Department of Microbiology and Molecular Genetics, Michigan State University , East Lansing, Michigan, USA.
J Bacteriol. 2023 Oct 26;205(10):e0018123. doi: 10.1128/jb.00181-23. Epub 2023 Oct 4.
A suite of molecular sensory systems enables to control growth, development, and reproduction in response to levels of essential elements. The bacterial enhancer-binding protein (bEBP) NtrC and its cognate sensor histidine kinase, NtrB, are key regulators of nitrogen assimilation in many bacteria, but their roles in metabolism and development are not well defined. Notably, NtrC is an unconventional bEBP that lacks the σ-interacting loop commonly known as the GAFTGA motif. Here we show that deletion of slows cell growth in complex medium and that and are essential when ammonium is the sole nitrogen source due to their requirement for glutamine synthetase expression. Random transposition of a conserved IS3-family mobile genetic element frequently rescued the growth defect of mutant strains by restoring transcription of the operon, revealing a possible role for IS3 transposition in shaping the evolution of populations during nutrient limitation. We further identified dozens of direct NtrC-binding sites on the chromosome, with a large fraction located near genes involved in polysaccharide biosynthesis. The majority of binding sites align with those of the essential nucleoid-associated protein, GapR, or the cell cycle regulator, MucR1. NtrC is therefore predicted to directly impact the regulation of cell cycle and cell development. Indeed, loss of NtrC function led to elongated polar stalks and elevated synthesis of cell envelope polysaccharides. This study establishes regulatory connections between NtrC, nitrogen metabolism, polar morphogenesis, and envelope polysaccharide synthesis in . IMPORTANCE Bacteria balance cellular processes with the availability of nutrients in their environment. The NtrB-NtrC two-component signaling system is responsible for controlling nitrogen assimilation in many bacteria. We have characterized the effect of and deletion on growth and development and uncovered a role for spontaneous IS element transposition in the rescue of transcriptional and nutritional deficiencies caused by mutation. We further defined the regulon of NtrC, a bacterial enhancer-binding protein, and demonstrate that it shares specific binding sites with essential proteins involved in cell cycle regulation and chromosome organization. Our work provides a comprehensive view of transcriptional regulation mediated by a distinctive NtrC protein, establishing its connection to nitrogen assimilation and developmental processes in .
一套分子感应系统使 能够响应必需元素的水平来控制生长、发育和繁殖。细菌增强子结合蛋白 (bEBP) NtrC 和其同源传感器组氨酸激酶 NtrB 是许多细菌中氮同化的关键调节剂，但它们在 代谢和发育中的作用尚未得到很好的定义。值得注意的是，NtrC 是一种非常规的 bEBP，缺乏通常称为 GAFTGA 基序的 σ 相互作用环。在这里，我们表明缺失 会减缓复杂培养基中的细胞生长，并且当铵是唯一的氮源时， 和 是必需的，因为它们需要谷氨酰胺合成酶的表达。保守的 IS3 家族移动遗传元件的随机转座经常通过恢复 操纵子的转录来挽救 突变株的生长缺陷，揭示了 IS3 转座在营养限制期间塑造 种群进化中的可能作用。我们进一步在 染色体上鉴定了数十个直接的 NtrC 结合位点，其中很大一部分位于涉及多糖生物合成的基因附近。大多数结合位点与必需核相关蛋白 GapR 或细胞周期调节剂 MucR1 的结合位点对齐。因此，NtrC 被预测直接影响细胞周期和细胞发育的调节。事实上，NtrC 功能的丧失导致极柄伸长和细胞包膜多糖合成升高。这项研究建立了 NtrC、氮代谢、极性形态发生和 包膜多糖合成之间的调控联系。重要的是，细菌在其环境中的营养可用性与细胞过程之间取得平衡。NtrB-NtrC 双组分信号系统负责控制许多细菌中的氮同化。我们已经描述了 和 缺失对 生长和发育的影响，并发现自发 IS 元件转座在挽救由 突变引起的转录和营养缺陷方面的作用。我们进一步定义了 NtrC 的调控子，一种细菌增强子结合蛋白，并证明它与参与细胞周期调控和染色体组织的必需蛋白具有特定的结合位点。我们的工作提供了由独特的 NtrC 蛋白介导的转录调节的综合视图，确定了它与氮同化和 发育过程的联系。
