Cytotoxin- and Chemotaxis-Genes Cooperate to Promote Adhesion of Photobacterium damselae subsp. damselae.

Carlos R Osorio,Sabine Schmidt,Matthias Husmann,Ana Vences,Gisela Von Hoven,Martina Meyenburg,Claudia Neukirch,Amable J Rivas

doi:10.3389/fmicb.2018.02996

Abstract

Photobacterium damselae subsp. damselae (Pdd) is an emerging pathogen of marine animals that sometimes causes serious infections in humans. Two related pore forming toxins, phobalysins P and C, and damselysin, a phospholipase D, confer strong virulence of Pdd in mice. Because infections by Pdd are typically caused following exposure of wounds to sea water we investigated how salinity impacts toxin activity, swimming, and association of Pdd with epithelial cells. These activities were low when bacteria were pre-cultured in media with 3.5% NaCl, the global average salinity of sea water. In contrast, lower salinity increased swimming of wild type Pdd peaking at 2% NaCl, hemolysis, and association with epithelial cells peaking at 1–1.5%. Previously, we have found that hemolysin genes enhance the association of Pdd with epithelial cells, but the underlying mechanisms have remained ill-defined. We here searched for potential links between hemolysin-production, chemotaxis and association of Pdd with target cells at varying salt concentrations. Unexpectedly, disruption of chemotaxis regulator cheA not only affected bacterial swimming and association with epithelial cells at intermediate to low salinity, but also reduced the production of plasmid-encoded phobalysin (PhlyP). The results thus reveal unforeseen links between chemotaxis regulators, a pore forming toxin and the association of a marine bacterium with target cells.

Highlights

Photobacterium damselae subsp. damselae (Pdd), formerly Vibrio damsela, is a pathogen of marine animals (Rivas et al, 2013b; Osorio et al, 2018), which causes septicemia and hyper-aggressive necrotizing soft tissue infections in humans (Clarridge and Zighelboim-Daum, 1985; Yamane et al, 2004)
In order to verify that swimming of Pdd on soft-agar depends on its chemotactic ability, we studied a Pdd strain containing a disruption of its only cheA gene (AR263) (Rivas et al, 2015b)
The principal novelty of the present study is the discovery of a regulatory link between a bacterial cytolytic activity and the molecular chemotaxis machinery: disruption of cheA or treatment with phenamil, an inhibitor of the sodium channel of the flagellar motor, both reduced motility and production of phobalysin P (PhlyP)

Summary

Introduction

Photobacterium damselae subsp. damselae (Pdd), formerly Vibrio damsela, is a pathogen of marine animals (Rivas et al, 2013b; Osorio et al, 2018), which causes septicemia and hyper-aggressive necrotizing soft tissue infections in humans (Clarridge and Zighelboim-Daum, 1985; Yamane et al, 2004). Strains of particular virulence produce plasmid-encoded damselysin (Dly) and phobalysin P (PhlyP), a phospholipase D, and a small pore-forming toxin (PFT), respectively. All hemolytic strains express chromosomally encoded phobalysin C (PhlyC), which is closely related to PhlyP. Frontiers in Microbiology | www.frontiersin.org von Hoven et al. Cooperation of che and a Pore Forming Toxin a phospholipase (PlpV) appears to be expressed by all strains; and a collagenase (ColP) is found in a subpopulation of Pdd (Vences et al, 2017; Osorio et al, 2018). Bacterial adhesion to the host represents an important step to infection. A role of hemolysins for the association of Pdd (Rivas et al, 2015b) or other bacteria (Krawczyk-Balska and Bielecki, 2005; Lucas et al, 2010; Vadia et al, 2011; Seitz et al, 2013) with host cells has emerged.

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