The Threshold Level of the Sensor Histidine Kinase KinA Governs Entry into Sporulation in Bacillus subtilis
The Threshold Level of the Sensor Histidine Kinase KinA Governs Entry into Sporulation in Bacillus subtilis
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DOI：
10.1128/jb.00466-10
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发表时间：
2010-08-01
影响因子：
3.2
通讯作者：
Fujita, Masaya
中科院分区：
文献类型：
--
作者：
Eswaramoorthy, Prahathees;Duan, Daniel;Fujita, Masaya
枯草芽孢杆菌中的孢子形成由一个复杂的基因调控回路控制，该基因调控回路在营养缺乏时被激活。最初的过程是由磷酸化介导的，涉及主要的孢子形成组氨酸激酶（KinA）和两个额外的磷酸转移酶（Spo 0 F和Spo 0 B），激活主转录因子Spo 0A。关于引发孢子形成的初始事件和机制知之甚少。使用一个菌株，其中合成的KinA是在IPTG（异丙基-β-D-硫代半乳糖苷）诱导型启动子的控制下，在这里，我们证明，诱导合成的KinA超过一定的水平，导致进入不可逆的孢子形成过程，而不管营养的可用性。此外，在与内源性kinA启动子相似但比内源性kinA启动子更强的sigma（H）依赖性启动子下表达KinA的工程化细胞在生长期间诱导孢子形成。这些细胞，我们命名为COS（组成型孢子形成）细胞，表现出孢子形成细胞的形态和特性，并在营养丰富的条件下表达孢子形成标记基因。因此，我们创建了一种工程菌株，该工程菌株显示两个细胞周期（生长和孢子形成）整合到一个周期中，而与培养条件无关，而在野生型中，根据营养物质的可用性做出适当的细胞命运决定。这些结果表明，主要孢子形成激酶的阈值水平作为决定细胞命运的分子开关，并可能排除KinA活性响应未知信号而调节的可能性。
Sporulation in Bacillus subtilis is controlled by a complex gene regulatory circuit that is activated upon nutrient deprivation. The initial process is directed by the phosphorelay, involving the major sporulation histidine kinase (KinA) and two additional phosphotransferases (Spo0F and Spo0B), that activates the master transcription factor Spo0A. Little is known about the initial event and mechanisms that trigger sporulation. Using a strain in which the synthesis of KinA is under the control of an IPTG (isopropyl-beta-D-thiogalactopyranoside)inducible promoter, here we demonstrate that inducing the synthesis of the KinA beyond a certain level leads to the entry of the irreversible process of sporulation irrespective of nutrient availability. Moreover, the engineered cells expressing KinA under a sigma(H)-dependent promoter that is similar to but stronger than the endogenous kinA promoter induce sporulation during growth. These cells, which we designated COS (constitutive sporulation) cells, exhibit the morphology and properties of sporulating cells and express sporulation marker genes under nutrient-rich conditions. Thus, we created an engineered strain displaying two cell cycles (growth and sporulation) integrated into one cycle irrespective of culture conditions, while in the wild type, the appropriate cell fate decision is made depending on nutrient availability. These results suggest that the threshold level of the major sporulation kinase acts as a molecular switch to determine cell fate and may rule out the possibility that the activity of KinA is regulated in response to the unknown signal(s).