The cross-regulation between two-component system BasS/BasR and c-di-GMP phosphodiesterase YfgF in biofilm formation and H2O2 stress response in avian pathogenic Escherichia coli

Avian pathogenic Escherichia coli (APEC) is a widespread bacterial pathogen that poses a significant threat to the poultry industry globally. It is of great significance to control APEC infections by investigating the molecular mechanisms that regulate APEC's adaptation to new environments and its survival. APEC possesses a series of regulation systems to sense and quickly and appropriately respond to extracellular environmental changes, and causes the host infection. Two-component system (TCS) and second messenger (SM) are important regulation systems ubiquitous in APEC and play vital roles in regulating a variety of bacterial functions, such as biofilm formation, H2O2 stress response, and virulence. Among them, BasS/BasR is a typical TCS, and c-di-GMP is a widely utilized intracellular SM. The metabolism of c-di-GMP is inversely controlled by diguanylate cyclase (DGC) and phosphodiesterase (PDE). However, the connection between BasS/BasR and c-di-GMP in regulating the biological functions of APEC has not yet been clarified. This study aims to investigate the cross-regulation between BasS/BasR and YfgF in biofilm formation, H2O2 stress response, and APEC virulence, and to elucidate the underlying molecular mechanisms. In this study, we first demonstrated that BasS/BasR inhibits the transcription of yfgF (encoding a c-di-GMP phosphodiesterase YfgF) by directly binding to its promoter and resulted in increased intracellular c-di-GMP levels in response to extracellular signals. This, in turn, results in increased biofilm formation, promotes APEC adhesion, and reduces resistance to H2O2. Furthermore, BasS/BasR also directly facilitates biofilm formation, enhances APEC virulence, and increases sensitivity to H2O2 by specifically binding to the promoters of csgD, ais, fepA, and yciFE, respectively. Taken together, this study suggests that the cross-regulation between BasS/BasR and c-di-GMP plays important roles in controlling biofilm formation, H2O2 stress response, and APEC virulence, thereby providing valuable insights into bacterial pathogenicity.