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 B. flexus 406 in recombinant strain B. subtilis 168-28 was significantly repressed during submerged cultivation in nutrient medium supplemented with 1% glucose. Repression of α-amylase synthesis by glucose in B. subtilis cells observed at the level of transcription and mediated by catabolite control protein CcpA. After deletion of putative cre site in the amyM3 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 B. subtilis, despite the high level of amyM3 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 Bacillus subtilis.