Effects of insertional inactivation of gacS gene on two secondary metabolites in Psedomonas chlororaphis G-05

Abstract:

Phenazine-1-carboxylic acid biosynthesized and secreted by Pseudomonas chlororaphis G-05 isolated from the rhizosphere of pepper in greenhouse (Huaian, China), contributes to its biological suppression of R. solani growth. [Objective] Our aim is to elucidate its biocontrol function and regulation mechanism. [Methods] We first identified the strain with biochemical method and homology comparison of 16S rDNA. A conservative DNA fragment of gacS gene was then obtained from the genomic DNA of the wild type strain G-05 by polymerase chain reaction (PCR). According to homologous recombination technology, a mutant G-05S was then created with insertional inactivation of gentamycin resistance cassette (aacC1). [Results] In comparison with the wild type strain G-05, the gacS-deficient mutant G-05S produced trace amount of phenazine-1-carboxylic acid in King’ s B（KMB）or Pigment Production Medium( PPM) medium, respectively. However, it produced indole-3-acetic acid (IAA) in the same way as the wild type strain. When the gacS gene was introduced with the shuttle vector pME6032, the mutant G-05S produced the same phenazine-1-carboxylic acid as the wild type strain. [Conclusion] The regulation mediated by gacS gene on secondary metabolites is specific and differential in some biocontrol agents.