The gut microbiota can significantly impact invading pathogens and the disease they cause; however, many of the mechanisms that dictate commensal-pathogen interactions remain unclear. Enterohemorrhagic Escherichia coli (EHEC) is a potentially lethal human intestinal pathogen that uses microbiota-derived molecules as cues to efficiently regulate virulence factor expression. Here, we investigate the interaction between EHEC and Enterococcus faecalis, a common human gut commensal, and show that E. faecalis affects both expression and activity of the EHEC type III secretion system (T3SS) via two distinct mechanisms. First, in the presence of E. faecalis there is increased transcription of genes encoding the EHEC T3SS. This leads to increased effector translocation and ultimately greater numbers of pedestals formed on host cells. The same effect was observed with several strains of enterococci, suggesting that it is a general characteristic of this group. In a mechanism separate from E. faecalis-induced transcription of the T3SS, we report that an E. faecalis-secreted protease, GelE, cleaves a critical structural component of the EHEC T3SS, EspB. Our data suggest that this cleavage actually increases effector translocation by the T3SS, supporting a model where EspB proteolysis promotes maximum T3SS activity. Finally, we report that treatment of EHEC with E. faecalis-conditioned cell-free medium is insufficient to induce increased T3SS expression, suggesting that this effect relies on cell contact between E. faecalis and EHEC. This work demonstrates a complex interaction between a human commensal and pathogen that impacts both expression and function of a critical virulence factor.IMPORTANCE This work reveals a complex and multifaceted interaction between a human gut commensal, Enterococcus faecalis, and a pathogen, enterohemorrhagic E. coli We demonstrate that E. faecalis enhances expression of the enterohemorrhagic E. coli type III secretion system and that this effect likely depends on cell contact between the commensal and the pathogen. Additionally, the GelE protease secreted by E. faecalis cleaves a critical structural component of the EHEC type III secretion system. In agreement with previous studies, we find that this cleavage actually increases effector protein delivery into host cells by the secretion system. This work demonstrates that commensal bacteria can significantly shape expression and activity of pathogen virulence factors, which may ultimately shape the progression of disease.

中文翻译：

---

粪肠球菌增强肠出血性大肠杆菌 III 型分泌系统的表达和活性。

肠道微生物群可以显着影响入侵的病原体及其引起的疾病；然而，许多决定共生-病原体相互作用的机制仍不清楚。肠出血性大肠杆菌 (EHEC) 是一种潜在致命的人类肠道病原体，它使用微生物群衍生的分子作为有效调节毒力因子表达的线索。在这里，我们研究了 EHEC 和粪肠球菌（一种常见的人类肠道共生菌）之间的相互作用，并表明粪肠球菌通过两种不同的机制影响 EHEC III 型分泌系统 (T3SS) 的表达和活性。首先，在粪肠球菌存在的情况下，编码 EHEC T3SS 的基因转录增加。这导致效应子易位增加，并最终在宿主细胞上形成更多数量的基座。在几种肠球菌菌株中观察到相同的效果，表明这是该组的一般特征。在与粪肠球菌诱导的 T3SS 转录不同的机制中，我们报告了粪肠球菌分泌的蛋白酶 GelE 可切割肠出血性大肠杆菌 T3SS 的关键结构成分 EspB。我们的数据表明，这种切割实际上增加了 T3SS 的效应子易位，支持 EspB 蛋白水解促进最大 T3SS 活性的模型。最后，我们报告用粪肠球菌条件无细胞培养基处理 EHEC 不足以诱导 T3SS 表达增加，表明这种效应依赖于粪肠球菌和肠出血性大肠杆菌之间的细胞接触。这项工作证明了人类共生菌和病原体之间复杂的相互作用会影响关键毒力因子的表达和功能。重要意义这项工作揭示了人类肠道共生菌粪肠球菌和病原体肠出血性大肠杆菌之间复杂和多方面的相互作用我们证明粪肠球菌可增强肠出血性大肠杆菌 III 型分泌系统的表达，并且这种作用可能取决于共生体和病原体之间的细胞接触。此外，粪肠球菌分泌的 GelE 蛋白酶可裂解 EHEC III 型分泌系统的关键结构成分。与之前的研究一致，我们发现这种切割实际上增加了分泌系统将效应蛋白输送到宿主细胞中。