Monitoring gfp-tagged bacterial antagonists in the rhizosphere of tomato plants

Gfp tagging of four bacterial antagonists of Ralstonia solanacearum (biovar 2, race 3) was achieved with the IncQ plasmid pSM1890 (Gm, Sm, gfp) wich was acquired in triparential matings. The green fluorescent protein was formed in all antagonists (Pseudomonas putida, Enterobacter sp.) although the colonies showed different brightness of green fluorescence. The presence of the IncQ plasmid was confirmed by PCR with IncQ specific primers. The survival and colonisation patterns of plating and confocal laser scanning microscopy. Selective plating indicated that all strains had a good rhizosphere competence and were still detectable 29 days after inoculation at levels between 10⁶ and 10⁷ cells per gram of root fresh weight. In contrast, confocal laser scanning microscopy (CLSM) analysis revealed that only rather few green fluorescent cells were detectable at this time poimt wich might indicate a low metabolic activity of the inoculant strains. Five days after inoculation the roots showed large numbers of green cells and similar colonisation patterns were observed for all antagonists.