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Abstract:
A gene cluster for exopolysaccharide (EPS) synthesis of Erwinia amylovora was cloned in cosmid pEA109 and identified by complementation of Erwinia stewartii mutants deficient in EPS−production (cps). A corresponding cluster from E. stewartii (pES2144) complemented EPS−mutants of E. amylovora (ams). Two EPS−dependent phages were used to characterize EPS synthesized in heterologously complemented mutants. An E. stewartii cpsC mutant carrying pEA109 produced mainly amylovoran in contrast to a cpsE−mutant complemented with pEA109 or to E. amylovora mutant D4 carrying pES2144, which produced predominantly stewartan, the EPS of E. stewartii. Lectin binding could also be used to detect amylovoran synthesis by heterologously complemented Erwinia mutants. Heterologous complementation of EPS−synthesis restored virulence to E. stewartii mutants but not to E. amylovora mutants. In addition to functional complementation, comparison of parts of nucleotide sequences from the ams and cps regions confirmed homologies between ams and cps genes
