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Characterization of the Extracellular Polysaccharide Produced by Clavibacter michiganensis subsp. michiganensis. R. W. van den Bulk, Centre for Plant Breeding Research, P.O. Box 16, 6700 AA Wageningen, The Netherlands; L. P. T. M. Zevenhuizen(2), J. H. G. Cordewener(3), and J. J. M. Dons(4). (2)Laboratory of Microbiology, Agricultural University, Wageningen, The Netherlands; (3)(4)Centre for Plant Breeding Research, P.O. Box 16, 6700 AA Wageningen, The Netherlands. Phytopathology 81:619-623. Accepted for publication 26 December 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-619.

An extracellular polysaccharide (EPS) produced by Clavibacter michiganensis subsp. michiganensis, the causal agent of bacterial canker in tomato, was isolated from culture filtrates by ultrafiltration. The components of EPS were shown to be l-fucose, d-galactose, d-glucose, pyruvate, succinate, and acetate in the approximate molar ratio of 2:1:1:1:0.5:1.5. Methylation analysis revealed that the tetrasaccharide-repeating unit consisted of one 1,3-linked glucosyl, one 1,4-linked fucosyl, one 1,3,4-linked fucosyl (branch unit) and one 1-linked galactosyl residue (terminal group). Pyruvate occupied the O-4 and O-6 position of the galactosyl residue, whereas the positions of the succinyl and O-acetyl substituents are, as yet, undetermined. These results indicate that the structure of the EPS, as far as the carbohydrate portion is concerned, is identical to that of the EPS of C. m. subsp. insidiosus, except for the presence of the succinyl and O-acetyl groups, which were not observed in the latter. Gel filtration chromatography demonstrated the molecular weight of the EPS to be variable, with sizes of about 106 and 107 Da. The high molecular weight of the EPS may be associated with the wilting symptoms shown by infected plants. Evidence is given that a high-molecular-weight EPS produced in planta is similar in composition to EPS produced in vitro.

Additional keywords: bacterial canker of tomato, Lycopersicon esculentum.