title: The Fatty Acid Regulator FadR Influences the Expression of the Virulence Cascade in the El Tor Biotype of Vibrio cholerae by Modulating the Levels of ToxT via Two Different Mechanisms.
abstract: FadR is a master regulator of fatty acid (FA) metabolism that coordinates the pathways of FA degradation and biosynthesis in enteric bacteria. We show here that a ΔfadRmutation in the El Tor biotype ofVibrio choleraeprevents the expression of the virulence cascade by influencing both the transcription and the posttranslational regulation of the master virulence regulator ToxT. FadR is a transcriptional regulator that represses the expression of genes involved in FA degradation, activates the expression of genes involved in unsaturated FA (UFA) biosynthesis, and also activates the expression of two operons involved in saturated FA (SFA) biosynthesis. Since FadR does not bind directly to thetoxTpromoter, we determined whether the regulation of any of its target genes indirectly influenced ToxT. This was accomplished by individually inserting a double point mutation into the FadR-binding site in the promoter of each target gene, thereby preventing their activation or repression. Although preventing FadR-mediated activation offabA, which encodes the enzyme that carries out the first step in UFA biosynthesis, did not significantly influence either the transcription or the translation of ToxT, it reduced its levels and prevented virulence gene expression. In the mutant strain unable to carry out FadR-mediated activation offabA, expressingfabAectopically restored the levels of ToxT and virulence gene expression. Taken together, the results presented here indicate thatV. choleraeFadR influences the virulence cascade in the El Tor biotype by modulating the levels of ToxT via two different mechanisms.IMPORTANCEFatty acids (FAs) play important roles in membrane lipid homeostasis and energy metabolism in all organisms. InVibrio cholerae, the causative agent of the acute intestinal disease cholera, they also influence virulence by binding into an N-terminal pocket of the master virulence regulator, ToxT, and modulating its activity. FadR is a transcription factor that coordinately controls the pathways of FA degradation and biosynthesis in enteric bacteria. This study identifies a new link between FA metabolism and virulence in the El Tor biotype by showing that FadR influences both the transcription and posttranslational regulation of the master virulence regulator ToxT by two distinct mechanisms.
authors.affiliation: Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA.
authors.forename: Gabriela
authors.initials: G
authors.lastname: Kovacikova
authors.affiliation: Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Lin
authors.affiliation: Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA.
authors.forename: Ronald K
authors.initials: RK
authors.lastname: Taylor
authors.affiliation: Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA karen.skorupski@dartmouth.edu.
authors.forename: Karen
authors.initials: K
authors.lastname: Skorupski
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D005227:Fatty Acids / Q000096:biosynthesis; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D009154:Mutation; D011485:Protein Binding; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014734:Vibrio cholerae / Q000145:classification / Q000378:metabolism* / Q000472:pathogenicity*; D014774:Virulence
chemical_list: D001426:Bacterial Proteins; C057119:FadR protein, Bacteria; D005227:Fatty Acids; D012097:Repressor Proteins; D014157:Transcription Factors; C075626:tcpN protein, Vibrio cholerae
keywords: FadR; ToxT; fatty acid; pathogenesis; virulence