Mechanobiology Institute, National University of Singapore, T-Lab, 5A Engineering Drive 1, Singapore, 117411, Singapore.
Department of Physics, National University of Singapore, Singapore, 117551, Singapore.
Nat Commun. 2017 Nov 14;8(1):1587. doi: 10.1038/s41467-017-02030-0.
Unlike eukaryotes, bacteria undergo large changes in osmolality and cytoplasmic pH. It has been described that during acid stress, bacteria internal pH promptly acidifies, followed by recovery. Here, using pH imaging in single living cells, we show that following acid stress, bacteria maintain an acidic cytoplasm and the osmotic stress transcription factor OmpR is required for acidification. The activation of this response is non-canonical, involving a regulatory mechanism requiring the OmpR cognate kinase EnvZ, but not OmpR phosphorylation. Single cell analysis further identifies an intracellular pH threshold ~6.5. Acid stress reduces the internal pH below this threshold, increasing OmpR dimerization and DNA binding. During osmotic stress, the internal pH is above the threshold, triggering distinct OmpR-related pathways. Preventing intracellular acidification of Salmonella renders it avirulent, suggesting that acid stress pathways represent a potential therapeutic target. These results further emphasize the advantages of single cell analysis over studies of population averages.
与真核生物不同，细菌的渗透压和细胞质 pH 值会发生很大变化。据描述，在酸性胁迫下，细菌内部 pH 值迅速酸化，随后恢复。在这里，我们使用单活细胞中的 pH 成像技术表明，在酸性胁迫后，细菌维持酸性细胞质，渗透压应激转录因子 OmpR 是酸化所必需的。这种反应的激活是非经典的，涉及一种需要 OmpR 同源激酶 EnvZ 但不涉及 OmpR 磷酸化的调节机制。单细胞分析进一步确定了一个细胞内 pH 值阈值约为 6.5。酸性胁迫会降低低于该阈值的内部 pH 值，从而增加 OmpR 二聚体和 DNA 结合。在渗透压胁迫下，内部 pH 值高于阈值，触发不同的 OmpR 相关途径。防止沙门氏菌的细胞内酸化使其失去毒力，这表明酸应激途径可能是一个潜在的治疗靶点。这些结果进一步强调了单细胞分析相对于群体平均值研究的优势。
