A pH-Dependent Gene Expression Enables Bacillus amyloliquefaciens MBNC to Adapt to Acid Stress

Acid tolerance response (ATR), a process by which bacteria optimize their growth conditions for cellular functions, is a well-characterized bacterial stress response. A bacterial isolate identified, as Bacillus amyloliquefaciens MBNC, was isolated from acidic soil and studied for its acid tolerance response under several range of acidic stress conditions imposed through inorganic acid, organic acid, acetate buffer, and soil extract. The ability of the B. amyloliquefaciens MBNC to tolerate extreme acidic conditions (pH 4.5) increased when exposed to moderate-acidic pH (pH 5.5). Along with ATR, the bacterial cell density was also critical to its ability to tolerate low pH as the cells of late log phase were more tolerant to low pH stress compared to the early log phase cells. A comparative expression study of 28 genes of B. amyloliquefaciens MBNC was assessed in cells grown in neutral (pH 7.0) and acidic condition (pH 4.5) through qRT-PCR. Among the 28 genes analyzed, 24 genes showed increased expression whereas the expression of 4 genes was downregulated under acid stress indicating to the involvement of the genes in acid stress response.