Phase-variable outer membrane proteins in Escherichia coli

Owen, P

doi:10.1016/s0928-8244(96)00069-7

Cited by 53 publications

(92 citation statements)

References 15 publications

(26 reference statements)

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“…Most auto-aggregation studies performed thus far have found a uniform distribution of autotransporters such as Ag43 and AIDA-I (Benz & Schmidt, 1992;Henderson et al, 1997b;Owen et al, 1996;Sherlock et al, 2004). However, these studies were mainly done using laboratory E. coli K-12 strains.…”

Section: Discussionmentioning

confidence: 99%

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Cellular chain formation in Escherichia coli biofilms

Vejborg

Klemm

2009

Microbiology

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In this study we report on a novel structural phenotype in Escherichia coli biofilms: cellular chain formation. Biofilm chaining in E. coli K-12 was found to occur primarily by clonal expansion, but was not due to filamentous growth. Rather, chain formation was the result of intercellular interactions facilitated by antigen 43 (Ag43), a self-associating autotransporter (SAAT) protein, which has previously been implicated in auto-aggregation and biofilm formation. Immunofluorescence microscopy suggested that Ag43 was concentrated at or near the cell poles, although when the antigen was highly overexpressed, a much more uniform distribution was seen. Immunofluorescence microscopy also indicated that other parameters, including dimensional constraints (flow, growth alongside a surface), may also affect the final biofilm architecture. Moreover, chain formation was affected by other surface structures; type I fimbriae expression significantly reduced cellular chain formation, presumably by steric hindrance. Cellular chain formation did not appear to be specific to E. coli K-12. Although many urinary tract infection (UTI) isolates were found to form rather homogeneous, flat biofilms, three isolates, including the prototypic asymptomatic bacteriuria strain, 83972, formed highly elaborate cellular chains during biofilm growth in human urine. Combined, these results illustrate the diversity of biofilm architectures that can be observed even within a single microbial species. INTRODUCTIONMany bacteria live in highly complex sessile communities, referred to as biofilms (Costerton et al., 1978; Geesey et al., 1977). These compact microbial consortia often confer certain advantages on the microbial population, such as antibiotic resistance, immune evasion, shear resistance and general persistence in changing and often hostile environments (Costerton et al., 1995(Costerton et al., , 1999. As such, microbial biofilms constitute a significant problem in various industrial and food-related areas, where microbial colonization often imposes a considerable financial burden (Donlan & Costerton, 2002;Lee Wong, 1998). Microbial biofilm formation has also been implicated in the development and persistence of a range of both implantand non-implant-related infections (Costerton et al., 1999). This has warranted a greater understanding of the importance of microbial biofilms in both health and disease, and of biofilm formation in itself.Escherichia coli is a genetically diverse microbial species. While E. coli is usually associated with a commensal lifestyle in the gastrointestinal tract, some E. coli strains have acquired specific virulence attributes that enable them to adapt to and colonize distinct host niches. Pathogenic E. coli causes a range of intestinal infectious diseases, usually manifested by diarrhoeal and dysentery-like symptoms (Kaper et al., 2004). E. coli is also responsible for a range of extra-intestinal infections, including urinary tract infections (UTIs), septicaemia and neonatal meningitis (Kaper et al., 2004). Sev...

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Section: Discussionmentioning

confidence: 99%

“…4A). Most other studies so far have indicated that Ag43 is distributed uniformly on the cell surface (Henderson et al, 1997a;Owen et al, 1996). However, in the majority of these studies, Ag43 was overexpressed.…”

Section: Cellular Location Of Ag43mentioning

confidence: 93%

Cellular chain formation in Escherichia coli biofilms

Vejborg

Klemm

2009

Microbiology

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“…A survey of enteropathogenic and urinary tract infectious strains showed that 77 and 60 %, respectively, of these were capable of Ag43 expression (Owen et al, 1996). Moreover, many strains posses duplex or multiple copies of the gene, as seems to be the case in enteropathogenic and enterohaemorrhagic subtypes Roche et al, 2001;Torres & Kaper, 2002).…”

Section: Discussionmentioning

confidence: 99%

Antigen-43-mediated autoaggregation impairs motility in Escherichia coli

2006

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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,...

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“…Interestingly, it is expressed by many pathogenic strains. Thus, a survey of enteropathogenic and urinary tract infection E. coli strains showed that 77 and 60%, respectively, of these strains were capable of Ag43 expression (21). Although E. coli K-12 has only one copy of the flu gene, it appears that the situation for wild-type strains is more complex and that two or more copies are present in enteropathogenic E. coli strains and some enterohemorrhagic E. coli strains (22,28).…”

Section: Discussionmentioning

confidence: 99%