Department of Food Hygiene and Environmental Health, Faculty of Veterinary Medicine, University of Helsinki, Helsinki, Finland.
Int J Food Microbiol. 2011 Aug 15;148(3):177-83. doi: 10.1016/j.ijfoodmicro.2011.05.022. Epub 2011 Jun 2.
While temperature-dependent induction of flagella is a well-characterized phenomenon in Listeria monocytogenes, the essentiality of increased flagellum production during growth at low temperatures remains unclear. To study this relationship, we compared the relative expression levels of two motility genes, flhA and motA, at 3°C, 25°C and 37°C in L. monocytogenes strain EGD-e by using qRT-PCR, and compared the growth curves, motility, and flagellation between the wild-type and flhA and motA deletion mutants. The relative expression levels of flhA and motA at 3°C were significantly higher than at 37°C (p<0.01). At 3°C, the level of flhA transcripts was also significantly higher than at 25°C (p<0.01). Growth curve analysis showed that at 3°C both the growth rates and maximum optical densities of ΔflhA and ΔmotA strains at 600 nm were significantly lower than those of the wild-type (p<0.001), while no significant differences were observed between the wild-type and the mutants at 37°C, and 25°C. Mutant strains ΔflhA and ΔmotA were nonmotile at all three temperatures. At 25°C, the number of flagellated cells of ΔmotA was notably reduced compared with the wild-type, whereas ΔflhA appeared nonflagellated at all temperatures. The results suggest that flhA and motA play a role in the cold tolerance of L. monocytogenes strain EGD-e, and that motile flagella may be needed for optimal cold stress response of L. monocytogenes.
尽管在李斯特菌中，温度依赖性的鞭毛诱导是一个特征明显的现象，但在低温下增加鞭毛产生的必要性仍不清楚。为了研究这种关系，我们通过 qRT-PCR 比较了 L. monocytogenes 菌株 EGD-e 在 3°C、25°C 和 37°C 时两个运动基因 flhA 和 motA 的相对表达水平，并比较了野生型和 flhA 和 motA 缺失突变体之间的生长曲线、运动性和鞭毛形成。在 3°C 时，flhA 和 motA 的相对表达水平明显高于 37°C（p<0.01）。在 3°C 时，flhA 转录物的水平也明显高于 25°C（p<0.01）。生长曲线分析表明，在 3°C 时，ΔflhA 和 ΔmotA 菌株的生长速率和 600nm 时的最大光密度均明显低于野生型（p<0.001），而在 37°C 和 25°C 时，野生型和突变体之间没有观察到显著差异。突变株 ΔflhA 和 ΔmotA 在所有三个温度下均不运动。在 25°C 时，ΔmotA 的鞭毛细胞数量明显少于野生型，而在所有温度下，ΔflhA 似乎都没有鞭毛。结果表明，flhA 和 motA 在李斯特菌 EGD-e 的耐寒性中发挥作用，运动性鞭毛可能是李斯特菌对冷应激反应的最佳需要。
