Dawei Yang，Yongwu Yang，Pengfei Qiao，Fengwei Jiang，Xinyang Zhang，Zihui Zhao，Tao Cai，Ganwu Li，Wentong Cai

mBio. 2023 Feb 14;e0315222.doi: 10.1128/mbio.03152-22. Online ahead of print.

Abstract

Enterohemorrhagic Escherichia coli (EHEC) is a highly adaptive pathogen and has acquired diverse genetic elements, such as genomic islands and prophages, via horizontal gene transfer to promote fitness  in vivo . Two-component signaling systems (TCSs) allow bacteria to sense, respond to, and adapt to various environments. This study identified a putative two-component signaling system composed of the histidine kinase EDL5436 (renamed LmvK) and the response regulator EDL5428 (renamed LmvR) in EHEC.  lmvK  and  lmvR  along with  EDL5429  to  EDL5434  ( EDL5429 - 5434 ) between them constitute the OI167 genomic island and are highly associated with the EHEC pathotype.  EDL5429 - 5434  encode transporters and metabolic enzymes that contribute to growth on mannose and are directly upregulated by LmvK/LmvR in the presence of mannose, as revealed by quantitative PCR (qPCR) and DNase I footprint assays. Moreover, LmvR directly activates the expression of the type III secretion system in response to mannose and promotes the formation of attaching and effacing lesions on HeLa cells. Using human colonoid and mouse infection models, we show that  lmvK  and  lmvR  contributed greatly to adherence and microcolony (MC) formation  ex vivo  and colonization  in vivo . Finally, RNA sequencing and chromatin immunoprecipitation coupled with sequencing analyses identified additional direct targets of LmvR, most of which are involved in metabolism. Given that mannose is a mucus-derived sugar that induces virulence and is preferentially used by EHEC during infection, our data revealed a previously unknown mechanism by which EHEC recognizes the host metabolic landscape and regulates virulence expression accordingly. Our findings provide insights into how pathogenic bacteria evolve by acquiring genetic elements horizontally to adapt to host environments. IMPORTANCE The gastrointestinal tract represents a complex and challenging environment for enterohemorrhagic Escherichia coli (EHEC). However, EHEC is a highly adaptable pathogen, requiring only 10 to 100 CFUs to cause infection. This ability was achieved partially by acquiring mobile genetic elements, such as genomic islands, that promote overall fitness. Mannose is an intestinal mucus-derived sugar that stimulates virulence and is preferentially used by EHEC during infection. Here, we characterize the OI167 genomic island of EHEC, which encodes a novel two-component signaling system (TCS) and transporters and metabolic enzymes (EDL5429-5434) involved in mannose utilization. The TCS directly upregulates  EDL5429 - 5434  and genes encoding the type III secretion system in the presence of mannose. Moreover, the TCS contributes greatly to EHEC virulence  ex vivo  and  in vivo . Our data demonstrate an elegant example in which EHEC strains evolve by acquiring genetic elements horizontally to recognize the host metabolic landscape and regulate virulence expression accordingly, leading to successful infections.

Keywords: enterohemorrhagic Escherichia coli; mannose metabolism; pathogenesis; type III secretion system; virulence regulation.