MOST-USDA Joint Research Center for Food Safety, School of Agriculture & Biology, and State Key Lab of Microbial Metabolism, Shanghai Jiao Tong University, Shanghai, 200240, China.
College of Food Science and Engineering, Northwest Agriculture and Forestry University, Yangling, 712100, Shaanxi, China.
BMC Genomics. 2021 Jul 5;22(1):507. doi: 10.1186/s12864-021-07759-z.
Salmonella is a major bacterial pathogen associated with a large number of outbreaks of foodborne diseases. Many highly virulent serovars that cause human illness belong to Salmonella serogroup C1, and Salmonella ser. Choleraesuis is a prominent cause of invasive infections in Asia. Comparative genomic analysis in our previous study showed that two homologous genes, SC0368 and SC0595 in Salmonella ser. Choleraesuis were unique to serogroup C1. In this study, two single-deletion mutants (Δ0368 and Δ0595) and one double-deletion mutant (Δ0368Δ0595) were constructed based on the genome. All these mutants and the wild-type strain were subjected to RNA-Seq analysis to reveal functional relationships of the two serogroup C1-specific genes.
Data from RNA-Seq indicated that deletion of SC0368 resulted in defects in motility through repression of σ in flagellar regulation Class 3. Consistent with RNA-Seq data, results from transmission electron microcopy (TEM) showed that flagella were not present in △0368 and △0368△0595 mutants resulting in both swimming and swarming defects. Interestingly, the growth rates of two non-motile mutants △0368 and △0368△0595 were significantly greater than the wild-type, which may be associated with up-regulation of genes encoding cytochromes, enhancing bacterial proliferation. Moreover, the △0595 mutant was significantly more invasive in Caco-2 cells as shown by bacterial enumeration assays, and the expression of lipopolysaccharide (LPS) core synthesis-related genes (rfaB, rfaI, rfaQ, rfaY, rfaK, rfaZ) was down-regulated only in the △0368△0595 mutant. In addition, this study also speculated that these two genes might be contributing to serotype conversion for Salmonella C1 serogroup based on their apparent roles in biosynthesis of LPS and the flagella.
A combination of biological and transcriptomic (RNA-Seq) analyses has shown that the SC0368 and SC0595 genes are involved in biosynthesis of flagella and complete LPS, as well as in bacterial growth and virulence. Such information will aid to revealing the role of these specific genes in bacterial physiology and evolution within the serogroup C1.
沙门氏菌是一种与大量食源性疾病暴发相关的主要细菌病原体。许多导致人类疾病的高毒力血清型属于 C1 血清群沙门氏菌，而 C1 血清群沙门氏菌肠炎亚种是亚洲侵袭性感染的主要原因。我们之前的比较基因组分析表明，C1 血清群沙门氏菌肠炎亚种中的两个同源基因 SC0368 和 SC0595 是独特的。在这项研究中，基于基因组构建了两个单缺失突变体（Δ0368 和 Δ0595）和一个双缺失突变体（Δ0368Δ0595）。对所有这些突变体和野生型菌株进行 RNA-Seq 分析，以揭示这两个 C1 血清群特异性基因的功能关系。
RNA-Seq 数据表明，SC0368 的缺失导致通过抑制鞭毛调节 Class 3 中的 σ 导致运动能力缺陷。与 RNA-Seq 数据一致，透射电子显微镜（TEM）结果表明，在 △0368 和 △0368△0595 突变体中不存在鞭毛，导致游动和群集缺陷。有趣的是，两个非运动突变体 △0368 和 △0368△0595 的生长速度明显快于野生型，这可能与细胞色素编码基因的上调有关，增强了细菌的增殖。此外，细菌计数测定显示，△0595 突变体在 Caco-2 细胞中的侵袭性明显更强，而 LPS 核心合成相关基因（rfaB、rfaI、rfaQ、rfaY、rfaK、rfaZ）的表达仅在 △0368△0595 突变体中下调。此外，本研究还推测，基于它们在 LPS 和鞭毛生物合成中的明显作用，这两个基因可能有助于 C1 血清群沙门氏菌的血清型转换。
生物和转录组学（RNA-Seq）分析的结合表明，SC0368 和 SC0595 基因参与鞭毛和完整 LPS 的生物合成，以及细菌的生长和毒力。这些信息将有助于揭示这些特定基因在 C1 血清群细菌生理学和进化中的作用。
