Are type IV pili involved in <i>Vibrio anguillarum</i> virulence towards sea bass (<i>Dicentrarchus labrax</i> L.) larvae?

Abstract

Vibrio anguillarum, an important bacterial fish pathogen, expresses a variety of virulence factors contributing to its ability to cause vibriosis in fish. Many virulence factors of this pathogen remain however unknown. For example, a type IV pilus system was previously reported to be potentially involved in the virulence of this bacterium but no experimental evidence was reported yet. In this study, complete genome sequencing of V. anguillarum strain VIB15, shown to be highly virulent towards sea bass (Dicentrarchus labrax L.) larvae, revealed the presence of a PilA pilin. A V. anguillarum VIB15 pilA mutant was constructed and the pathogenicity of this mutant was assessed in a gnotobiotic sea bass system developed for virulence screening. Our results suggest that the V. anguillarum pilA gene is not crucial for virulence towards sea bass larvae. Possibly, another type IV pilus system identified in V. anguillarum, showing homology to the mannose-sensitive hemagglutinin pilin of Vibrio cholerae, may complement the pilA mutation. Alternatively, the type IV pilus system has a role in infection of juvenile or adult fish, rather than in the larval phase. As such, further research is required to unravel the potential role of type IV pili in V. anguillarum virulence.

A comprehensive review of Vibrio (Listonella) anguillarum: ecology, pathology and prevention

“…) which have been investigated for their role in host adhesion and virulence (Frans et al . ), data which remain inconclusive at the present time, in terms of virulence contribution.…”

“…Adhesion occurs more frequently within the mucus of fish intestines as opposed to surface skin cells (Chabrill on et al 2004) as the intestinal lining of fish is rich in glycosphingolipidscritical components of endocytotic functions in fish digestion (Jennemann et al 2012)upon which the pathogen is able to utilize as a key attachment site for colonization (Chisada et al 2013). Research suggests that V. anguillarum adhesion to host cells is facilitated using afimbrial means (Wang & Leung 2000), but the pathogen inherently holds the capability to assemble type IV pili (Rodkhum et al 2006) which have been investigated for their role in host adhesion and virulence (Frans et al 2013a), data which remain inconclusive at the present time, in terms of virulence contribution.…”

Comparative genome sequencing to assess the genetic diversity and virulence attributes of 15 Vibrio anguillarum isolates

“…To unequivocally demonstrate the role of these putative pathogenicity‐related genes in virulence, in vivo examination of their functional role should be performed using a knockout mutant as described for, for example, the pilA gene in Frans et al . (). It is clear that further research is necessary to elucidate the underlying mechanisms of virulence differences in V. anguillarum , for instance, using RNA sequencing (Sorek & Cossart ), epigenetics research (Gómez‐Díaz et al .…”

“…The VIB15 vir plasmid harboured three additional SNPs/InDels, but it appears that the regions containing these mutations are not crucial for virulence towards sea bass larvae, as demonstrated previously (Frans et al . ,b).…”