The alternative sigma factor RpoQ regulates colony morphology, biofilm formation and motility in the fish pathogen Aliivibrio salmonicida

Abstract

BackgroundQuorum sensing (QS) is a cell-to cell communication system that bacteria use to synchronize activities as a group. LitR, the master regulator of QS in Aliivibrio salmonicida, was recently shown to regulate activities such as motility, rugosity and biofilm formation in a temperature dependent manner. LitR was also found to be a positive regulator of rpoQ. RpoQ is an alternative sigma factor belonging to the sigma −70 family. Alternative sigma factors direct gene transcription in response to environmental signals. In this work we have studied the role of RpoQ in biofilm formation, colony morphology and motility of A. salmonicida LFI1238.ResultsThe rpoQ gene in A. salmonicida LFI1238 was deleted using allelic exchange. We found that RpoQ is a strong repressor of rugose colony morphology and biofilm formation, and that it controls motility of the bacteria. We also show that overexpression of rpoQ in a ΔlitR mutant of A. salmonicida disrupts the biofilm produced by the ΔlitR mutant and decreases its motility, whereas rpoQ overexpression in the wild-type completely eliminates the motility.ConclusionThe present work demonstrates that the RpoQ sigma factor is a novel regulatory component involved in modulating motility, colony morphology and biofilm formation in the fish pathogen A. salmonicida. The findings also confirm that RpoQ functions downstream of the QS master regulator LitR. However further studies are needed to elucidate how LitR and RpoQ work together in controlling phenotypes related to QS in A. salmonicida.Electronic supplementary materialThe online version of this article (10.1186/s12866-018-1258-9) contains supplementary material, which is available to authorized users.

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.…”

“…salmonicida (Khider, Willassen & Hansen, 2018). Earlier studies demonstrated that inactivation of the AHL synthase (e.g luxI homologous) in several bacteria caused a reduction in both AHL and EPS production (Koutsoudis et al, 2006;Molina et al, 2005;Von Bodman, Bauer & Coplin, 2003).…”

“…ΔainSluxI -, completely inhibited biofilm formation. We have previously shown that the disruption of either EPS or other matrix components (e.g proteins, lipoproteins and eDNA), disrupts the mature biofilm formation in A. salmonicida (Hansen et al, 2014;Khider, Willassen & Hansen, 2018). While ΔainS mutant did not produce neither mature biofilm nor wrinkled colonies, introduction of luxI mutation into ΔainS, resulted in strains (ΔainSluxI -) with threedimensional biofilm architecture and wrinkled colonies.…”

“…The colony morphology assay was carried mainly as described before (Hansen et al, 2014;Khider, Willassen & Hansen, 2018). From each secondary overnight culture, a 250 μl was harvested by centrifugation, and the pellet was re-suspended in 250 μl SWT.…”