AUTECOLOGY OF A GENETICALLY-MODIFIED FLUORESCENT PSEUDOMONAD ON SUGAR-BEET

The survival, dispersal and impact of a genetically modified microorga nism (GMM) in the phyllosphere of glasshouse grown sugar beet was inve stigated. The GMM, Pseudomonas fluorescens SBW25EeZY6KX (lacZY and kan '-xylE) derived from a bacterium originally isolated from field grown sugar beet, was introduced as a seed inoculum. It survived in the phyl losphere throughout the 531-day study on plants growing in field soil. The bacterium was highly competitive, in some samples representing th e largest bacterial population isolated. The GMM also established on a broad range of other plant species when introduced on the seed. Fluct uations 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 sign ificant effect on the number of GMMs detected in the phyllosphere, alt hough it affected the population size in the rhizosphere. The GMM pers isted in fallow soil for at least 10 days and subsequently colonised g erminating untreated plants. Limited potential for GMM dispersal from the phyllosphere was detected using physical means of transfer, althou gh moisture assisted dispersal from colonised plants. GMM transfer to other plant species growing between treated plants was detected. Insec ts 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 b acterial community colonising treated plants. Assessment of community diversity by fatty acid methyl ester (FAME) content of bacterial isola tes revealed that the GMM had less impact on the bacterial community t han the wild-type. Both organisms competitively excluded Enterobacteri aceae taxa, although this impact was attributed in part to the low tax a diversity that developed in the artificial conditions of the glassho use. Instances of the GMM undergoing phenotypic change after introduct ion on the seed were detected by FAME analysis.