Detection and characterisation of genetically modified Pseudomonas from the phylloplane of Beta vulgaris L.
Colonisation of the leaf surface of sugar beet by different pseudomonad strains has been examined using both bioluminescence (lux) and xylE marker systems. The use of bioluminescence as a method of detection allows the fate of an introduced microbial population to be monitored using both colony counts and metabolic activity. Colonisation of the sugar beet plant, using both seed and leaf inoculation, has been correlated with the stage of leaf development. Competition between introduced pseudomonads with different marker systems has also been studied. Having confirmed that there are significant differences in the pattern of colonisation between the different isolates, the factors thought to confer epiphytic fitness on bacteria from the leaf surface have been investigated. These include characteristics such as extracellular polysaccharide (EPS) production, motility, siderophore production and the ability to withstand osmotic stress. Differences between the pseudomonad strains were found for each of these features. Particular interest has developed in EPS production and this has been studied further using electron microscopy, chemical and molecular assays. Differences in alginate production between the pseudomonad species have been found using an algD promoter-xylE fusion vector. A link between increased levels of alginate production and desiccation stress has been determined and it is possible to correlate this feature with successful colonisation of the leaf surface.