The diseases caused by Xylella fastidiosa are associated with aggregation of the bacteria in xylem vessels, formation of a gummy matrix and subsequent blockage of water uptake. In the closely related pathogen, Xanthomonas campestris, xanthan gum is known to be an important virulence factor, probably contributing to bacterial adhesion, aggregation and plugging of xylem. Xanthan gum, produced by X. campestris, is an extracellular polysaccharide consisting of a cellulose backbone (β-1,4-linked D-glucose) with trisaccharide side chains composed of mannose, glucuronic acid and mannose attached to alternate glucose residues in the backbone. We had constructed a mutant of X. campestris lacking gumI gene that is responsible for adding the terminal mannose for producing modified xanthan gum which is similar to xanthan gum from X. fastidiosa. The modified xanthan gum degrading endophytic bacterium Acinetobacter johnsonii GX123 isolated from the oleander infected with leaf scorch disease.