Effect of genetically modified Pseudomonas fluorescens strains on the uptake of nitrogen by pea from 15N enriched organic residues

Abstract

The effects of an antibiotic-producing Pseudomonas flourescens strain (F113) carrying the marker gene cassette lacZY and a marked, non-producing strain (F113G22) on the uptake of nitrogen from 15N enriched organic residues incorporated into a sandy soil were investigated in microcosm studies. Strain F113 produces the antibiotic 2,4-diacetylphloroglucinol (DAPG), while its modified derivative strain F113G22 has DAPG production deleted by Tn5 mutagenesis. Uptake of nitrogen by pea (Pisum salivum) was estimated using isotope-ratio mass spectrometry. In addition, plant growth and microbial activity in soil were monitored. Both strains F113 and F113G22 enhanced the uptake of nitrogen from mineralized organic residues, even though the antibiotic producing strain F113 significantly reduced microbial activity in soil. It is suggested that the effect on nitrogen uptake was due to increased mineralization of organic residues by the introduced organisms, making greater quantities of inorganic nitrogen available for plant uptake. Unlike studies assessing impact in terms of perturbation to indigenous microbial communities, this study provides direct evidence of a change in ecosystem function as a results of the introduction of strains of a genetically marked bacterium, irrespective of whether its natural antibiotic- producing capacity has been genetically deleted.