Effects of Nonionic Surfactants on Xanthan Gum Production: a Survey on Cellular Interactions

BACKGROUND: Xanthomonas campestris is a biopolymer producing gram negative bacterium. Production of xanthan biopolymer can be affected by different extrinsic factors as well as surfactants. Hitherto, effects of nonionic surfactants on xanthan production have been studied in a limited number of articles. OBJECTIVE: In the present study, nonionic surfactants were used to pursue their effects on improvement of xanthan production. Moreover, a number of cellular consequences upon the treatment were investigated with impacts on gum production. MATERIALS AND METHODS: Effects of different nonionic surfactants (Tween 20, Tween 80 and Triton X100) on xanthan production and Xanthomonas campestris cells were assessed by ultramicroscopy (SEM), changes in culture turbidity, leakage of sugars and ATP, and quality of xanthan (i.e. pyruvate content and determination of polymer molecular weight). RESULTS: The nonionic surfactant Tween 20 increased ATP (3.2 folds) and sugar leakage (3.1 folds). Furthermore, they caused cell shape alteration. Tween 80 improved both xanthan production (11 g.L(-1)) and viscosity of the product (1368 cP), while the total biomass remained unchanged (2.2 g.L(-1)). Molecular weight of xanthan was enhanced (from 23 to 59 million Da). Toxic effect of 5% (v/v) Triton X 100 decreased the turbidity of culture to 120 NTU and total biomass was diminished to 1 g.L(-1). Tween 20 caused the loss of ATP and sugar leakage and led to lower xanthan production. It had no effect on biomass content. CONCLUSIONS: In general, amounts of surfactants that bacterial cells can tolerate seem to be helpful in substrate and metabolite transportation, and enzyme activities involved in xanthan biosynthesis and release. Surfactants induce harsh damages to cell barriers, preventing the growth and adversely affecting quantity and quality of xanthan gum.