The regulation of AsfR on tmRNA expression mediates bacterial motility and virulence in Aeromonas veronii

Transfer messenger RNA (tmRNA), a key component of the trans-translation system, plays an essential role on the virulence of pathogenic bacteria. However, the upstream regulatory mechanisms that regulate tmRNA expression remain largely unexplored. In this study, AraC superfamily regulator (AsfR) was found to directly interact with the promoter of ssrA gene, which encodes tmRNA. Co-transformation of the reporter construct, consisting of tmRNA promoter fused to enhanced green fluorescent protein (eGFP), alongside an AsfR expression vector, resulted in increased fluorescence, indicating that AsfR positively regulates mRNA expression. Consistently, the transcription level of tmRNA was significantly decreased in ΔasfR compared with WT of A. veronii by quantitative real-time PCR (RT-qPCR) analyses. The ΔasfR and ΔtmRNA mutants exhibited significantly reduced motility and biofilm formation. Reduced transcription of the flagellar gene fliE in both mutants suggests that the AsfR/tmRNA axis may regulate these processes via fliE. Furthermore, deletion of asfR and tmRNA impairs oxidant resistance and pathogenicity, resulting in growth inhibition in A. veronii. This study elucidates the regulatory role of the AsfR-tmRNA pathway in flagellar motility, biofilm formation, and antioxidant capacity, all of which contribute to bacterial virulence and provide potential targets for the treatment of bacterial infections.