Transcriptomic and Metabolomic Analysis of a Fusidic Acid-Selected fusA Mutant of Staphylococcus aureus

Abstract

Physiological experimentation, transcriptomics, and metabolomics were engaged to compare a fusidic acid-resistant Staphylococcus aureus mutant SH10001st-2 to its parent strain SH1000. SH10001st-2 harbored a mutation (H457Y) in the gene fusA which encodes the fusidic acid target, elongation factor G, as well as mutations in a putative phage gene of unknown function. SH10001st-2 grew slower than SH1000 at three temperatures and had reduced coagulase activity, two indicators of the fitness penalty reported for fusA-mediated fusidic acid- resistance in the absence of compensatory mutations. Despite the difference in growth rates, the levels of O2 consumption and CO2 production were comparable. Transcriptomic profiling revealed 326 genes were upregulated and 287 were downregulated in SH10001st-2 compared to SH1000. Cell envelope and transport and binding protein genes were the predominant functional categories of both upregulated and downregulated genes in SH10001st-2. Genes of virulence regulators, notably the agr and kdp systems, were highly upregulated as were genes encoding capsule production. Contrary to what is expected of mid-exponential phase cells, genes encoding secreted virulence factors were generally upregulated while those for adhesion-associated virulence factors were downregulated in SH10001st-2. Metabolomic analysis showed an overall increase in metabolite pools in SH10001st-2 compared to SH1000, mostly for amino acids and sugars. Slowed growth and metabolite accumulation may be byproducts of fusA mutation-mediated protein synthesis impairment, but the overall results indicate that SH10001st-2 is compensating for the H457Y fitness penalty by repurposing its virulence machinery, in conjunction with increasing metabolite uptake capacity, in order to increase nutrient acquisition.

Enterococcus faecalisOG1RF Evolution at Low pH Selects Fusidate-sensitive Mutants in Elongation Factor G and at High pH Selects Defects in Phosphate Transport

“…Acid-evolved fusA mutants are fusidate-sensitive at pH 7.0. In our acid-evolved clones, the gene that showed the most mutations encodes elongation factor G (fusA), an essential translation protein associated with virulence and biofilm formation (44)(45)(46). The ancestral strain OG1RF is resistant to fusidic acid, associated with the fusA mutation C316A (2).…”

“…We find that experimental evolution yields pH-adaptative mutations in a number of genes, notably those encoding elongation factor G ( fusA ) at low pH and the phosphate ABC transporter ( pstABC ) at high pH. Mutations in fusA may confer resistance to fusidic acid (35, 36); but our fusA mutants show a tradeoff of fusidate sensitivity. The pts loci are associated with virulence (37, 38).…”

Biochemical and Cellular Characterization of the Function of Fluorophosphonate-Binding Hydrolase H (FphH) in Staphylococcus aureus Support a Role in Bacterial Stress Response

“…Of note, a recent study reported the transcriptional response of an in vitro -evolved fusidic acid-resistant strain derived from S. aureus SH1000. 51 This strain carried mutations in the fus A gene, which encodes EF-G and a putative phage gene. The transcriptional analysis highlighted several significant findings.…”