Effects of a novel pathogenicity-related gene product of Salmonella, SEp22, on the viability of Salmonella in its environments

进一步研究了从家禽养殖场分离的肠炎沙门氏菌病原菌中SEp22表达调控的机制。SEp22在Luria-Bertani培养基（LB）等营养丰富的培养基中的表达依赖于生长阶段，在对数期表达量很少，但在对数后期到平稳期表达量迅速增加。对SEp22 mRNA进行Northern blot和RT-PCR分析发现，SEp22 mRNA的表达量在SEp22蛋白合成之前增加，但在这些生长阶段，其表达量的增加略晚于RNA聚合酶σ因子σ32的表达量的增加。而σ70的表达与SEp22无关。通过将沙门氏菌转移到新鲜LB中循环重复SEp22的这些变化。相反，在M-9培养基等营养不良的培养基中培养时，即使在固定阶段也没有观察到SEp22的诱导，在M-9培养基中添加LB可以部分恢复SEp22。我们一直在研究LB中支持在这些条件下诱导SEp22的营养因子，并从这些因子中排除了葡萄糖或一些氨基酸。综上所述，这些结果表明SEp22的表达受到转录调控，沙门氏菌的环境分离物即使可能对宿主动物具有致病性，但由于缺乏SEp22的表达，在营养不良的环境中并不总是具有致病性。

Mechanisms underlying regulation of SEp22 expression were further studied in pathogenic strains of Salmonella Enteritidis, isolated from poultry farms. Expression of SEp22 was dependent on the growth phases in nutritionally enriched culture medium like Luria-Bertani medium(LB), and was scarce in logarithmic phase but became rapidly increased in late-logarithmic to stationary phases. Northern blot or RT-PCR analysis of SEp22 mRNA revealed that it increased prior to the synthesis of SEp22 protein but slightly later than the increase of RNA polymerase σ factor, σ32, expression in these growth phases. However, expression of σ70 was not related with SEp22. These changes in SEp22 were cyclically repeated by transferring Salmonella into fresh LB. In contrast, induction of SEp22 was not observed even in stationary phases when cultured in nutritionally poor medium like M-9 medium, which was in part restored by addition of LB to M-9 medium. We have been examining the nutrition factor(s) in LB which supports induction of SEp22 under these conditions, and have excluded glucose or some amino acids from such factor(s). Taken together, these results suggest that expression of SEp22 is transcriptionally regulated and that environmental isolate of Salmonella, even if it potentially causes pathogenicity to host animals, does not always become pathogenic in nutritionally poor environment due to lack of expression of SEp22.