THE XANTHOMONAS-CAMPESTRIS GUMD GENE REQUIRED FOR SYNTHESIS OF XANTHAN GUM IS INVOLVED IN NORMAL PIGMENTATION AND VIRULENCE IN CAUSING BLACK ROT

A cloned 4.1-kb EcoRI fragment from Xanthomonas campestris pv, campest ris was previously shown to complement the non-mucoid mutant P22 and i ncrease xanthan gum production after being transformed into the wild-t ype strain Xc17. The gene responsible for these effects was identified , sequenced, and shown to be the gumD gene which has previously been p roposed to encode glucose transferase activity, an enzyme required for adding the first glucose residue to the isoprenoid glycosyl carrier l ipid during xanthan synthesis, A gumD mutant, isolated from Xc17 by ge ne replacement, was shown to possess altered pigment xanthomonadin pro files and exhibit reduced virulence in causing black rot in broccoli. This study appears to be the first to demonstrate that interruption of a gene required for xanthan synthesis can lead to reduced virulence o f X. campestris. (C) 1997 Academic Press.