New insights into the formation and recovery of sublethally injured Escherichia coli O157:H7 induced by lactic acid

Escherichia coli O157:H7 can survive as the state of sublethal injury in lactic acid and injured cells can be recovered under suitable condition. In this study, RNA sequencing analysis revealed the overall genes change of sublethally injured and initial recovered cells. Compared with untreated samples, 53 up-regulated and 98 down-regulated differentially expressed genes were found in SI. Meanwhile, Genes related to carbohydrate transport and metabolic were up-regulated and the addition of carbohydrate increased cells resistance to LA. Genes involved in osmotic stress response and cell membrane integrity were down-regulated and E. coli O157:H7 cells were sensitive to osmotic stress during sublethal injury formation. Genes related to iron stress response and cation transport were changed and cation may affect sublethal injury formation by influencing production of ROS and cellular processes. In R, 1370 up-regulated and 1110 down-regulated DEGs were subdivided into various GO terms and membrane, biological adhesion, cell projection, oxidation-reduction process and catalytic activity, etc., showed significant enrichment. Particularly, genes related to fimbrial, flagellum and type III secretion system were up-regulated, which may improve infection ability and virulence property during recovery of injured cells. These findings provide novel insights into formation and recovery of sublethally injured E. coli O157:H7 induced by LA.

大肠杆菌O157:H7（Escherichia coli O157:H7）可在乳酸（lactic acid, LA）环境中以亚致死损伤状态存活，且受损细胞可在适宜条件下完成恢复。本研究通过RNA测序（RNA Sequencing）分析，揭示了亚致死损伤细胞与初始恢复态细胞的全基因表达变化特征。与未处理样本相比，亚致死损伤组（SI）共鉴定得到53个上调差异表达基因（Differentially Expressed Genes, DEGs）、98个下调差异表达基因。其中，碳水化合物转运与代谢相关基因呈上调表达，外源添加碳水化合物可增强菌体对乳酸的耐受性；渗透应激响应及细胞膜完整性相关基因则呈下调表达，且该菌在亚致死损伤形成过程中对渗透应激敏感；铁应激响应与阳离子转运相关基因表达发生改变，阳离子可能通过影响活性氧（Reactive Oxygen Species, ROS）的生成及细胞生理过程，参与调控亚致死损伤的形成。在恢复组（R）中，1370个上调DEGs与1110个下调DEGs被富集至各类基因本体（Gene Ontology, GO）条目，膜结构、生物黏附、细胞突起、氧化还原过程及催化活性等条目呈现显著富集。尤为关键的是，菌毛、鞭毛及三型分泌系统（Type III Secretion System）相关基因呈上调表达，这可能在受损细胞恢复阶段提升菌体的侵染能力与毒力特性。本研究结果为乳酸诱导的大肠杆菌O157:H7亚致死损伤的形成与恢复机制提供了全新的研究视角。