Monitoring differences in gene expression levels and polyhydroxyalkanoate (PHA) production in Pseudomonas putida KT2440 grown on different carbon sources

Pseudomonas putida has a variety of potential uses in bioremediation and biosynthesis of biodegradable plastics. P. putida is able to utilize a wide range of carbon sources. In this study, P. putida KT2440 was grown on glucose, glycerol, citrate, or fatty acid (lauric acid) as the sole carbon source. Differences in expression levels of genes involved in the Entner-Doudoroff pathway, glycerol metabolism, TCA cycle and β-oxidation were detected using quantitative real-time PCR. When glycerol was the sole carbon source, expression of genes related to glycerol metabolism was enhanced with the exception of the negative regulon gene glpR. There were no significant differences in expression levels of genes that putatively encode enzymes involved in the Entner-Doudoroff pathway for cells grown on glucose as compared to cells grown on other carbon sources. Exceptions to this trend were the ABC transporter genes. Genes encoding enzymes selected from the TCA cycle all showed higher expression levels in cells grown on citrate. Two genes for β-oxidation enzymes, fadB and the long-chain fatty acid transporter gene, showed higher expression level when cells were grown on lauric acid. Genes encoding enzymes involved in PHA synthesis, phaC1, phaC2, phaZ, and phaJ4, all showed higher expression levels when cells were grown on lauric acid. This study has identified genes involved in the metabolism of different carbon sources and PHA synthesis. This information will be invaluable to understand how genes are regulated and construct transgenic strains to utilize carbon sources more efficiently and better produce PHAs.