Department of Microbiology, Harvard Medical School, Boston, Massachusetts, USA.
J Bacteriol. 2022 Feb 15;204(2):e0047021. doi: 10.1128/JB.00470-21. Epub 2021 Nov 15.
Bacterial spores can rapidly exit dormancy through the process of germination. This process begins with the activation of nutrient receptors embedded in the spore membrane. The prototypical germinant receptor in Bacillus subtilis responds to l-alanine and is thought to be a complex of proteins encoded by the genes in the operon: , , and . The GerAB subunit has recently been shown to function as the nutrient sensor, but beyond contributing to complex stability, no additional functions have been attributed to the other two subunits. Here, we investigate the role of GerAA. We resurrect a previously characterized allele of (termed ) that carries a mutation in and show that it constitutively activates germination even in the presence of a wild-type copy of . Using an enrichment strategy to screen for suppressors of , we identified mutations in all three genes that restore a functional receptor. Characterization of two distinct suppressors revealed that one ( reduces the GerA complex's ability to respond to l-alanine, while another () disrupts the germinant signal downstream of l-alanine recognition. These data argue against models in which GerAA is directly or indirectly involved in germinant sensing. Rather, our data suggest that GerAA is responsible for transducing the nutrient signal sensed by GerAB. While the steps downstream of have yet to be uncovered, these results validate the use of a dominant-negative genetic approach in elucidating the signal transduction pathway. Endospore formers are a broad group of bacteria that can enter dormancy upon starvation and exit dormancy upon sensing the return of nutrients. How dormant spores sense and respond to these nutrients is poorly understood. Here, we identify a key step in the signal transduction pathway that is activated after spores detect the amino acid l-alanine. We present a model that provides a more complete picture of this process that is critical for allowing dormant spores to germinate and resume growth.
细菌孢子可以通过发芽过程迅速从休眠中苏醒。这一过程始于嵌入孢子膜中的营养受体的激活。枯草芽孢杆菌中典型的发芽受体响应 l-丙氨酸，被认为是由 操纵子中编码的基因的蛋白质复合物： 、 和 。最近，GerAB 亚基被证明作为营养传感器发挥作用，但除了有助于复合物的稳定性外，尚未赋予其他两个亚基其他功能。在这里，我们研究了 GerAA 的作用。我们复活了以前表征的 （称为 ）的等位基因，该等位基因在 中携带突变，并且即使存在野生型拷贝，也表现出组成型激活发芽。使用富集策略筛选 的抑制剂，我们鉴定了三个 基因的突变，这些突变恢复了功能性受体。对两个不同的 抑制剂的特征描述表明，一个（ 降低了 GerA 复合物对 l-丙氨酸的响应能力，而另一个（ 破坏了 l-丙氨酸识别下游的发芽信号。这些数据反对 GerAA 直接或间接参与发芽感应的模型。相反，我们的数据表明，GerAA 负责转导由 GerAB 感知的营养信号。虽然 下游的步骤尚未被揭示，但这些结果验证了使用显性负遗传方法阐明 信号转导途径的有效性。内孢子形成菌是一组广泛的细菌，它们可以在饥饿时进入休眠状态，并在感知到营养物质返回时退出休眠状态。休眠孢子如何感知和响应这些营养物质还知之甚少。在这里，我们确定了在孢子检测到氨基酸 l-丙氨酸后激活的信号转导途径中的关键步骤。我们提出了一个模型，该模型提供了对这一过程的更完整描述，这对于允许休眠孢子发芽和恢复生长至关重要。
