Characterization of Bacillus subtilis mutants resistant to cold shock-induced autolysis

Bacillus subtilis vegetative cells undergo autolysis when exposed to cold shock treatment. A mutant (CA1) resistant to cold shock was isolated, and its DNA was used for the transformation of B. subtilis 168AR. The transformant (TR1) and CA1 had almost completely lost major vegetative autolysins (CwlB and CwlG) and motility, and showed a filamentous cell morphology during the exponential phase. Expression of the sigD-lacZ fusion was reduced in TR1. But the introduction of a SigD overproducing plasmid, pHYSigD, into TR1 led to a considerable increase in the amount of autolysin, a normal cell morphology (short rod), and the cold shock-sensitive phenotype. However, motility was not restored in the transformant. The roles of pleiotropic genes in cold shock-induced autolysis are discussed.