Synthesis of Heterologous Extracellular α-Amylase by <i>Bacillus subtilis 168</i>
The synthesis of α-amylase AmyM3 from <i>B. flexus</i> 406 in recombinant strain <i>B. subtilis</i> 168-28 was significantly repressed during submerged cultivation in nutrient medium supplemented with 1% glucose. Repression of α-amylase synthesis by glucose in <i>B. subtilis</i> cells observed at the level of transcription and mediated by catabolite control protein CcpA. After deletion of putative <i>cre</i> site in the <i>amyM3</i> gene the effect of catabolite repression was eliminated, but the amount of extracellular α-amylase still significantly decreased in the presence of glucose. It was shown that a shift of the cultivation medium pH to 5.8–6.0, caused by glucose overflow metabolites excreted by <i>B. subtilis</i>, despite the high level of <i>amyM3</i> gene activity, interferes with the synthesis of active extracellular α-amylase, probably affecting post-secretory folding of the enzyme. This o-bservation is a newly demonstrated facet of CcpA-mediated influence of preferentially utilized sugars on e-xtracellular α-amylase production in <i>Bacillus subtilis</i>.