The Tat system and its dependent cell division proteins are critical for virulence of extra-intestinal pathogenic Escherichia coli

The twin-arginine translocation (Tat) system is involved in a variety of important bacterial physiological processes. Conserved among bacteria and crucial for virulence, the Tat system is deemed as a promising anti-microbial drug target. However, the mechanism of how the Tat system functions in bacterial pathogenesis has not been fully understood. In this study, we showed that the Tat system was critical for the virulence of an extra-intestinal pathogenic E. coli (ExPEC) strain PCN033. A total of 20 Tat-related mutant strains were constructed, and competitive infection assays were performed to evaluate the relative virulence of these mutants. The results demonstrated that several Tat substrate mutants, including the ΔsufI, ΔamiAΔamiC double mutant as well as each single mutant, ΔyahJ, ΔcueO, and ΔnapG, were significantly outcompeted by the WT strain, among which the ΔsufI and ΔamiAΔamiC strains showed the lowest competitive index (CI) value. Results of individual mouse infection assay, in vitro cell adhesion assay, whole blood bactericidal assay, and serum bactericidal assay further confirmed the virulence attenuation phenotype of the ΔsufI and ΔamiAΔamiC strains. Moreover, the two mutants displayed chained morphology in the log phase resembling the Δtat and were defective in stress response. Our results suggest that the Tat system and its dependent cell division proteins SufI, AmiA, and AmiC play critical roles during ExPEC pathogenesis.双精氨酸转运（Twin-arginine translocation, Tat）系统参与多种重要的细菌生理过程。该系统在细菌中高度保守，且对致病菌的毒力至关重要，因此被视为极具潜力的抗微生物药物靶点。然而，Tat系统在细菌致病过程中的具体作用机制尚未完全阐明。本研究证实，Tat系统对肠外致病性大肠杆菌（extra-intestinal pathogenic E. coli, ExPEC）菌株PCN033的毒力具有关键作用。研究人员共构建了20株Tat相关突变菌株，并通过竞争性感染实验评估了各突变株的相对毒力。实验结果显示，包括ΔsufI、ΔamiAΔamiC双突变株及其各自单突变株、ΔyahJ、ΔcueO与ΔnapG在内的数株Tat底物蛋白突变株的增殖竞争力显著弱于野生型（WT）菌株；其中ΔsufI与ΔamiAΔamiC突变株的竞争指数（CI）值最低。小鼠单独感染实验、体外细胞黏附实验、全血杀菌实验及血清杀菌实验的结果进一步验证了ΔsufI与ΔamiAΔamiC突变株的毒力衰减表型。此外，这两株突变株在对数生长期呈现出与Δtat突变株相似的链状形态，且应激反应存在缺陷。本研究结果表明，Tat系统及其依赖的细胞分裂蛋白SufI、AmiA与AmiC在肠外致病性大肠杆菌的致病过程中发挥关键作用。