Repeated introduction of genetically modified Pseudomonas putida WCS358r without intensified effects on the indigenous microflora of field-grown wheat.

To investigate the impact of genetically modified, antibiotic-producing rhizobacteria on the indigenous microbial community, Pseudomonas putida WCS358r and two transgenic derivatives were introduced as a seed coating into the rhizosphere of wheat in two consecutive years (1999 and 2000) in the same field plots. The two genetically modified microorganisms (GMMs), WCS358r::phz and WCS358r::phl, constitutively produced phenazine-1-carboxylic acid (PCA) and 2,4-diacetylphloroglucinol (DAPG), respectively. The level of introduced bacteria in all treatments decreased from 10(7) CFU per g of roots soon after sowing to less than 10(2) CFU per g after harvest 132 days after sowing.

Effects of Pseudomonas putida modified to produce phenazine-1-carboxylic acid and 2,4-diacetylphloroglucinol on the microflora of field grown wheat.

Pseudomonas putida WCS358r, genetically modified to have improved activity against soil-borne pathogens, was released into the rhizosphere of wheat. Two genetically modified derivatives carried the phz or the phl biosynthetic gene loci and constitutively produced either the antifungal compound phenazine-1-carboxylic acid (PCA) or the antifungal and antibacterial compound 2,4-diacetylphloroglucinol (DAPG). In 1997 and 1998, effects of single introductions of PCA producing derivatives on the indigenous microflora were studied.