Fastidian gum: the Xylella fastidiosa exopolysaccharide possibly involved in bacterial pathogenicity

The Gram-negative bacterium Xylella fastidiosa was the First plant pathogen to be completely sequenced. This species causes several economically impor tant plant diseases, including citrus variegated chlorosis (CVC). Analysis of the genomic sequence of X. fastidiosa revealed a 12 kb DNA fragment cont aining an operon closely related to the gum operon of Xanthomonas campestri s. The presence of all genes involved in the synthesis of sugar precursors, existence of exopolysaccharide (EPS) production regulators in the genome. and the absence of three of the X. campestris gum genes suggested that X. f astidiosa is able to synthesize an EPS different from that of xanthan gum. This novel EPS probably consists of polymerized tetrasaccharide repeating u nits assembled by the sequential addition of glucose-1-phosphate, glucose, mannose and glucuronic acid on a polyprenol phosphate carrier. (C) 2001 Fed eration of European Microbiological Societies. Published by Elsevier Scienc e B.V. All rights reserved.