[MvaT and MvaV transcriptionally regulate PcoI/PcoR quorum-sensing system in Pseudomonas fluorescens 2P24]

Pseudomonas fluorescens 2P24 is an effective biocontrol agent for soil-borne plant diseases caused by microbial pathogens. The PcoI/PcoR quorum-sensing system, which influences the colonization ability of 2P24 on wheat rhizosphere, is an important factor for disease suppression. In this study we performed random mutagenesis to screen novel regulators of the pcoI gene, a biosynthase gene responsible for N-acyl-homoserine lactone (AHL) production.

A gacA gene mutant carrying a pcoI-lacZ fusion was employed as the reporter strain and subjected to a random mini-Tn5 insertion mutagenesis. Expression of pcol kept at a low level under the gacA(-) negative background. The Tn5-mutants with increased pcoI transcription were selected.

Two mutants with significantly increased pcoI expression were identified from approximately 10000 Tn5-inserted colonies. The interrupted locus in the mutants was identified as the mvaT gene, a global regulator belonging to the H-NS family. A homolog of the mvaT gene, named mvaV, was also found in the genome draft sequence of 2P24. Genetic inactivation of mvaT or mvaV gene resulted in increased transcription of pcoI and the production of AHL molecules. Further qutitification by HPLC showed that the 2,4-diacetylphloroglucinol (2, 4-DAPG) levels in culture supernatant of the mvaT and mvaV mutants were significantly lower than that of the wild type strain. Furthermore, the mvaT or mvaV mutation drastically improved biofilm formation in 2P24.

MvaT and MvaV may function as an important regulatory complex controlling biocontrol capacity of P. fluorescens 2P24.