title: Reduced aeration affects the expression of the NorB efflux pump of Staphylococcus aureus by posttranslational modification of MgrA.
abstract: We previously showed that at acid pH, the transcription of norB, encoding the NorB efflux pump, increases due to a reduction in the phosphorylation level of MgrA, which in turn leads to a reduction in bacterial killing by moxifloxacin, a substrate of the NorB efflux pump. In this study, we demonstrated that reduced oxygen levels did not affect the transcript levels of mgrA but modified the dimerization of the MgrA protein, which remained mostly in its monomeric form. Under reduced aeration, we also observed a 21.7-fold increase in the norB transcript levels after 60 min of growth that contributed to a 4-fold increase in the MICs of moxifloxacin and sparfloxacin for Staphylococcus aureus RN6390. The relative proportions of MgrA in monomeric and dimeric forms were altered by treatment with H(2)O(2), but incubation of purified MgrA with extracts of cells grown under reduced but not normal aeration prevented MgrA from being converted to its dimeric DNA-binding form. This modification was associated with cleavage of a fragment of the dimerization domain of MgrA without change in MgrA phosphorylation and an increase in transcript levels of genes encoding serine proteases in cells incubated at reduced aeration. Taken together, these data suggest that modification of MgrA by proteases underlies the reversal of its repression of norB and increased resistance to NorB substrates in response to reduced-aeration conditions, illustrating a third mechanism of posttranslational modification, in addition to oxidation and phosphorylation, that modulates the regulatory activities of MgrA.
authors.affiliation: Division of Infectious Diseases and Medical Services, Massachusetts General Hospital, and Harvard Medical School, Boston, MA, USA.
authors.forename: Que Chi
authors.initials: QC
authors.lastname: Truong-Bolduc
authors.forename: Liao Chun
authors.initials: LC
authors.lastname: Hsing
authors.forename: Regis
authors.initials: R
authors.lastname: Villet
authors.forename: Gilles R
authors.initials: GR
authors.lastname: Bolduc
authors.forename: Zoe
authors.initials: Z
authors.lastname: Estabrooks
authors.forename: G Florent
authors.initials: GF
authors.lastname: Taguezem
authors.forename: David C
authors.initials: DC
authors.lastname: Hooper
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D010088:Oxidoreductases / Q000235:genetics* / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D013203:Staphylococcal Infections / Q000382:microbiology*; D013211:Staphylococcus aureus / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D010088:Oxidoreductases; C034747:nitric-oxide reductase; D010100:Oxygen