Comparative analysis of different xanthan samples by atomic force microscopy.

The polysaccharide xanthan which is produced by the γ-proteobacterium Xanthomonas campestris is used as a food thickening agent and rheologic modifier in numerous food, cosmetics and technical applications. Its great commercial importance stimulated biotechnological approaches to optimize the xanthan production. By targeted genetic modification the metabolism of Xanthomonas can be modified in such a way that the xanthan production efficiency and/or the shear-thickening potency is optimized. Using atomic force microscopy (AFM) the secondary structure of single xanthan polymers produced by the wild type Xanthomonas campestris B100 and several genetically modified variations were analyzed. We found a wide variation of characteristic differences between xanthan molecules produced by different strains. The structures ranged from single-stranded coiled polymers to branched xanthan double-strands. These results can help to get a better understanding of the polymerization- and secretion-machinery that are relevant for xanthan synthesis. Furthermore, we demonstrate that the xanthan secondary structure strongly correlates with its viscosifying properties.