The two-component system, BasSR, is involved in the regulation of biofilm and virulence in avian pathogenic Escherichia coli.

Avian pathogenic Escherichia coli (APEC) is a subgroup of extra-intestinal pathogenic E. coli (ExPEC) strains that cause avian colibacillosis, resulting in significant economic losses to the poultry industry worldwide. It has been reported that a few two-component signal transduction systems (TCS) participate in the regulation of the virulence factors of APEC infection. In this study, a basSR-deficient mutant strain was constructed from its parent strain APECX40 (WT), and high-throughput sequencing (RNA-seq) was performed to analyse the transcriptional profile of WT and its mutant strain XY1. Results showed that the deletion of basSR down-regulated the transcript levels of a series of biofilm- and virulence-related genes. Results of biofilm formation assays and bird model experiments indicated that the deletion of basSR inhibited biofilm formation in vitro and decreased bacterial virulence and colonization in vivo. In addition, electrophoretic mobility shift assays confirmed that the BasR protein could bind to the promoter regions of several biofilm- and virulence-related genes, including ais, opgC and fepA. This study suggests that the BasSR TCS might be a global regulator in the pathogenesis of APEC infection. RESEARCH HIGHLIGHTS Transcriptional profiling showed that BasSR might be a global regulator in APEC. BasSR increases APEC pathogenicity in vivo. BasSR positively regulates biofilm- and the virulence-associated genes. BasSR can bind to the promoter regions of virulence-associated genes ais, opgC and fepA.