Characterization of Molecular Mechanisms Controlling <em>fabAB</em> Transcription in <em>Pseudomonas aeruginosa</em>

<div><h3>Background</h3><p>The FabAB pathway is one of the unsaturated fatty acid (UFA) synthesis pathways for <em>Pseudomonas aeruginosa</em>. It was previously noted that this operon was upregulated in biofilms and repressed by exogenous UFAs. Deletion of a 30 nt <em>fabA</em> upstream sequence, which is conserved in <em>P. aeruginosa</em>, <em>P. putida</em>, and <em>P. syringae</em>, led to a significant decrease in <em>fabA</em> transcription, suggesting positive regulation by an unknown positive regulatory mechanism.</p> <h3>Methods/Principal Findings</h3><p>Here, genetic and biochemical approaches were employed to identify a potential <em>fabAB</em> activator. Deletion of candidate genes such as <em>PA1611</em> or <em>PA1627</em> was performed to determine if any of these gene products act as a <em>fabAB</em> activator. However, none of these genes were involved in the regulation of <em>fabAB</em> transcription. Use of <em>mariner</em>-based random mutagenesis to screen for <em>fabA</em> activator(s) showed that several genes encoding unknown functions, <em>rpoN</em> and DesA may be involved in <em>fabA</em> regulation, but probably via indirect mechanisms. Biochemical attempts performed did fail to isolate an activator of <em>fabAB</em> operon.</p> <h3>Conclusion/Significance</h3><p>The data suggest that <em>fabA</em> expression might not be regulated by protein-binding, but by a distinct mechanism such as a regulatory RNA-based mechanism.</p>