The genus Xanthomonas consists of 20 plant-associated species, many of which cause important diseases of crops and ornamental plants. Individual species comprise multiple pathovars, characterized by distinctive host specificity or mode of infection. Genomics is at the center of a revolution in Xanthomonas biology. Complete genome sequences are available for nine Xanthomonas strains, representing three species and five pathovars, including vascular and non-vascular pathogens of the important models for plant biology, Arabidopsis thaliana and rice. With the diversity of complete and pending Xanthomonas genome sequences, the genus has become a superb model for understanding functional, regulatory, epidemiological, and evolutionary aspects of host- and tissue-specific plant pathogenesis.
Further reading: Damien F. Meyer and Adam J. Bogdanove Chapter 7 in Plant Pathogenic Bacteria

Furthermore, Xanthomonas strains produce the acidic exopolysaccharide xanthan gum. Because of its physical properties, xanthan gum is widely used as a viscosifer, thickener, emulsifier or stabilizer in both food and non-food industries.
Further reading: Anke Becker and Frank-Jörg Vorhölter Chapter 1 in Microbial Production of Biopolymers and Polymer Precursors

Labels: bacteriology, bacterium, biopolymers, biotechnology, xanthan, xanthomonas

from Anke Becker and Frank-Jörg Vorhölter in Microbial Production of Biopolymers

Plant-pathogenic bacteria of the genus Xanthomonas are able to produce the acidic exopolysaccharide xanthan gum. Because of its physical properties, it is widely used as a viscosifer, thickener, emulsifier or stabilizer in both food and non-food industries. Xanthan consists of pentasaccharide repeat units composed of D-glucosyl, D-mannosyl, and D-glucuronyl acid residues in a molar ratio of 2:2:1 and variable proportions of O-acetyl and pyruvyl residues. The xanthan polymer has a branched structure with a cellulose-like backbone. Synthesis originates from glucose as substrate for synthesis of the sugar nucleotides precursors UDP-glucose, UDP-glucuronate, and GDP-mannose that are required for building the pentasaccharide repeat unit. This links the synthesis of xanthan to the central carbohydrate metabolism. The repeat units are built up at undecaprenylphosphate lipid carriers that are anchored in the cytoplasmic membrane. Specific glycosyltransferases sequentially transfer the sugar moieties of the nucleotide sugar xanthan precursors to the lipid carriers. Acetyl and pyruvyl residues are added as non-carbohydrate decorations. Mature repeat units are polymerized and exported in a way resembling the Wzy-dependent polysaccharide synthesis mechanism of Enterobacteriaceae. Products of the gum gene cluster drive synthesis, polymerization, and export of the repeat unit.

Further reading:
1. Microbial Production of Biopolymers
2. Plant Pathogenic Bacteria

Labels: bacterium, biopolymers, biotechnology, genetic engineering, xanthan, xanthomonas