North Hunter, McLaughlin Maeve, Fiebig Aretha, Crosson Sean
Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan USA.
bioRxiv. 2023 Aug 31:2023.06.06.543975. doi: 10.1101/2023.06.06.543975.
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 σ54-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 (glnA) 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 .
一套分子传感系统能够根据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及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因子，但其在代谢和发育中的作用尚未明确界定。值得注意的是，NtrC是一种非常规的bEBP，缺乏通常称为GAFTGA基序的与σ54相互作用的环。在这里，我们表明缺失会减缓复杂培养基中的细胞生长，并且当铵是唯一氮源时，由于它们对谷氨酰胺合成酶（glnA）表达的需求，和是必不可少的。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菌株的生长缺陷，揭示了IS3转座在营养限制期间塑造群体进化中的可能作用。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参与多糖生物合成的基因附近。大多数结合位点与必需的类核相关蛋白GapR或细胞周期调节因子MucR1的结合位点一致。因此，预计NtrC会直接影响细胞周期和细胞发育的调节。事实上，NtrC功能的丧失导致极性茎伸长和细胞包膜多糖合成增加。这项研究在中建立了NtrC、氮代谢、极性形态发生和包膜多糖合成之间的调节联系。
