The inverse autotransporters of Yersinia ruckeri, YrInv and YrIlm, contribute to biofilm formation and virulence

Agnieszka Wrobel,Athanasios Saragliadis,Jesús Arenas,Krystyna Liskiewicz,Stephan Göttig,Maria Helle Spence,Jack C Leo,Kenneth Schneider,Jesús Pérez‐Ortega,Carolin Sittman,Dirk Linke

doi:10.1111/1462-2920.15051

Abstract

Yersinia ruckeri causes enteric redmouth disease (ERM) that mainly affects salmonid fishes and leads to significant economic losses in the aquaculture industry. An increasing number of outbreaks and the lack of effective vaccines against some serotypes necessitates novel measures to control ERM. Importantly, Y. ruckeri survives in the environment for long periods, presumably by forming biofilms. How the pathogen forms biofilms and which molecular factors are involved in this process, remains unclear. Yersinia ruckeri produces two surface-exposed adhesins, belonging to the inverse autotransporters (IATs), called Y. ruckeri invasin (YrInv) and Y. ruckeri invasin-like molecule (YrIlm). Here, we investigated whether YrInv and YrIlm play a role in biofilm formation and virulence. Functional assays revealed that YrInv and YrIlm promote biofilm formation on different abiotic substrates. Confocal microscopy revealed that they are involved in microcolony interaction and formation, respectively. The effect of both IATs on biofilm formation correlated with the presence of different biopolymers in the biofilm matrix, including extracellular DNA, RNA and proteins. Moreover, YrInv and YrIlm contributed to virulence in the Galleria mellonella infection model. Taken together, we propose that both IATs are possible targets for the development of novel diagnostic and preventative strategies to control ERM.

Highlights

Yersinia ruckeri is a Gram-negative bacterium and the causative agent of enteric redmouth disease (ERM) (Ross et al, 1966; Rucker, 1966; Kumar et al, 2015; Wrobel et al, 2019)
We investigated whether Y. ruckeri invasin (YrInv) and Y. ruckeri invasin-like molecule (YrIlm) play a role in biofilm formation and virulence
Functional assays revealed that YrInv and YrIlm promote biofilm formation on different abiotic substrates

Summary

Introduction

Yersinia ruckeri is a Gram-negative bacterium and the causative agent of enteric redmouth disease (ERM) (Ross et al, 1966; Rucker, 1966; Kumar et al, 2015; Wrobel et al, 2019). Yersinia ruckeri strains can be differentiated based on their biotypes (biotype 1 and biotype 2), serotypes (O1a; O2a, b, c; O3 and O4) and outer membrane protein profiles. Strains of serotype O1 are the major cause of ERM, referred to as yersiniosis. ERM affects wild fish and fish culture, in particular rainbow trout and Atlantic salmon. Vaccination and antibiotic treatment are the current strategies used to control the disease; the number of outbreaks, in Atlantic salmon, has substantially increased worldwide in recent years (Hjeltnes et al, 2017), suggesting that the pathogen is adapting to acquired host immune responses and antimicrobial treatments. ERM is considered as an emerging infectious disease, and there is an urgent need for novel control measures

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