Transformation of Pseudomonas fluorescens with genes for biosynthesis of phenazine-1-carboxylic acid improves biocontrol of rhizoctonia root rot and in situ antibiotic production.

A seven-gene operon for the synthesis of phenazine-1-carboxylic acid was introduced into Pseudomonas fluorescens Q8r1-96, an aggressive root colonizer that produces 2,4-diacetylphloroglucinol and consistently suppresses take-all of wheat. The recombinant strains produced both antifungal metabolites and maintained population sizes comparable to those of Q8r1-96 over a seven-week period in the rhizosphere of wheat. The strains were no more suppressive of take-all or Pythium root rot than was Q8r1-96, but suppressed Rhizoctonia root rot at a dose of only 10(2) CFU per seed, one to two orders of magnitude lower than the dose of Q8r1-96 required for comparable disease control.