Biochemical and mutational analysis of spore cortex-lytic enzymes in the food spoiler Bacillus licheniformis

Abstract

Bacillus licheniformis is frequently associated with food spoilage due to its ability to form highly resistant endospores. The present study reveals that B. licheniformis spore peptidoglycan shares a similar structure to spores of other species of Bacillus. Two enzymatic activities associated with depolymerisation of the cortical peptidoglycan, which represents a crucial step in spore germination, were detected by muropeptide analysis. These include lytic transglycosylase and N-acetylglucosaminidase activity, with non-lytic epimerase activity also being detected. The role of various putative cortex-lytic enzymes that account for the aforementioned activity was investigated by mutational analysis. These analyses indicate that SleB is the major lysin involved in cortex depolymerisation in B. licheniformis spores, with CwlJ and SleL having lesser roles. Collectively, the results of this work indicate that B. licheniformis spores employ a similar approach for cortical depolymerisation during germination as spores of other Bacillus species.

Keywords: Bacillus licheniformis; Cortex-lytic enzymes; Spore germination; Spore viability.