Abstract: DNA and protein sequences from Xanthomonas campestris pv. campestris, which may be targeted for activity reduction or enhancement using directed genetic engineering. Transformed microorganisms having reduced activity of at least one protein, e.g. galactomannanase, can be provided by disrupting a gene encoding the protein or introducing antisense nucleic acid sequence, providing xanthan gum essentially free of galactomannanase, amylase, cellulase or protease activity.