INRA, UMR1319 Micalis, Domaine de Vilvert, Jouy-en-Josas, France.
Appl Environ Microbiol. 2012 Apr;78(8):2553-61. doi: 10.1128/AEM.07446-11. Epub 2012 Feb 3.
The Bacillus cereus sensu lato complex has recently been divided into several phylogenetic groups with clear differences in growth temperature range. However, only a few studies have investigated the actual pathogenic potential of the psychrotolerant strains of the B. cereus group at low temperature, and little information is available concerning gene expression at low temperature. We found that vegetative cells of the psychrotolerant B. weihenstephanensis strain KBAB4 were pathogenic against the model insect Galleria mellonella at 15°C but not at 30°C. A similar temperature-dependent difference also was observed for the supernatant, which was cytotoxic to Vero epithelial cell lines and to murine macrophage J774 cells at 15°C but not at 30°C. We therefore determined the effect of low temperature on the production of various proteins putatively involved in virulence using two-dimensional protein gel electrophoresis, and we showed that the production of the Hbl enterotoxin and of two proteases, NprB and NprP2, was greater at a growth temperature of 15°C than at 30°C. The quantification of the mRNA levels for these virulence genes by real-time quantitative PCR at both temperatures showed that there was also more mRNA present at 15°C than at 30°C. We also found that at 15°C, hbl mRNA levels were maximal in the mid- to late exponential growth phase. In conclusion, we found that the higher virulence of the B. cereus KBAB4 strain at low temperature was accompanied by higher levels of the production of various known PlcR-controlled virulence factors and by a higher transcriptional activity of the corresponding genes.
细菌芽孢杆菌感观复杂最近被分为几个进化群，在生长温度范围上有明显的差异。然而，只有少数研究调查了低温下芽孢杆菌属中耐寒菌株的实际致病潜力，而且有关低温下基因表达的信息很少。我们发现，耐寒的芽孢杆菌菌株 KBAB4 的营养细胞在 15°C 时对模式昆虫家蚕具有致病性，但在 30°C 时则没有。同样的温度依赖性差异也观察到在超滤液中，该超滤液在 15°C 时对 Vero 上皮细胞系和鼠巨噬细胞 J774 细胞具有细胞毒性，但在 30°C 时则没有。因此，我们使用二维蛋白质凝胶电泳来确定低温对各种假定与毒力有关的蛋白质的产生的影响，我们表明 Hbl 肠毒素和两种蛋白酶 NprB 和 NprP2 的产生在 15°C 时比在 30°C 时更高。实时定量 PCR 在这两种温度下对这些毒力基因的 mRNA 水平的定量表明，15°C 时的 mRNA 也更多。我们还发现，在 15°C 时，hbl mRNA 水平在中到晚期指数生长期达到最大值。总之，我们发现，芽孢杆菌 KBAB4 菌株在低温下更高的毒力伴随着各种已知 PlcR 控制的毒力因子的更高水平的产生和相应基因的更高转录活性。
