A Novel Spore Peptidoglycan Hydrolase of Bacillus cereus : Biochemical Characterization and Nucleotide Sequence of the Corresponding Gene, sleL

Abstract

ABSTRACT The exudate of germinated spores of B. cereus IFO 13597 in 0.15 M KCl–50 mM potassium phosphate (pH 7.0) contained a spore-lytic enzyme which has substrate specificity for fragmented spore cortex from wild-type organisms (cortical-fragment-lytic enzyme [CFLE]), in addition to a previously characterized germination-specific hydrolase which acts on intact spore cortex (spore cortex-lytic enzyme [SCLE]) (R. Moriyama, S. Kudoh, S. Miyata, S. Nonobe, A. Hattori, and S. Makino, J. Bacteriol. 178:5330–5332, 1996). CFLE was not capable of degrading isolated cortical fragments from spores of Bacillus subtilis ADD1, which lacks muramic acid δ-lactam. This suggests that CFLE cooperates with SCLE in cortex hydrolysis during germination. CFLE was purified in an active form and identified as a 48-kDa protein which functions as an N -acetylglucosaminidase. Immunochemical studies suggested that the mature enzyme is localized on a rather peripheral region of the dormant spore, probably the exterior of the cortex layer. A gene encoding the enzyme, sleL , was cloned in Escherichia coli , and the nucleotide sequence was determined. The gene encodes a protein of 430 amino acids with a deduced molecular weight of 48,136. The N-terminal region contains a repeated motif common to several peptidoglycan binding proteins. Inspection of the data banks showed no similarity of CFLE with N -acetylglucosaminidases found so far, suggesting that CFLE is a novel type of N -acetylglucosaminidase. The B. subtilis genome sequence contains genes, yaaH and ydhD , which encode putative proteins showing similarity to SleL.