aurI/aurR system regulatory function in Pseudomonas chlororaphis GP72

Abstract:

[Background] Pseudomonas chlororaphis GP72 is a rhizobacteriaum that could produce phenazine antibiotics containing phenazine-1-carboxylic acid (PCA) and 2-hydroxyphenazine (2-OH-PHZ). Based on analyzing the whole-genome sequence, aurI/aurR regulatory system was found existed in GP72. [Objective] This article aims to study the regulation of aurI/aurR on phenazine production in GP72. [Methods] The aurI gene was heterologously expressed in Escherichia coli, then Chromobacterium violaceum CV026 and Agrobacterium tumefaciens NTL4 were used in plate assays. The knockout strains and complemental strains of aurI and aurR were constructed, and the growth curve and phenazine production of mutants were measured by fermentation. A transcriptional fusion plasmid was used to assess transcription level of promoter of phenazine synthesis gene cluster. [Results] The results of plate assays showed that aurI could produce a variety of signal molecules that could produce blue pigment in NTL4 and purple pigment in CV026. Fermentation results showed phenazine production of knock-out gene mutants were raised four times, and phenazine production of the complemental strains of aurI and aurR were reduced to the wild type level. It was found that the β-galactosidase activity fused with promoter of phenazine synthesis genes in the knock out strains were higher than that of the wild type. [Conclusion] aurI/aurR is a pair of negative regulation genes for phenazine in GP72. It could inhibit the transcription level of promoter of phenazine synthesis gene cluster, thereby affecting phenazine production.