LuxS facilitates environmental adaptability and competition capability of avian pathogenic Escherichia coli.

Avian pathogenic Escherichia coli (APEC) severely impedes the development of the poultry industry and poses a serious threat to public health. The LuxS affects physiological processes such as bacterial virulence, biofilm formation, environmental adaptability, and motility. However, the effects of the LuxS on the environmental adaptability of APEC are not fully understood. Our study aims to investigate the effects of the LuxS on the environmental adaptability of APEC. Thus, the luxS gene mutant and complemented strains of APEC were constructed and characterized. We found that the mutant strain ΔluxS exhibited impaired adaptability to environmental stress, including oxidative, acid, base, heat, and hyperosmotic stress, with corresponding downregulation of stress-responsive genes. For oxidative stress tolerance, marA, fldA, and the rseC gene in the SoxR reduction system showed reduced expression. Genes regulating membrane and acid-base homeostasis, pH-inducible proteins, and the EvgS/EvgA two-component system were downregulated for acid-base stress. Genes related to osmoprotectant synthesis, uptake, potassium regulation, and heat stress adaptability, including extra cytoplasmic stress response (ESR), also exhibited lower transcriptional levels. Furthermore, we found that the ΔluxS mutant strain was impaired in competition capability due to downregulation of type VI secretion system (T6SS) genes. In addition, the mutant strain exhibited lower outer membrane permeability and lower proton motive force (PMF) compared with the wild-type strain. In conclusion, these findings indicate that the LuxS plays a critical role in regulating environmental adaptability, competition capability, outer membrane permeability, and PMF maintenance in APEC.