title: Role of BrnQ1 and BrnQ2 in branched-chain amino acid transport and virulence in Staphylococcus aureus.
abstract: The branched-chain amino acids (BCAAs; Ile, Leu, and Val) not only are important nutrients for the growth of Staphylococcus aureus but also are corepressors for CodY, which regulates virulence gene expression, implicating BCAAs as an important link between the metabolic state of the cell and virulence. BCAAs are either synthesized intracellularly or acquired from the environment. S. aureus encodes three putative BCAA transporters, designated BrnQ1, BrnQ2, and BrnQ3; their functions have not yet been formally tested. In this study, we mutated all three brnQ paralogs so as to characterize their substrate specificities and their roles in growth in vitro and in vivo. We demonstrated that in the community-associated, methicillin-resistant S. aureus (CA-MRSA) strain USA300, BrnQ1 is involved in uptake of all three BCAAs, BrnQ2 transports Ile, and BrnQ3 does not have a significant role in BCAA transport under the conditions tested. Of the three, only BrnQ1 is essential for USA300 to grow in a chemically defined medium that is limited for Leu or Val. Interestingly, we observed that a brnQ2 mutant grew better than USA300 in media limited for Leu and Val, owing to the fact that this mutation leads to overexpression of brnQ1. In a murine infection model, the brnQ1 mutant was attenuated, but in contrast, brnQ2 mutants had significantly increased virulence compared to that of USA300, a phenotype we suggest is at least partially linked to enhanced in vivo scavenging of Leu and Val through BrnQ1. These data uncover a hitherto-undiscovered connection between nutrient acquisition and virulence in CA-MRSA.
authors.affiliation: Department of Microbiology and Immunology, University of Western Ontario, London, Ontario, Canada.
authors.forename: Julienne C
authors.initials: JC
authors.lastname: Kaiser
authors.affiliation: Department of Microbiology and Immunology, University of Western Ontario, London, Ontario, Canada.
authors.forename: Sameha
authors.initials: S
authors.lastname: Omer
authors.affiliation: Department of Microbiology and Immunology, University of Western Ontario, London, Ontario, Canada.
authors.forename: Jessica R
authors.initials: JR
authors.lastname: Sheldon
authors.affiliation: Department of Animal Care and Veterinary Services, University of Western Ontario, London, Ontario, Canada.
authors.forename: Ian
authors.initials: I
authors.lastname: Welch
authors.affiliation: Department of Microbiology and Immunology, University of Western Ontario, London, Ontario, Canada Centre for Human Immunology, University of Western Ontario, London, Ontario, Canada deh@uwo.ca.
authors.forename: David E
authors.initials: DE
authors.lastname: Heinrichs
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D003470:Culture Media / Q000737:chemistry; D015964:Gene Expression Regulation, Bacterial; D006801:Humans; D007532:Isoleucine / Q000378:metabolism; D007668:Kidney / Q000382:microbiology / Q000473:pathology; D007700:Kinetics; D007930:Leucine / Q000378:metabolism; D008099:Liver / Q000382:microbiology / Q000473:pathology; D055624:Methicillin-Resistant Staphylococcus aureus / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity*; D051379:Mice; D008807:Mice, Inbred BALB C; D009154:Mutation; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D013203:Staphylococcal Infections / Q000382:microbiology* / Q000473:pathology; D013379:Substrate Specificity; D014633:Valine / Q000378:metabolism; D014774:Virulence
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; C540555:CodY protein, Staphylococcus aureus; D003470:Culture Media; D012097:Repressor Proteins; D007532:Isoleucine; D007930:Leucine; D014633:Valine