Expression of Vibrio vulnificus Capsular Polysaccharide Inhibits Biofilm Formation

Abstract

Vibrio vulnificus is a human pathogen that produces lethal septicemia in susceptible persons, and the primary virulence factor for this organism is capsular polysaccharide (CPS). The role of the capsule in V. vulnificus biofilms was examined under a variety of conditions, by using either defined CPS mutants or spontaneous CPS expression phase variants derived from multiple strains. CPS expression was shown to inhibit attachment and biofilm formation, which contrasted with other studies describing polysaccharides as integral to biofilms in related species.Vibrio vulnificus is indigenous to estuarine environments (9,18,24,36,43) and causes human infections associated with raw oyster consumption (3). Pathogenesis was recently reviewed, and virulence is primarily attributed to capsular polysaccharide (CPS) expression (34). Opaque (O) colony morphology, indicative of a virulent, encapsulated phenotype, exhibits reversible phase variation to translucent (T) colony types with reduced CPS expression and decreased virulence (30,47). Defined mutations in the CPS operon confirmed the relationship of CPS and virulence (28,42,44,45). Vibrio spp. attach to algae and zooplankton (5,15,16,17,19,22), and V. vulnificus may be more concentrated in oysters and fish which feed on these organisms (9,29,36,43). Microbial communities attached to nutrient-rich surfaces are generally referred to as biofilms and are thought to engage in complex signaling for expression of CPS and other factors (7,25,26). For example, V. cholerae biofilms require production of polysaccharide, pili, and flagella (5,21,23,37,38,39,46). Biofilms for V. vulnificus biotype 2 eel pathogens were recently described (20); however, this group differs from human pathogens of biotype 1 in that biotype 2 lipopolysaccharide (LPS) is homogeneous (serovar E) and CPS may not always be required for virulence (2). The role of CPS in biofilms of either biotype has not been addressed; therefore, our studies examined V. vulnificus biofilms in O versus T phase variants and CPS mutants that differed in their abilities to produce capsular polysaccharide.CPS expression inhibits V. vulnificus biofilm formation. Surface CPS displays a continuum of expression among V. vulnificus strains (44). Strains for this study are detailed in Table 1 and were stored at Ϫ70°C in 50% glycerol to ensure stability of phase variants. O strains are completely encapsulated, while T strains either are acapsular or have reduced, patchy capsules. Mutant strains are acapsular but differ in CPS biosynthesis: CVD752 contains a polar transposon mutation in the CPS operon that eliminates biosynthesis, while MO6-24/31T contains a nonpolar mutation, specifically targeting the CPS transport function of the wza gene, and can synthesize CPS but is unable to transport it to the cell surface (44, 45).Biofilm formation on abiotic surfaces was examined by crystal violet absorption assays, and the relative biofilm content was estimated from the concentration of dye eluted from destained cells and matrix (32). Examination...

Genetic determinants of biofilm development of opaque and translucent Vibrio parahaemolyticus

“…OP strains of V. vulnificus also produce a capsule, and this capsule is known to confer virulence (Yoshida et al, 1985;Simpson et al, 1987;Wright et al, 1999). These opacity-determining capsules of V. cholerae O-139 and V. vulnificus interfere with biofilm formation (Kierek and Watnick, 2003a,b;Joseph and Wright, 2004). V. cholerae strains (O139 as well as O1) also produce another form of extracellular polysaccharide, designated VPS.…”

Sticky Situations: Key Components That Control Bacterial Surface Attachment

“…appear to have negative roles. For example, loss of the group 1 capsular polysaccharide (CPS) in V. vulnificus is associated with increased attachment and, subsequently, reduced biofilm formation (23,73). V. cholerae O139 contains a locus with genes for CPS and lipopolysaccharide (LPS) O antigen biosynthesis that also plays a negative role in biofilm formation (77).…”

Identification of the Vibrio vulnificus wbpP Gene and Evaluation of Its Role in Virulence

“…When the autoagglutination activities of NY018 and the wild type were compared according to the procedures of Misawa and Blaser (22), the mutant was not as agglutinating as the wild type, indicating that the impaired adherence exhibited by the wbpP mutant might be related to its decreased autoagglutination activity (data not shown). However, it has recently been observed that the production of CPS and the ability of V. vulnificus to form a biofilm on abiotic surfaces are inversely related (12). This suggests that the correlation between CPS and V. vulnificus adhesion may vary with complex parameters that still remain to be determined.…”