The opgGH genes regulate 2,4-diacetylphloroglucinol production in Pseudomonas fluorescens 2P24

Abstract:

[Objective] The polyketide antibiotic 2,4-diacetylphloroglucinol (2,4-DAPG) is essential for the biocontrol effect of Pseudomonas fluorescens 2P24. However, the genetic elements that modulates 2,4-DAPG production remains to be ascertained. [Methods] Previously, Tn5 transposon mutagenesis was employed to get P. fluorescens W3 with the complete loss of antagonism to Rhizoctonia solani, and the strain W3 was then used to screen out the novel gene that influencing the production of 2,4-DAPG. In this study, the effect of the mutated gene in W3 on the 2,4-DAPG production and biocontrol effect of 2P24 was explored. [Results] One of the insertion mutations, exhibiting no activity against R. solani, was mapped to opgG, which encodes the protein for the synthesis of osmoregulated periplasmic glucan (OPG). The deletion of opgGH impaired the production of 2,4-DAPG and bacterial swimming motility, while it did not affect the production of quorum sensing (QS) signals, the generation of hydrocyanic acid, or the biofilm formation. The transcriptional fusion assay indicated that the expression levels of rsmY, rsmX1, and gacA were not changed in the opgGH mutant compared with the wild type. The data suggested that opgGH regulated the production of 2,4-DAPG in a Gac/Rsm-independent manner. [Conclusion] The opgGH operon is essential for the regulation of 2,4-DAPG production, swimming mobility, and antifungal effect, serving as a key regulator for the biocontrol capacity of P. fluorescens 2P24.