Genetic requirements for induction of germination of spores of Bacillus subtilis by Ca2+-dipicolinate
Genetic requirements for induction of germination of spores of Bacillus subtilis by Ca2+-dipicolinate
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DOI：
10.1128/jb.183.16.4886-4893.2001
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发表时间：
2001-08-01
影响因子：
3.2
通讯作者：
Setlow, P
中科院分区：
文献类型：
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作者：
Paidhungat, M;Ragkousi, K;Setlow, P
休眠的枯草芽孢杆菌孢子可以被营养物质诱导发芽，也可以被非代谢的化学物质诱导发芽，如1:1的Ca2+和二吡啶酸（DPA）的螯合物。营养物质与孢子中的受体结合，这种结合触发孢子核心的事件，包括DPA排泄和再水化，并通过很大程度上未知的机制激活周围皮层的水解。由于Ca2+-DPA不需要受体来诱导孢子萌发，我们想知道这个过程是否利用了其他蛋白质，如假定的皮层裂解酶SleB和CwlJ，它们参与营养诱导的萌发。我们发现Ca2+-DPA通过首先激活cwlj依赖的皮质水解来触发萌发；这种机制不同于营养诱导的萌发，在营养诱导的萌发中，孢子核心的早期萌发事件不需要皮质水解。然而，由于营养物质可以诱导孢子在皮层水解之前释放DPA，我们研究了从核心分泌的DPA是否作为激活皮层中CwlJ的信号。事实上，营养诱导的CwlJ激活需要内源性DPA，外源性Ca2+-DPA可以部分弥补这一需求。因此，我们的研究结果定义了Ca2+- dpa诱导发芽的机制，并为激活皮层水解响应营养的信号通路提供了第一个明确的证据。
Dormant Bacillus subtilis spores can be induced to germinate by nutrients, as well as by nonmetabolizable chemicals, such as a 1:1 chelate of Ca2+ and dipicolinic acid (DPA). Nutrients bind receptors in the spore, and this binding triggers events in the spore core, including DPA excretion and rehydration, and also activates hydrolysis of the surrounding cortex through mechanisms that are largely unknown. As Ca2+-DPA does not require receptors to induce spore germination, we asked if this process utilizes other proteins, such as the putative cortex-lytic enzymes SleB and CwlJ, that are involved in nutrient-induced germination. We found that Ca2+-DPA triggers germination by first activating CwlJ-dependent cortex hydrolysis; this mechanism is different from nutrient-induced germination where cortex hydrolysis is not required for the early germination events in the spore core. Nevertheless, since nutrients can induce release of the spore's DPA before cortex hydrolysis, we examined if the DPA excreted from the core acts as a signal to activate CwlJ in the cortex. Indeed, endogenous DPA is required for nutrient-induced CwlJ activation and this requirement was partially remedied by exogenous Ca2+-DPA. Our findings thus define a mechanism for Ca2+-DPA-induced germination and also provide the first definitive evidence for a signaling pathway that activates cortex hydrolysis in response to nutrients.