A GENE-CLUSTER FOR AMYLOVORAN SYNTHESIS IN ERWINIA-AMYLOVORA - CHARACTERIZATION AND RELATIONSHIP TO CPS GENES IN ERWINIA-STEWARTII

A large ams gene cluster required for production of the acidic extrace llular polysaccharide (EPS) amylovoran by the fire blight pathogen Erw inia amylovora was cloned. Tn5 mutagenesis and gene replacement were u sed to construct chromosomal ams mutants. Five complementation groups, essential for amylovoran synthesis and virulence in E. amylovora, wer e identified and designated amsA-E. The ams gene cluster is about 7 kb in size and functionally equivalent to the cps gene cluster involved in EPS synthesis by the related pathogen Erwinia stewartii. Mucoidy an d virulence were restored to E. stewartii mutants in four cps compleme ntation groups by the cloned E. amylovora ams genes. Conversely, the E . stewartii cps gene cluster was able to complement mutations in E. am ylovora ams genes. Correspondence was found between the amsA-E complem entation groups and the cpsB-D region, but the arrangement of the gene s appears to be different. EPS production and virulence were also rest ored to E. amylovora amsE and E. stewartii cpsD mutants by clones cont aining the Rhizobium meliloti exoA gene.