More Than Gliding: Involvement of GldD and GldG in the Virulence of Flavobacterium psychrophilum.

David Pérez-Pascual,Fabienne Neulat-Ripoll,Celine Henry,Jose A Guijarro,Edwige Quillet,Jean F Bernardet,Esther Gómez,Brigitte Kerouault,Tatiana Rochat,Eric Duchaud

doi:10.3389/fmicb.2017.02168

Abstract

A fascinating characteristic of most members of the genus Flavobacterium is their ability to move over surfaces by gliding motility. Flavobacterium psychrophilum, an important pathogen of farmed salmonids worldwide, contains in its genome the 19 gld and spr genes shown to be required for gliding or spreading in Flavobacterium johnsoniae; however, their relative role in its lifestyle remains unknown. In order to address this issue, two spreading deficient mutants were produced as part of a Tn4351 mutant library in F. psychrophilum strain THCO2-90. The transposons were inserted in gldD and gldG genes. While the wild-type strain is proficient in adhesion, biofilm formation and displays strong proteolytic activity, both mutants lost these characteristics. Extracellular proteome comparisons revealed important modifications for both mutants, with a significant reduction of the amounts of proteins likely transported through the outer membrane by the Type IX secretion system, indicating that GldD and GldG proteins are required for an effective activity of this system. In addition, a significant decrease in virulence was observed using rainbow trout bath and injection infection models. Our results reveal additional roles of gldD and gldG genes that are likely of importance for the F. psychrophilum lifestyle, including virulence.

Highlights

Many members of the phylum Bacteroidetes show gliding motility, the movement of cells over surfaces without the aid of pili or flagella
E. coli strains were grown at 37◦C in Luria Bertani (LB) with 15 g of agar per liter added for solid medium
To develop a functional genomic approach aiming to understand the role and the relative importance of genes of F. psychrophilum, a Tn4351-mutant library was constructed in strain THCO2-90 according to the previously developed strategy (Álvarez et al, 2004)

Summary

Introduction

Many members of the phylum Bacteroidetes show gliding motility, the movement of cells over surfaces without the aid of pili or flagella. Gld Proteins Involvement in BCWD encode proteins with redundant motility functions (Hunnicutt et al, 2002; Braun and McBride, 2005; Braun et al, 2005; Liu et al, 2007; Nelson et al, 2007, 2008; Rhodes et al, 2011a,b; Shrivastava et al, 2012) Some of these genes (i.e., gldK, gldL, gldM, gldN, sprA, sprE, and sprT) are orthologs of porK, porL, porM, porN, sov, porW, and porT genes, respectively, encoding the core secretion machinery of the newly described Type IX secretion system (T9SS) identified in the non-gliding periodontal pathogen Porphyromonas gingivalis (Sato et al, 2010, 2013). This process appears to be driven by a proton-motive force-dependent trans-envelope motor (Nakane et al, 2013; McBride and Nakane, 2015; Shrivastava and Berg, 2015; Shrivastava et al, 2015)

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Conclusion