MOLECULAR MECHANISM OF BACTERIAL SPORE GERMINATION

细菌孢子萌发是指从休眠孢子分化为营养细胞的过程，包括两个主要的生化事件：对萌发物作出反应的感官反应和皮层裂解酶对皮层(孢子肽聚糖)层的水解性反应。本研究对裂解酶激活过程的机理和发芽装置的构建进行了研究，获得了以下结果：(1)不同于产气荚膜梭菌SleM具有溶菌胺酶的功能，蜡状芽孢杆菌芽胞中的一种新的皮层裂解酶SLEL具有N-乙酰氨基葡萄糖苷酶的功能，它攻击部分降解的非应激皮质。(2)。蜡样芽孢杆菌编码酰胺酶的转录受Sigma G调控，在孢子发育的第III期在前孔中合成Slib。相反，产气荚膜梭菌SLEC(酰胺酶)和SleM在孢子发育的第三阶段在母细胞间表达。(3)。蜡状芽孢杆菌和产气荚膜假单胞菌的全部菌柄和菌盖均位于休眠孢子的皮层外侧。这些结果明确地表明，萌发隔离是以物种特有的方式构建的。(4)。产气荚膜梭菌SLEC的N末端前序列作为分子内伴侣，帮助分子的其余部分折叠。(5)。产气荚膜梭菌SLEC在萌发过程中被一组丝氨酸蛋白酶CSPA、B和C激活，并发现SLEC和CSP基因形成一个完全排列的簇。

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.