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A new form of Staphylococcus aureus dormancy controlled by branched-chain amino acid availability in human macrophages

ABSTRACT: Staphylococcus aureus is a human commensal bacterium and opportunistic pathogen. Chronicity of S. aureus infection has been linked to bacterial survival within host cells including macrophages. Bacteria recovered from the intracellular milieu often form small colony variants (SCV) which are growing slowly, show reduced virulence factor production and are more resistant to antibiotics. Branched chain amino acids (BCAA) are an important class of nutrients for S. aureus. We therefore tested if components of BCAA biosynthesis or transport would alter the outcome of macrophage infection. We found that S. aureus mutants in the BCAA transporter BrnQ1 survived experimental infection of primary human macrophages for the complete duration of the 28 day experiments. Since phenotypic differences between brnQ1 mutants and wild-type bacteria occurred around 10 h p.i., we performed dual RNA-seq by which we determined the transcriptomes of both, pathogen and macrophage host, simultaneously. Our data indicate that at that time transcriptomic changes exclusively are governed by the internalized pathogen. The differential analysis of S. aureus WT and its isogenic brnQ1 mutant surprisingly demonstrated a dysregulation of iron-dependently regulated genes.

ORGANISM(S): Homo sapiens Staphylococcus aureus

PROVIDER: GSE235929 | GEO | 2023/06/28

REPOSITORIES: GEO

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Project description:We have observed that for a number of S. aureus strains as they switch to a SCV lifestyle there is the formation of an extracellular matrix. We focused our analysis on one strain, WCH-SK2. For bacterial survival in the host, the combination of low nutrients and the prolonged timeframe forms a stress that selects for a specific cell-type from the population. In this context, we used steady-state growth conditions with low nutrients and a controlled low growth rate, for a prolonged time and with methylglyoxal. These conditions induced S. aureus WCH-SK2 into a stable SCV cell-type, they did not revert after sub-culturing. Methods: Transcriptomic profiles of wild-type (WT) and SCV were generated in continuous culture in the presence of stress (high and low level of methylglyoxal). Results: Analysis revealed these cells possessed a metabolic and surface profile that was different from previously described SCVs or biofilm cells. The extracellular matrix was protein and extracellular DNA; but not polysaccharide. The SCV cells induced expression of certain surface proteins (such as Ebh) and lantibiotic synthesis while down-regulating factors that stimulates immune response (leucocidin, capsule, carotenoid). We also studied further their genetic characteristics. They possessed an increased viability in the presence of antibiotics compared to their non-SCV form. Their stability implied there had been genetic changes, we determined the whole genome sequence of WCH-SK2 and its stable SCV forms at a single base resolution, employing Single Molecular Real-Time (SMRT) sequencing that also enables the methylome to be determined. The genetic features of this isolate have been identified; the SCCmec type, the pathogenicity and genetic islands and virulence factors. The comparison has identified a set of genetic changes that occurred in the stable SCV form; most notably to the global regulator MgrA and the phosphoserine phosphatase RsbU (part of the regulatory pathway of the sigma factor SigB). There was a shift in the methylation across the genome. Conclusions: Our data reveal a cell heterogeneity within a S. aureus population and using conditions that resemble long-term survival in the host has identified a previously unnoticed S. aureus cell-type, with a distinctive metabolic and molecular profile. The results from this study represent a unique identification of a suite of epigenetic, genetic and transcriptional factors that are implicated in the switch in S. aureus to its persistent SCV form

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A new form of Staphylococcus aureus dormancy controlled by branched-chain amino acid availability in human macrophages

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