A New Physiological Role for CcpA in Adaptation of Bacillus Subtilis to Sugar-Induced Osmotic Stress

The model Gram-positive bacterium Bacillus subtilis is liable to be exposed to high-salinity environments in its natural habitats and is often used in fermentation with high concentrations of glucose or other sugars. High salinity or high concentrations of sugars can cause osmotic stress to B. subtilis [1]. The saltinduced osmotic stress can activate signalling pathways to induce expression of genes for biosynthesis or uptake of osmotically compatible solutes, thus protecting B. subtilis cells against the salt stress. Glycine betaine and proline are two important compatible solutes that can be utilized by B. subtilis to cope with salt stress [2]. The salt-inducible opuA operon encodes an ABC transporter that is involved in the uptake of glycine betaine for defense of B. subtilis against salt stress [3]. OpuE is a proline uptake transporter that can be induced by high salinity for osmotolerance [4]. The saltinducible proHJ operon encodes enzymes involved in biosynthesis of proline for osmotic adaptation [1]. The two-component signal transduction system DegSU can sense high salinity and be induced by salt stress. The response regulator DegU is a positive regulator of the osmotic response. Mutation of degU confers an osmosensitive phenotype to B. subtilis [5,6].