Two Flagellar mutants of Xanthomonas campestris are characterized by enhanced xanthan production and higher xanthan viscosity

Xanthomonas campestris strains are used world-wide for the production of the industrially important exopolysaccharide xanthan. The high industrial relevance of xanthan can be explained by its extraordinary qualities as rheological control agent in aqueous systems and by its stabilizing properties in suspensions and emulsions. The phytopathogen Xanthomonas campestris is a motile bacterium with one polar flagellum. The flagellum is a cost intensive structure, in terms of energy and building block consumption. Based on the assumption that inhibition of the flagellar biosynthesis and related proton driven motility might be beneficial for the xanthan production in Xcc, two genes (fliC and fliM) were mutated to inhibit the motility. Both mutants Xcc JBL007 fliC- and Xcc JBL007 fliM- showed an increased xanthan production. Remarkably, the produced xanthan from both mutants showed enhanced rheological properties. While the chemical composition of the produced xanthan of the initial and both mutant strains did not change, notable differences in persistence length could be measured via atomic force microscopy. Results presented in this study demonstrate the possibility to further improve the xanthan production by Xcc through rational strain design.