Fate of the biological control agent Pseudomonas aureofaciens TX-1 after application to turfgrass

The fate and impact of Pseudomonas aureofaciens TX-1 following application as a biocontrol agent for fungi in turfgrass were studied. The organism was applied with a modified irrigation system by using a preparation containin g 1 X 10(6) P. aureofaciens TX-1 CFU ml(-1) about 100 times between May and August. We examined the impact of this repeated introduction of P. aureofa ciens TX-1 (which is known to produce the antimicrobial compound phenazine- 1-carboxylic acid) on the indigenous microbial community of the turfgrass s ystem and on establishment of introduced bacteria in the soil system. A PCR primer-DNA hybridization probe combination was developed to accurately mon itor the fate of P. aureofaciens TX-1 following application in irrigation w ater. To assess the impact of frequent P. aureofaciens TX-1 applications on the indigenous bacterial community, turfgrass canopy, thatch, and rhizosph ere samples were obtained during the growing season from control and treate d plots and subjected to DNA extraction procedures and denaturing gradient gel electrophoresis (DGGE). PCR amplification and hybridization of extracte d DNA with the P. aureofaciens TX-1-specific primerprobe combination reveal ed that P. aureofaciens TX-1 not only became established in the rhizosphere and thatch but also was capable of overwintering. Separation of PCR-amplif ied partial 16S rRNA genes by DGGE showed that the repeated application of P. aureofaciens TX-1 in irrigation water resulted in transient displacement of a leaf surface bacterial community member. There was no obvious alterat ion of any dominant members of the thatch and rhizosphere microbial communi ties.