The Influence Of The Global Regulatory Genes QscR And GacA On The Secondary Metabolism In Pseudomonas Sp.M18

The Pseudomonas sp. M18, isolated from the watermelon rhizosphere, is antagonistic against a number of soil-borne pathogens. This capability is primarily due to its ability to produce several antibiotics such as pyoluteorin (Plt), phenazine-1-carboxylic acid (PCA) and so on. This research project focused on the regulatory mechanism of the global regulatory genes qscR and gacA on the secondary metabolites including PCA and Plt, and then constructed engineering strains with improved PCA production and bio-control capability. In this study, we constructed the qscR mutant strain, examined its impact on the PCA and Plt biosynthetic expression. The results showed that qscR gene could differentially regulate PCA and Plt biosynthetic expression and had intensely negative regulation on PCA production. Thus, we constructed the engineering strain M18Q with improved PCA production. Meanwhile, we also further explored the function of the gacA gene considering both width and depth. On one hand, I further developed the work on the regulatory mechanisms of the gacA gene on the expression of two phenazine biosynthetic clusters, by constructing reporter fusions and RT- PCR methods. The results indicated that gacA could negative regulate the mRNA synthesis of phenazine biosynthetic gene clusters in total while gacA showed differentially influence on two phenazine clusters On the other hand, I identified some new targets for gacA gene's regulation including the Plt production, quorum-sensing systems activities, cell motility abilities, pigment production, and siderphores secretion. Finally, through constructing transcriptional fusions, I also examined the relationship between qscR and gacA genes, whose mutants all showed high PCA production. The results indicated that qscR gene functioned as an intermediate in gacA-dependent PCA expression regulation.