MOLECULAR MECHANISM OF BACTERIAL SPORE GERMINATION

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Bacterial spore germination, which means a differentiation from dormant spores to vegetative cells, consists of two major biochemical events ; a sensory reaction which responds to germinants and a hydrolytic reaction of cortex (spore peptidoglycan) layer by cortex lytic enzymes. The present study was undertaken to understand mechanisms of activation process of the lytic enzymes and a construction of germination apparatus, and the following results were obtained.(1). Different from Clostridium perfringens SleM which function as muramidase, a novel cortex lytic enzyme SleL from Bacillus cereus spores acts as N-acetylglucosaminidase which attacks partially degraded unstressed cortex. (2). Transcription of B.cereus sleB which encodes amidase is regulated by sigma G, and SleB is synthesized in forespore compartment at stage III of developing spores. On the contrary, C.perfringens SleC (amidase) and SleM is expressed in mother cell compartment at stage III of developing spores. (3). All SleB and SleL of B.cereus and SleC and SleM of C.perfringens are located at the exterior side of cortex in the dormant spore. These results unequivocally indicate that germination aparatusis constructed in a species-specific manner. (4). The N-terminal presequence of C.perfringens SleC functions as intramolecular chaperone to assist folding of the remainder of molecule. (5). C.perfringens SleC is activated by a group of serineprotease CspA, B and C during germination, and sleC and csp genes were found to form a tandemly aligned cluster.