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RpoS and indole signaling control the virulence of Vibrio anguillarum towards gnotobiotic sea bass (Dicentrarchus labrax) larvae.

Li X, Yang Q, Dierckens K, Milton DL, Defoirdt T - PLoS ONE (2014)

Bottom Line: Deletion of rpoS resulted in increased expression of the indole biosynthesis gene tnaA and in increased production of indole.Both rpoS deletion and the addition of exogenous indole (50-100 µM) resulted in decreased biofilm formation, exopolysaccharide production (a phenotype that is required for pathogenicity) and expression of the exopolysaccharide synthesis gene wbfD.Finally, in addition to the phenotypes found to be affected by indole, the rpoS deletion mutant also showed increased motility and decreased sensitivity to oxidative stress.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Aquaculture and Artemia Reference Center, Ghent University, Ghent, Belgium.

ABSTRACT
Quorum sensing, bacterial cell-to-cell communication with small signal molecules, controls the virulence of many pathogens. In contrast to other vibrios, neither the VanI/VanR acylhomoserine lactone quorum sensing system, nor the three-channel quorum sensing system affects virulence of the economically important aquatic pathogen Vibrio anguillarum. Indole is another molecule that recently gained attention as a putative signal molecule. The data presented in this study indicate that indole signaling and the alternative sigma factor RpoS have a significant impact on the virulence of V. anguillarum. Deletion of rpoS resulted in increased expression of the indole biosynthesis gene tnaA and in increased production of indole. Both rpoS deletion and the addition of exogenous indole (50-100 µM) resulted in decreased biofilm formation, exopolysaccharide production (a phenotype that is required for pathogenicity) and expression of the exopolysaccharide synthesis gene wbfD. Further, indole inhibitors increased the virulence of the rpoS deletion mutant, suggesting that indole acts downstream of RpoS. Finally, in addition to the phenotypes found to be affected by indole, the rpoS deletion mutant also showed increased motility and decreased sensitivity to oxidative stress.

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Impact of RpoS on stress sensitivity of V. anguillarum.Survival of V. anguillarum wild type (WT) and rpoS deletion mutant (ΔrpoS) after 6 h incubation in sea water, with or without pyrogallol (10 mg l−1), and with or without catalase (10 mg l−1). Survival was determined by plate counting on LB20 agar. Error bars represent the standard error of three independent experiments. ** denotes a significant difference in survival of ΔrpoS when compared to WT (independent samples t-test; P<0.01).
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pone-0111801-g004: Impact of RpoS on stress sensitivity of V. anguillarum.Survival of V. anguillarum wild type (WT) and rpoS deletion mutant (ΔrpoS) after 6 h incubation in sea water, with or without pyrogallol (10 mg l−1), and with or without catalase (10 mg l−1). Survival was determined by plate counting on LB20 agar. Error bars represent the standard error of three independent experiments. ** denotes a significant difference in survival of ΔrpoS when compared to WT (independent samples t-test; P<0.01).

Mentions: RpoS has been reported to affect stress sensitivity in many bacteria, including V. anguillarum[20]. Therefore, we tested the impact of RpoS and indole on the resistance of V. anguillarum to reactive oxygen, which is part of the defense system of vertebrates and invertebrates. We have previously reported that the polyphenol compound pyrogallol inactivates vibrios by releasing peroxide, and that peroxide is neutralised by the addition of catalase [21]. Therefore, to assess resistance to oxidative stress, we exposed V. anguillarum to pyrogallol, with and without catalase. We found that the addition of pyrogallol resulted in>70% reduction of cell counts in wild-type V. anguillarum and that catalase could neutralise this effect (Figure 4). The rpoS deletion mutant was more sensitive than the wild-type, with approximately 90% reduction in cell counts. Again, the effect of pyrogallol could be neutralized by the addition of catalase. Finally, the addition of 100 µM indole did not affect resistance to oxidative stress of wild-type V. anguillarum (data not shown).


RpoS and indole signaling control the virulence of Vibrio anguillarum towards gnotobiotic sea bass (Dicentrarchus labrax) larvae.

Li X, Yang Q, Dierckens K, Milton DL, Defoirdt T - PLoS ONE (2014)

Impact of RpoS on stress sensitivity of V. anguillarum.Survival of V. anguillarum wild type (WT) and rpoS deletion mutant (ΔrpoS) after 6 h incubation in sea water, with or without pyrogallol (10 mg l−1), and with or without catalase (10 mg l−1). Survival was determined by plate counting on LB20 agar. Error bars represent the standard error of three independent experiments. ** denotes a significant difference in survival of ΔrpoS when compared to WT (independent samples t-test; P<0.01).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4216140&req=5

pone-0111801-g004: Impact of RpoS on stress sensitivity of V. anguillarum.Survival of V. anguillarum wild type (WT) and rpoS deletion mutant (ΔrpoS) after 6 h incubation in sea water, with or without pyrogallol (10 mg l−1), and with or without catalase (10 mg l−1). Survival was determined by plate counting on LB20 agar. Error bars represent the standard error of three independent experiments. ** denotes a significant difference in survival of ΔrpoS when compared to WT (independent samples t-test; P<0.01).
Mentions: RpoS has been reported to affect stress sensitivity in many bacteria, including V. anguillarum[20]. Therefore, we tested the impact of RpoS and indole on the resistance of V. anguillarum to reactive oxygen, which is part of the defense system of vertebrates and invertebrates. We have previously reported that the polyphenol compound pyrogallol inactivates vibrios by releasing peroxide, and that peroxide is neutralised by the addition of catalase [21]. Therefore, to assess resistance to oxidative stress, we exposed V. anguillarum to pyrogallol, with and without catalase. We found that the addition of pyrogallol resulted in>70% reduction of cell counts in wild-type V. anguillarum and that catalase could neutralise this effect (Figure 4). The rpoS deletion mutant was more sensitive than the wild-type, with approximately 90% reduction in cell counts. Again, the effect of pyrogallol could be neutralized by the addition of catalase. Finally, the addition of 100 µM indole did not affect resistance to oxidative stress of wild-type V. anguillarum (data not shown).

Bottom Line: Deletion of rpoS resulted in increased expression of the indole biosynthesis gene tnaA and in increased production of indole.Both rpoS deletion and the addition of exogenous indole (50-100 µM) resulted in decreased biofilm formation, exopolysaccharide production (a phenotype that is required for pathogenicity) and expression of the exopolysaccharide synthesis gene wbfD.Finally, in addition to the phenotypes found to be affected by indole, the rpoS deletion mutant also showed increased motility and decreased sensitivity to oxidative stress.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Aquaculture and Artemia Reference Center, Ghent University, Ghent, Belgium.

ABSTRACT
Quorum sensing, bacterial cell-to-cell communication with small signal molecules, controls the virulence of many pathogens. In contrast to other vibrios, neither the VanI/VanR acylhomoserine lactone quorum sensing system, nor the three-channel quorum sensing system affects virulence of the economically important aquatic pathogen Vibrio anguillarum. Indole is another molecule that recently gained attention as a putative signal molecule. The data presented in this study indicate that indole signaling and the alternative sigma factor RpoS have a significant impact on the virulence of V. anguillarum. Deletion of rpoS resulted in increased expression of the indole biosynthesis gene tnaA and in increased production of indole. Both rpoS deletion and the addition of exogenous indole (50-100 µM) resulted in decreased biofilm formation, exopolysaccharide production (a phenotype that is required for pathogenicity) and expression of the exopolysaccharide synthesis gene wbfD. Further, indole inhibitors increased the virulence of the rpoS deletion mutant, suggesting that indole acts downstream of RpoS. Finally, in addition to the phenotypes found to be affected by indole, the rpoS deletion mutant also showed increased motility and decreased sensitivity to oxidative stress.

Show MeSH