Autecology of a genetically modified fluorescent pseudomonad on sugar beet

Abstract

The survival, dispersal and impact of a genetically modified microorganism (GMM) in the phyllosphere of glasshouse grown sugar beet was investigated. The GMM, Pseudomonas fluorescens SBW25EeZY6KX (lacZY and kanr-xylE) derived from a bacterium originally isolated from field grown sugar beet, was introduced as a seed inoculum. It survived in the phyllosphere throughout the 531-day study on plants growing in field soil. The bacterium was highly competitive, in some samples representing the largest bacterial population isolated. The GMM also established on a broad range of other plant species when introduced on the seed. Fluctuations in the numbers of GMM correlated with those of the indigenous pseudomonad population, indicating the organism had not been adversely affected by the addition of novel genes. Inoculum density had no significant effect on the number of GMMs detected in the phyllosphere, although it affected the population size in the rhizosphere. The GMM persisted in fallow soil for at least 10 days and subsequently colonised germinating untreated plants. Limited potential for GMM dispersal from the phyllosphere was detected using physical means of transfer, although moisture assisted dispersal from colonised plants. GMM transfer to other plant species growing between treated plants was detected. Insects captured in the glasshouse carried the GMM, indicating a potential for long distance dispersal. Introduction of the wild-type and GMM on the seed had a transient impact on the number and composition of the bacterial community colonising treated plants. Assessment of community diversity by fatty acid methyl ester (FAME) content of bacterial isolates revealed that the GMM had less impact on the bacterial community than the wild-type. Both organisms competitively excluded Enterobacteriaceae taxa, although this impact was attributed in part to the low taxa diversity that developed in the artificial conditions of the glasshouse. Instances of the GMM undergoing phenotypic change after introduction on the seed were detected by FAME analysis.