Antigen-43-mediated autoaggregation impairs motility in Escherichia coli

Abstract

Functional interaction between bacterial surface-displayed autoaggregation proteins such as antigen 43 (Ag43) of Escherichia coli and motility organelles such as flagella has not previously been described. Here, it has been demonstrated for the first time that Ag43-mediated aggregation can inhibit bacterial motility. Ag43 overexpression produces a dominant aggregation phenotype that overrides motility in the presence of low levels of flagella. In contrast, induction of an increased flagellation state prevents Ag43-mediated aggregation. This phenomenon was observed in naturally occurring subpopulations of E. coli as phase variants expressing and not expressing Ag43 revealed contrasting motility phenotypes. The effects were shown to be part of a general mechanism because other short adhesins capable of mediating autoaggregation (AIDA-I and TibA) also impaired motility. These novel insights into the function of bacterial autoaggregation proteins suggest that a balance between these two systems, i.e. autoaggregation and flagellation, influences motility. INTRODUCTIONThe ability of bacteria to colonize and cause infection is often linked to the expression of specific surface structures. Examples include fimbriae that mediate attachment, flagella that mediate motility, aggregation factors that mediate cell clumping, and a capsule, which provides protection against phagocytosis and host defences. Although the function of these surface structures is often antagonistic, very little is understood regarding the molecular interactions that contribute to their contrasting phenotypes.Antigen 43 (Ag43) is an autotransporter (AT) protein of Escherichia coli that promotes bacterial cell-to-cell aggregation (Diderichsen, 1980;Hasman et al., 1999;Henderson & Owen, 1999;Owen, 1983). It can be expressed on the E. coli cell surface in very high numbers (up to 50 000 copies per cell), resulting in a characteristic frizzy colony morphology (Hasman et al., 2000;Henderson & Owen, 1999;Owen, 1992). Ag43-mediated aggregation is a distinct phenotype that can be visualized macroscopically as flocculation and settling of cells in static liquid suspensions. The protein belongs to the AIDA group of AT proteins and exhibits a high degree of homology to several other members of the AT protein family, namely the AIDA-I adhesin involved in diffuse adherence of enteropathogenic E. coli and the TibA adhesin of enterotoxigenic E. coli (Sherlock et al., 2004(Sherlock et al., , 2005. Ag43 is cleaved into two subunits (a and b), each constituting roughly half of the protein. The b subunit is believed to be an outer-membrane pore-forming component through which Ag43 a gains access to the bacterial surface. The a subunit, on the other hand, remains attached to the bacterial cell surface via interactions with the b subunit (Henderson et al., 2004). The expression of Ag43 is phase-variable with switching rates of~10 23 per cell per generation due to the concerted actions of Dam methylase (positive regulation) and OxyR (negative regulation) (Henderson & Owen,...

Mutation of a Salmonella Serogroup-C1-Specific Gene Abrogates O7-Antigen Biosynthesis and Triggers NaCl-Dependent Motility Deficiency

“…Previous studies with Campylobacter jejuni have correlated the expression of flagella with auto-aggregation [39], [40]. In E. coli , the auto-aggregation mediated by aggregation protein Ag43 can interfere with motility in the presence of low levels of flagella [41]. Our results together with these reports show that auto-aggregation and motility are antagonistic phenotypes.…”

The role of DNA base excision repair in filamentation in Escherichia coli K-12 adhered to epithelial HEp-2 cells

“…It is known that mutation of the E. coli oxidative stress response regulator gene oxyR results in overexpression of an adhesin related to biofilm formation (Ag43). As a result, E. coli oxyR mutants display an increase in biofilm formation and autoaggregation in addition to a decrease in motility (Ulett et al 2006). Moreover, rpoS, another regulator gene involved in several stress responses, may affect cell adherence (Dong et al 2009).…”

Molecular Characterization of the Vacuolating Autotransporter Toxin in Uropathogenic Escherichia coli

“…SDS-PAGE and transfer of proteins to a polyvinylidene difluoride (PVDF) membrane for Western blot analysis were performed as previously described (78). Anti-Vat polyclonal antibodies were used as the primary antibody, and alkaline phosphatase-conjugated anti-rabbit antibodies (Sigma-Aldrich) were used as the secondary antibody.…”