Analysis of the prrAB two-component system regulatory effects on the lipid profile of Mycobacterium smegmatis

The prrAB two-component system has been shown to be essential for viability in Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis. To study this system, several prrAB mutants of Mycobacterium smegmatis, a close relative of Mtb, were created for study. These mutants included a deletion mutant complemented with prrA from Mtb controlled by Pmyc1_tetO, a deletion mutant, and a deletion mutant complemented with prrAB from M. smegmatis controlled by the native prrAB promoter sequence (~167 bp upstream sequence of prrAB). In a previous study, the prrAB deletion mutant clumped excessively relative to the wild-type strain when cultured in a nitrogen-limited medium. To address this irregularity, the lipid profiles of these mutants were analyzed through several experimental methods. Untargeted lipidomic profiles were analyzed by Electrospray Ionization Mass Spectrometry (ESI-MS). The ESI-MS data suggested the deletion mutant accumulates triacylglycerol species relative to the wild-type strain. This data was verified by thin-layer chromatography (TLC) and densitometry of the TLC images. The mycolic acid profile of each mutant was also analyzed by TLC but no noteworthy differences were found. High-throughput RNA-Seq analysis revealed several genes involved in lipid biosynthetic pathways upregulated in the prrAB deletion mutant, thus corroborating the ESI-MS and TLC data.