title: The flagellar master operon flhDC is a pleiotropic regulator involved in motility and virulence of the fish pathogen Yersinia ruckeri.
abstract: OBJECTIVE
  To investigate the function of the master flagellar operon flhDC in the fish pathogen Yersinia ruckeri and compare the effect of a constructed flhD mutation to a naturally occurring fliR mutation causing loss-of-motility in emergent biotype 2 (BT2) strains.
  
  
  RESULTS
  Yersinia ruckeri flhD and fliR mutants were constructed in a motile strain. Both mutations caused loss-of-motility, ablation of flagellin synthesis and phospholipase secretion, similar to naturally occurring BT2 strains. Transcriptome analysis confirmed flhDC regulation of flagellar, chemotaxis and phospholipase loci as well as other genes of diverse function. The flhD mutation confers a competitive advantage within the fish host when compared with its parent strain, while this advantage was not seen with the naturally occurring fliR mutation.
  
  
  CONCLUSIONS
  An intact flhD is necessary for expression of the flagellar secretion system as well as other diverse loci, consistent with a role for flhD as a pleiotropic regulator. The maintenance of the flhD locus in Y. ruckeri strains suggests its importance for aspects of Y. ruckeri biology other than virulence, since the flhD mutation conferred a competitive advantage during experimental challenge of rainbow trout.
  
  
  CONCLUSIONS
  Yersinia ruckeri is the causative agent of enteric red mouth disease, an invasive septicaemia that affects farmed salmonid fish species. Disease outbreaks can cause severe economic losses in aquaculture. BT2 variants, which have independently emerged worldwide, are an increasing threat to farmed fish production. Knowledge of mechanisms involved in virulence, conserved functions and gene regulation among strains may be exploited for the development of novel disease control strategies to prevent pathogen growth or virulence phenotypes within aquaculture.
authors.affiliation: Agricultural Research Service/U.S. Department of Agriculture, National Center for Cool and Cold Water Aquaculture, Kearneysville, WV, USA.
authors.forename: A K S
authors.initials: AK
authors.lastname: Jozwick
authors.affiliation: Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT, USA.|Institute for Systems Genomics, University of Connecticut, Storrs, CT, USA.
authors.forename: J
authors.initials: J
authors.lastname: Graf
authors.affiliation: Agricultural Research Service/U.S. Department of Agriculture, National Center for Cool and Cold Water Aquaculture, Kearneysville, WV, USA.
authors.forename: T J
authors.initials: TJ
authors.lastname: Welch
mesh_terms: D000818:Animals; D017756:Aquaculture; D005393:Fish Diseases / Q000382:microbiology*; D005407:Flagella / Q000502:physiology; D005786:Gene Expression Regulation; D017686:Oncorhynchus mykiss / Q000382:microbiology; D009876:Operon / Q000502:physiology*; D059467:Transcriptome; D014774:Virulence; D015009:Yersinia Infections / Q000382:microbiology; D044124:Yersinia ruckeri / Q000472:pathogenicity*
keywords: 
  Yersinia ruckeri
  ; 
  flhDC
  ; Oncorhynchus mykiss (Walbaum); aquaculture; flagella regulation; rainbow trout; virulence