Description:
<jats:title>Summary</jats:title><jats:p><jats:styled-content style="fixed-case">PlsX</jats:styled-content> is an acyl‐acyl carrier protein (<jats:styled-content style="fixed-case">ACP</jats:styled-content>):phosphate transacylase that interconverts the two acyl donors in Gram‐positive bacterial phospholipid synthesis. The deletion of <jats:styled-content style="fixed-case"><jats:italic>plsX</jats:italic></jats:styled-content> in <jats:styled-content style="fixed-case"><jats:italic>S</jats:italic></jats:styled-content><jats:italic>taphylococcus aureus</jats:italic> results in a requirement for both exogenous fatty acids and <jats:italic>de novo</jats:italic> type <jats:styled-content style="fixed-case">II</jats:styled-content> fatty acid biosynthesis. Deletion of <jats:styled-content style="fixed-case"><jats:italic>plsX</jats:italic></jats:styled-content> (<jats:styled-content style="fixed-case">SP</jats:styled-content>0037) in <jats:styled-content style="fixed-case"><jats:italic>S</jats:italic></jats:styled-content><jats:italic>treptococcus pneumoniae</jats:italic> did not result in an auxotrophic phenotype. The Δ<jats:styled-content style="fixed-case"><jats:italic>plsX</jats:italic> <jats:italic>S</jats:italic></jats:styled-content><jats:italic>. pneumoniae</jats:italic> strain was refractory to myristic acid‐dependent growth arrest, and unlike the wild‐type strain, was susceptible to fatty acid synthesis inhibitors in the presence of exogenous oleate. The Δ<jats:styled-content style="fixed-case"><jats:italic>plsX</jats:italic></jats:styled-content> strain contained longer chain saturated fatty acids imparting a distinctly altered phospholipid molecular species profile. An elevated pool of 18‐ and 20‐carbon saturated fatty acids was detected in the Δ<jats:styled-content style="fixed-case"><jats:italic>plsX</jats:italic></jats:styled-content> strain. A <jats:styled-content style="fixed-case"><jats:italic>S</jats:italic></jats:styled-content><jats:italic>. pneumoniae</jats:italic> thioesterase (<jats:styled-content style="fixed-case">TesS</jats:styled-content>, <jats:styled-content style="fixed-case">SP</jats:styled-content>1408) hydrolyzed acyl‐<jats:styled-content style="fixed-case">ACP</jats:styled-content> <jats:italic>in vitro</jats:italic>, and the Δ<jats:italic>tesS</jats:italic> Δ<jats:styled-content style="fixed-case"><jats:italic>plsX</jats:italic></jats:styled-content> double knockout strain was a fatty acid auxotroph. Thus, the <jats:styled-content style="fixed-case">TesS</jats:styled-content> thioesterase hydrolyzed the accumulating acyl‐<jats:styled-content style="fixed-case">ACP</jats:styled-content> in the Δ<jats:styled-content style="fixed-case"><jats:italic>plsX</jats:italic></jats:styled-content> strain to liberate fatty acids that were activated by fatty acid kinase to bypass a requirement for extracellular fatty acid. This work identifies <jats:italic>tesS</jats:italic> as the gene responsible for the difference in exogenous fatty acid growth requirement of the Δ<jats:styled-content style="fixed-case"><jats:italic>plsX</jats:italic></jats:styled-content> strains of <jats:styled-content style="fixed-case"><jats:italic>S. aureus</jats:italic></jats:styled-content> and <jats:styled-content style="fixed-case"><jats:italic>S</jats:italic></jats:styled-content><jats:italic>. pneumoniae</jats:italic>.</jats:p>