AUTHOR=Nguyen Minh-Thu , Saising Jongkon , Tribelli Paula Maria , Nega Mulugeta , Diene Seydina M. , François Patrice , Schrenzel Jacques , Spröer Cathrin , Bunk Boyke , Ebner Patrick , Hertlein Tobias , Kumari Nimerta , Härtner Thomas , Wistuba Dorothee , Voravuthikunchai Supayang P. , Mäder Ulrike , Ohlsen Knut , Götz Friedrich 

TITLE=Inactivation of farR Causes High Rhodomyrtone Resistance and Increased Pathogenicity in Staphylococcus aureus

JOURNAL=Frontiers in Microbiology

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2019.01157

DOI=10.3389/fmicb.2019.01157

ISSN=1664-302X

ABSTRACT=<p>Rhodomyrtone (Rom) is an acylphloroglucinol antibiotic originally isolated from leaves of <italic>Rhodomyrtus tomentosa</italic>. Rom targets the bacterial membrane and is active against a wide range of Gram-positive bacteria but the exact mode of action remains obscure. Here we isolated and characterized a spontaneous Rom-resistant mutant from the model strain <italic>Staphylococcus aureus</italic> HG001 (Rom<sup>R</sup>) to learn more about the resistance mechanism. We showed that Rom-resistance is based on a single point mutation in the coding region of <italic>farR</italic> [regulator of <underline>f</underline>atty <underline>a</underline>cid (FA) <underline>r</underline>esistance] that causes an amino acid change from Cys to Arg at position 116 in FarR, that affects FarR activity. Comparative transcriptome analysis revealed that mutated <italic>farR</italic> affects transcription of many genes in distinct pathways. FarR represses for example the expression of its own gene (<italic>farR</italic>), its flanking gene <italic>farE</italic> (effector of FA resistance), and other global regulators such as <italic>agr</italic> and <italic>sarA</italic>. All these genes were consequently upregulated in the Rom<sup>R</sup> clone. Particularly the upregulation of <italic>agr</italic> and <italic>sarA</italic> leads to increased expression of virulence genes rendering the Rom<sup>R</sup> clone more cytotoxic and more pathogenic in a mouse infection model. The Rom-resistance is largely due to the de-repression of <italic>farE</italic>. FarE is described as an efflux pump for linoleic and arachidonic acids. We observed an increased release of lipids in the Rom<sup>R</sup> clone compared to its parental strain HG001. If <italic>farE</italic> is deleted in the Rom<sup>R</sup> clone, or, if native <italic>farR</italic> is expressed in the Rom<sup>R</sup> strain, the corresponding strains become hypersensitive to Rom. Overall, we show here that the high Rom-resistance is mediated by overexpression of <italic>farE</italic> in the Rom<sup>R</sup> clone, that FarR is an important regulator, and that the point mutation in <italic>farR</italic> (Rom<sup>R</sup> clone) makes the clone hyper-virulent.</p>