INFLUENCE OF ENDOGENOUS PLASMIDS ON PHENOTYPES OF PANTOEA VAGANS STRAIN C91 ASSOCIATED WITH EPIPHYTIC FITNESS
J.M. Klein, J.E. Loper, V.O. Stockwell
Pantoea vagans strain C9-1 is an effective biological control agent for fire blight of pear and apple. C9-1 carries three circular plasmids: pPag1 (168 kb), pPag2 (166 kb), and pPag3 (530 kb). Of these, pPag3, a member of the large Pantoea plasmid family, was proposed to contribute to epiphytic fitness. We cured C9-1 of pPag2 and pPag3, individually and together, and compared phenotypes of the plasmid-cured derivatives to the wild-type C9-1 in laboratory assays. pPag3 carries genes for a yellow zeaxanthin pigment, and pigmentation is a known mechanism of UV protection in some bacteria. We found that UV-C tolerance did not differ between yellow-pigmented C9-1 and white derivatives lacking pPag3. Swarming motility, but not swimming, was influenced by both pPag2 and pPag3. C9-1 exhibited wide dendritic swarms that coalesced, whereas C9-1 lacking pPag3 formed thin dendritic swarms. Swarms of C9-1 lacking pPag2 exhibited less radial extension. In MBMA medium containing glucose, exopolysaccharide production and biofilm formation was greater by C9-1 lacking both pPag2 and pPag3 compared to the wild-type and C9-1 derivatives lacking only one plasmid. pPag2 and pPag3, both individually and together, influenced expression of phenotypes of C9-1 associated with epiphytic fitness and survival on plant surfaces.