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

A huge variety of biopolymers, such as polysaccharides, polyesters, and polyamides, are naturally produced by microorganisms. These range from viscous solutions to plastics and their physical properties are dependent on the composition and molecular weight of the polymer. The genetic manipulation of microorganisms opens up an enormous potential for the biotechnological production of biopolymers with tailored properties suitable for high-value medical application such as tissue engineering and drug delivery.

Microorganisms naturally produce a wide variety of carbohydrate molecules, yet large-scale manufacturing requires production levels much higher than the natural capacities of these organisms. Metabolic engineering efforts generate microbial strains capable of meeting the industrial demand for high synthesis levels. As both oligosaccharide and polysaccharide synthesis are carbon and energy-intensive processes, improved production of these products require similar metabolic engineering strategies. Metabolically engineered strains have successfully produced many carbohydrate products and many unexplored strategies made available from recent progress in systems biology can be used to engineer better microbial catalysts.

Further reading: Microbial Production of Biopolymers and Polymer Precursors

Labels: biopolymers, biotechnology, genetic engineering