SmpB and tmRNA Orchestrate Purine Pathway for the Trimethoprim Resistance in Aeromonas veronii

Small protein B(SmpB) cooperates with transfer-messenger RNA (tmRNA) for trans-translation to ensure the quality control of protein synthesis in prokaryotes. Furthermore, they regulate cell metabolism separately. According to research, SmpB functions as a transcription factor, and tmRNA acts as a small RNA. Purine pathway has been reported to be related to trimethoprim resistance, including hypoxanthine synthesis, adenosine metabolism and guanosine metabolism. Another reason of drug tolerance is the efflux pump of the bacterium. In transcriptomic data, it was shown that the expression of some related enzymes in adenosine metabolism were raised significantly in smpB deletion strain than that of wild type, which led to the differential trimethoprim resistance of Aeromonas veronii (A. veronii). Furthermore, the metabolic products of adenosine AMP, cAMP, and deoxyadenosine were accumulated significantly. However, the expressions of the enzymes related to hypoxanthine synthesis and guanosine metabolism were elevated significantly in ssrA (small stable RNA, tmRNA) deletion strain, which eventually caused an augmented metabolic product xanthine. In addition, the deletion of ssrA also affected the significant downregulations of efflux pump acrA/acrB. The minimal inhibitory concentrations (MIC) were overall decreased after the trimethoprim treatment to the wild type, ΔsmpB and ΔssrA. And the difference in sensitivity between ΔsmpB and ΔssrA was evident. The MIC of ΔsmpB was descended significantly than those of wild type and ΔssrA in M9 medium supplemented with 1 mM adenosine, illustrating that the adenosine metabolism pathway was principally influenced by SmpB. Likewise, the strain ΔssrA conferred more sensitivity than wild type and ΔsmpB in M9 medium supplemented with 1mM guanosine. By overexpressing acrA/acrB, the tolerance to trimethoprim was partially recovered in ΔssrA. These results revealed that SmpB and tmRNA acted on different branches in purine metabolism, conferring the diverse trimethoprim resistance to A. veronii. This study suggests that the trans-translation system might be an effective target in clinical treatment of A. veronii and other multi-antibiotic resistance bacteria with trimethoprim.