In vitro cellulolytic activity of the plant pathogen Clavibacter michiganensis subsp. sepedonicus

The activity of four Clavibacter michiganensis subsp. sepedonicus strains against various cellulose substrates was investigated. Sixty-seven Clavibacter michiganensis subsp. sepedonicus strains grew well on media amended with carboxymethylcellulose, 64 strains produced zones of hydrolysis. Endoglucanase activity was optimal at 37 degrees C and pH 6.0 against carboxymethylcellulose incorporated in plate assays. Zymogram and sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed the presence of a protein band corresponding to the cellulolytic activity in the molecular weight (MW) range of approximately 28,000. Protein bands in the same range were detected in five Clavibacter michiganensis subsp. sepedonicus strains. Studies on crude enzyme extracts of Clavibacter michiganensis subsp. sepedonicus strain N-1-1 revealed that p-nitrophenyl beta-D-cellobioside (pNPC) was hydrolyzed, with optimal activity at 37 degrees C and pH 7.0.