Responses of Bacillus subtilis to Hypotonic Challenges: Physiological Contributions of Mechanosensitive Channels to Cellular Survival

• DOI: 10.1128/aem.01573-07
• Publication Date: 2008-03-01T02:37:03Z
• Authors: Tamara Hoffmann; Clara Boiangiu; Susanne Moses; Erhard Bremer
• Keywords: Betaine; Mutagenesis, Insertional; 0303 health sciences; 03 medical and health sciences; Microbial Viability; Bacterial Proteins; Osmotic Pressure; Gene Order; Mechanotransduction, Cellular; Gene Deletion; Ion Channels; Bacillus subtilis

ABSTRACT

Mechanosensitive channels are thought to function as safety valves for the release of cytoplasmic solutes from cells that have to manage a rapid transition from high- to low-osmolarity environments. Subsequent to an osmotic down-shock of cells grown at high osmolarity, Bacillus subtilis rapidly releases the previously accumulated compatible solute glycine betaine in accordance with the degree of the osmotic downshift. Database searches suggest that B. subtilis possesses one copy of a gene for a mechanosensitive channel of large conductance ( mscL ) and three copies of genes encoding proteins that putatively form mechanosensitive channels of small conductance ( yhdY , yfkC , and ykuT ). Detailed mutational analysis of all potential channel-forming genes revealed that a quadruple mutant ( mscL yhdY yfkC ykuT ) has no growth disadvantage in high-osmolarity media in comparison to the wild type. Osmotic down-shock experiments demonstrated that the MscL channel is the principal solute release system of B. subtilis , and strains with a gene disruption in mscL exhibited a severe survival defect upon an osmotic down-shock. We also detected a minor contribution of the SigB-controlled putative MscS-type channel-forming protein YkuT to cellular survival in an mscL mutant. Taken together, our data revealed that mechanosensitive channels of both the MscL and MscS types play pivotal roles in managing the transition of B. subtilis from hyper- to hypo-osmotic environments.