Genes that influence fitness at high temperature. (A) Genes contributing to fitness at 43°C were classified by cellular function. Genes associated with the cell envelope constituted the largest fraction of the hits. (B) Six genes known to be associated with the heat-shock response were found to be temperature-sensitive. The number of reads in each gene normalized to 5 million sample reads is shown at the various temperatures tested. Loss of lyrA and mprF was found to have opposite phenotypes at 43°C, with an increase (C) and decrease (D) in fitness being observed, respectively. (E) To validate these phenotypes, null mutants in S. aureus HG003 were grown to mid-log phase, diluted, and grown at 43°C. While ΔmprF did not grow, confirming temperature sensitivity, the ΔlyrA strain grew at nearly twice the rate of WT.