ALTERED EPIPHYTIC COLONIZATION OF MANNITYL OPINE-PRODUCING TRANSGENICTOBACCO PLANTS BY A MANNITYL OPINE-CATABOLIZING STRAIN OF PSEUDOMONAS-SYRINGAE

The plasmid pYDH208, which confers the ability to catalbolize the mann ityl opines mannopine and agropine, was mobilized into the nonpathogen ic Pseudomonas syringae strain Gin. The growth of the mannityl opine-c atabolizing strain Cit7(pYDH208) was compared with that of the near-is ogenic non-opine-catabolizing strain Cit7xylE on leaves of wild-type t obacco (Nicotiana tabacum cv. Xanthi) and transgenic mannityl opine-pr oducing tobacco plants (N. tabacum cv. Xanthi, line 2-26). The populat ion size of Cit7(pYDH208) was significantly greater on the lower leave s of transgenic plants than on middle or upper leaves of those plants. The population size of Cit7(pYDH208) on lower leaves of transgenic pl ants was also significantly greater than the population size of Cit7xy lE on similar leaves of wild-type plants. High-voltage paper electroph oresis demonstrated higher levels of mannityl opines in washings from lower- and mid-level leaves than in washings from upper-level leaves. The ability of Cit7(pYDH208) to catabolize mannityl opines in the carb on-limited phyllosphere increased the carrying capacity of the lower l eaves of transgenic plants for Cit7(pYDH208). In coinoculations, the i ncrease in the ratio of population sizes of Cit7(pYDH208) to Cit7xylE on transgenic plants was apparently due to a subtle difference in the growth rates of the two strains and to the difference in final populat ion sizes. An ability to utilize additional cai bon sources on the tra nsgenic plants also enabled Cit7(pYDH208) to achieve a higher degree o f coexistence with Cit7xylE on transgenic plants than on wild-type pla nts. This supports the hypothesis that the level of coexistence betwee n epiphytic bacterial populations can be altered through nutritional r esource partitioning.