LitR Is a Repressor of syp Genes and Has a Temperature-Sensitive Regulatory Effect on Biofilm Formation and Colony Morphology in Vibrio (Aliivibrio) salmonicida

Abstract

c Vibrio (Aliivibrio) salmonicida is the etiological agent of cold water vibriosis, a disease in farmed Atlantic salmon (Salmo salar) that is kept under control due to an effective vaccine. A seawater temperature below 12°C is normally required for disease development. Quorum sensing (QS) is a cell density-regulated communication system that bacteria use to coordinate activities involved in colonization and pathogenesis, and we have previously shown that inactivation of the QS master regulator LitR attenuates the V. salmonicida strain LFI1238 in a fish model. We show here that strain LFI1238 and a panel of naturally occurring V. salmonicida strains are poor biofilm producers. Inactivation of litR in the LFI1238 strain enhances medium-and temperaturedependent adhesion, rugose colony morphology, and biofilm formation. Chemical treatment and electron microscopy of the biofilm identified an extracellular matrix consisting mainly of a fibrous network, proteins, and polysaccharides. Further, by microarray analysis of planktonic and biofilm cells, we identified a number of genes regulated by LitR and, among these, were homologues of the Vibrio fischeri symbiosis polysaccharide (syp) genes. The syp genes were regulated by LitR in both planktonic and biofilm lifestyle analyses. Disruption of syp genes in the V. salmonicida ⌬litR mutant alleviated adhesion, rugose colony morphology, and biofilm formation. Hence, LitR is a repressor of syp transcription that is necessary for expression of the phenotypes examined. The regulatory effect of LitR on colony morphology and biofilm formation is temperature sensitive and weak or absent at temperatures above the bacterium's upper threshold for pathogenicity.

Exploring the transcriptome of luxI- and ΔainS mutants and the impact of N-3-oxo-hexanoyl-L- and N-3-hydroxy-decanoyl-L-homoserine lactones on biofilm formation in Aliivibrio salmonicida

“…salmonicida (Hansen et al, 2014;Khider, Willassen & Hansen, 2018). Consistently, our RNA-Seq data at HCD demonstrated 11 significantly upregulated genes of the syp operon with fold change values ranging from 9.55 to 2.04.…”

“…The ability to form rugose colonies and biofilm are often correlated features in vibrios (Casper-Lindley & Yildiz, 2004;Yildiz & Schoolnik, 1999;Yildiz et al, 2004), where wrinkled colony phenotype is generally associated with enhanced exopolysaccharide production (Yildiz & Schoolnik, 1999). Likewise, in A. salmonicida colony wrinkling (rugosity) and biofilm formation requires the expression of syp genes responsible for the production of EPS (Hansen et al, 2014;Khider, Willassen & Hansen, 2018). In the study presented here we show that luxImutant exhibited a strong wrinkling colony morphology, indicating an enhanced polysaccharide production.…”

“…A mutation in the master regulator HapR, results in a state mimicking low cell density conditions, where the mutant produces more exopolysaccharides compared to wild-type (Zhu & Mekalanos, 2003). A. salmonicida behaves in a similar fashion to V. cholerae, where deletion of litR leads to increase exopolysaccharide production and formation of three-dimensional biofilm structure (Bjelland et al, 2012;Hansen et al, 2014).…”

Nonribosomal Peptide Synthase Gene Clusters for Lipopeptide Biosynthesis in Bacillus subtilis 916 and Their Phenotypic Functions

“…However, it seems that the fengycins contribute only to the antifungal activity and are not involved in other phenotypical features of B. subtilis 916. In view of the different contributions of surfactins, bacillomycin Ls, and locillomycins to multicellular behaviors of B. subtilis 916, it will be interesting to further decipher the detailed mechanisms of different LPs with regard to how they trigger active kinase expression and regulate the swarming motility, biofilm formation, and colony morphology of B. subtilis 916 (21,22,(34)(35)(36)(37)(38)(39).…”

Involvement of the Type IX Secretion System in Capnocytophaga ochracea Gliding Motility and Biofilm Formation

“…Enzymatic treatment was carried out as described previously, with minor modifications (39,40). Biofilms (produced by 100 l of bacterial culture) were grown for 48 h in the wells of 96-well polystyrene microtiter plates, as described for the crystal violet biofilm formation assay.…”