Autoinducer-2 promotes adherence of Aeromonas veronii through facilitating the expression of MSHA type IV pili genes mediated by c-di-GMP

ABSTRACT Aeromonas veronii. a ubiquitous of zoonotic disease pathogen, depends on adhesion as the crucial way to colonize the gastrointestinal tract of humans and animals, which further causes severe gastrointestinal diseases and parenteral infections. However, the adherence mechanism of A. veronii has not been fully characterized. Therefore, we investigate the effect of autoinducer-2 (AI-2) on adherence of A. veronii through facilitating the expression of mannose-sensitive hemagglutinin (MSHA) type IV pili genes mediated by cyclic diguanosine monophosphate (c-di-GMP). The deficiency of AI-2 significantly lowered the adherence of A. veronii to erythrocytes and intestinal mucus, and the complement of AI-2 could increase its adherence ability. The deficiency of AI-2 only limited the formation of pili, instead of outer-membrane proteins and lipopolysaccharide, through reducing the expression levels of MSHA type IV pili genes due to the decline of c-di-GMP. The addition of guanosine triphosphate (GTP) could increase the content of c-di-GMP and the expression of MSHA type IV pili genes, and further promote adherence of A. veronii . Therefore, this study reveals, for the first time, adherence mediated by c-di-GMP with MshE as the c-di-GMP receptor is positively regulated by AI-2 in A. veronii , which increases the understanding of colonization strategy of pathogen and may facilitate control of A. veronii infection to host. IMPORTANCE Aeromonas veronii can adhere to host cells through different adherence factors including outer-membrane proteins (OMPs), lipopolysaccharide (LPS), and pili, but its adherence mechanisms are still unclear. Here, we evaluated the effect of autoinducer-2 (AI-2) on adherence of A. veronii and its regulation mechanism. After determination of the promotion effect of AI-2 on adherence, we investigated which adherence factor was regulated by AI-2, and the results show that AI-2 only limits the formation of pili. Among the four distinct pili systems, only the mannose-sensitive hemagglutinin (MSHA) type IV pili genes were significantly downregulated after deficiency of AI-2. MshE, an ATPase belonged to MSHA type IV pilin, was confirmed as c-di-GMP receptor, that can bind with c-di-GMP which is positively regulated by AI-2, and the increase of c-di-GMP can promote the expression of MSHA type IV pili genes and adherence of A. veronii . Therefore, this study confirms that c-di-GMP positively regulated by AI-2 binds with MshE, then increases the expression of MSHA pili genes, finally promoting adherence of A. veronii , suggesting a multilevel positive regulatory adhesion mechanism that is responsible for A. veronii adherence.