Construction of a recombinant strain of Pseudomonas fluorescens producing both phenazine-1-carboxylic acid and cyclic lipopeptide for the biocontrol of take-all disease of wheat

Abstract

The primary mechanism of biocontrol by Pseudomonas fluorescens strains HC1–07 and HC9–07 is production of a cyclic lipopeptide (CLP) and phenazine-1-carboxylic acid, respectively. We introduced the seven-gene operon for the synthesis of phenazine-1-carboxylic acid (PCA) from P. synxantha 2–79 into Pseudomonas fluorescens HC1–07rif to determine if the biocontrol activity of the recombinant strain HC1–07PHZ increased against Gaeumannomyces graminis var. tritici, causal agent of take-all disease of wheat. In vitro inhibition assays showed that strain HC1–07PHZ consistently inhibited the hyphal growth of three isolates of the take-all pathogen on plates of both PDA and KMB, and the recombinant consistently inhibited G. graminis. var. tritici to a greater extent than the wild type. Strain HC1–07PHZ applied at a dose of 102 CFU seed−1 suppressed take-all better than strains HC1–07rif and HC9–07rif applied either individually or in combination. When the dose of the bacteria was increased to 104 CFU seed−1, the strain combination HC1–07rif + HC9–07rif showed significantly better disease suppression than did HC1–07rif, HC9–07rif or HC1–07PHZ applied individually. However, when the bacterial dose was increased to 107 CFU seed−1, strains HC1–07rif and HC1–07PHZ showed significantly better disease suppression than HC9–07rif and the combination HC1–07rif + HC9–07rif.