低温下阻遏蛋白MogR对单增李斯特菌鞭毛形成的影响

Role of repressor MogR in flagellar biosynthesis of Listeria monocytogenes at low temperatures

摘要:

【目的】单核细胞增生李斯特菌(简称单增李斯特菌) (Listeria monocytogenes, Lm)是食源性病原菌，可以引发李斯特菌病(listeriosis)。Lm能在低温下生长，对冷藏食品的安全构成严重威胁，并对人类健康造成潜在的危害。Lm能低温生长与抑制鞭毛基因表达以减少鞭毛的合成有关。MogR是Lm鞭毛基因转录的阻遏蛋白，在机体里或37 ℃环境下具有阻遏作用，Lm不产生鞭毛；然而，当Lm处于20-0 ℃时MogR无阻遏作用，Lm产生鞭毛。我们研究发现在4 ℃生长条件下Lm鞭毛合成减少，但具体的分子机制尚未明确。本文探究在4 ℃下Lm鞭毛合成少与MogR起阻遏作用的关系。【方法】以Lm ATCC 19115为亲本株，分别构建了MogR和鞭毛丝蛋白FlaA的缺失株ΔmogR和ΔflaA (作为无鞭毛对照株)及其回补株cΔmogR和cΔflaA，测定了菌株在4、28、37 ℃时的运动性、鞭毛产生情况和鞭毛基因表达量，并对所构建的菌株进行了4、28、37 ℃时生长曲线的测定。【结果】在4 ℃时，mogR缺失后，菌株运动性显著强于亲本株(P<0.01)，鞭毛合成量显著多于亲本株(P<0.001)，鞭毛基因转录水平显著高于亲本株(P<0.001)；缺失株ΔmogR的生长能力显著弱于亲本株(P<0.05)。回补株cΔmogR的运动能力、鞭毛合成量和鞭毛基因转录水平与亲本株相比，无显著性差异。【结论】在4 ℃时，Lm鞭毛产量少与MogR对鞭毛基因起转录抑制作用有关，低温条件下Lm能生长繁殖与MogR对鞭毛基因表达的抑制作用有关。本研究结果为揭示Lm低温生长机制提供了新的信息。

Abstract:

[Objective] Listeria monocytogenes (Lm) is a ubiquitous foodborne pathogen causing listeriosis. Lm can grow at low temperatures and thus may cause safety problems of refrigerated food and threaten the public health. The growth of Lm at low temperatures involves the inhibition of flagellar gene expression, which restricts flagellar biosynthesis. MogR is a transcriptional repressor which represses the expression of flagellar genes during intracellular infection and during extracellular growth of Lm at 37 ℃, resulting in no biosynthesis of flagella. Whereas MogR is deprived of repression function and the bacteria produce flagella during growth at 20–30 ℃. Our studies demonstrated that Lm significantly reduced the flagellar production at 4 ℃, but the molecular mechanism of which remained unclear. This study aims to reveal the relationship between the reduction of flagella and MogR repression at 4 ℃. [Methods] We constructed the mogR-deleted mutant ΔmogR and the flagellin gene flaA-deleted mutant ΔflaA (as the control strain with no flagella), and their complementary strains cΔmogR and cΔflaA with the Lm strain ATCC 19115 as the parental strain. Then, we analyzed the swarming motility, flagellar biosynthesis, and transcriptional levels of flagellar genes in above five strains at 4 ℃, 28 ℃, and 37 ℃, respectively. The growth curves of these strains were determined at 4 ℃, 28 ℃, and 37 ℃, respectively. [Results] Compared with the parental strain, ΔmogR showed significantly increased in motility, flagellar biosynthesis, and transcriptional levels of flagellar genes (P<0.01, 0.001, and 0.001, respectively) at 4 ℃. The growth of ΔmogR markedly decreased compared with the parental strain (P<0.05) at 4 ℃. The data of motility, flagellar biosynthesis, and transcriptional levels of flagellar genes in cΔmogR had no significant differences compared with the parental strain. [Conclusion] The reduction in flagellar biosynthesis was associated with the repression function of MogR in Lm at 4 ℃. The reduction in flagellar biosynthesis was of benefit to Lm proliferation at low temperatures. This study enriched our understanding of the mechanism of Lm growth at low temperatures.