Abstract
Vibrio vulnificus is autochthonous to estuaries and warm coastal waters. Infection occurs via open wounds or ingestion, where its asymptomatic colonization of seafood, most infamously oysters, provides a gateway into the human food chain. Colonization begins with initial surface contact, which is often mediated by bacterial surface appendages called pili. Type IV Tad pili are widely distributed in the Vibrionaceae, but evidence for a physiological role for these structures is scant. The V. vulnificus genome codes for three distinct tad loci. Recently, a positive correlation was demonstrated between the expression of tad-3 and the phenotypes of a V. vulnificus descendent (NT) that exhibited increased biofilm formation, auto-aggregation, and oyster colonization relative to its parent. However, the mechanism by which tad pilus expression promoted these phenotypes was not determined. Here, we show that deletion of the tad pilin gene (flp) altered the near-surface motility profile of NT cells from high curvature, orbital retracing patterns characteristic of cells actively probing the surface to low curvature traces indicative of wandering and diminished bacteria–surface interactions. The NT flp pilin mutant also exhibited decreased initial surface attachment, attenuated auto-aggregation and formed fragile biofilms that disintegrated under hydrodynamic flow. Thus, the tad-3 locus, designated iam, promoted initial surface attachment, auto-aggregation and resistance to mechanical clearance of V. vulnificus biofilms. The prevalence of tad loci in the Vibrionaceae suggests that they may play equally important roles in other family members.
Highlights
Biofilms provide a protective environment for growth and, in nature, the majority of microorganisms live within complex biofilm communities.[1]
The tad locus was first reported as being required for biofilm formation by the oral pathogen, Actinobacillus actinomycetemcomitans and homologous loci were subsequently identified in several other pathogens.[8]
Homologs of the tad locus are widely distributed in the Vibrionaceae and many Vibrio genomes encoded multiple tad loci;[8,23] a physiological function had not be described for a Tad pilus for any family member
Summary
Biofilms provide a protective environment for growth and, in nature, the majority of microorganisms live within complex biofilm communities.[1]. Chitin-regulated competence (ChiRP) pili to attach to abiotic and chitinous surfaces, respectively.[14,15] The B-type toxin coregulated pilus is essential for intestinal colonization and pathogenesis.[16] The MSHA and ChiRP pili have been shown to play similar roles in V. parahaemolyticus,[17,18] a major cause of gastroenteritis, and V. vulnificus,[19,20,21] which has the highest death rate (>35%) and economic burden per case (>$3,000,000) of any foodborne pathogen in the United States.[22] Homologs of the tad locus are widely distributed in the Vibrionaceae and many Vibrio genomes encoded multiple tad loci;[8,23] a physiological function had not be described for a Tad pilus for any family member. We show that its expression promoted initial bacterial surface attachment and auto-aggregation, and increased the resistance of V. vulnificus biofilms to mechanical clearance—phenotypes associated with efficient niche (oyster) colonization.[20,23,24]
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