Bioproduction of low-pigment xanthan gum by a cell-wall deficient mutant of Xanthomonas campestris

This work aims to enhance the bioproduction of xanthan gum by screening a hyper-yield producer from the wild-type Xanthomonas campestris during a long-term continuous subculture. We reported a cell-wall deficient mutant, which performed a shift of cell morphology from rod-shaped to round-shaped. Both the yield of xanthan gum and the conversion rate of feedstock were assessed using sucrose as a carbon source with the supplement of yeast extract powder, l-glutamic acid, and other raw materials. After 96 h aerobic fermentation, the yield of xanthan gum of the mutant reached up to 32 g/L, which was 3.4 times of that of the wild-type strain. The conversion rate of feedstock in the mutant was up to 92.1%, which was 3 times of that of the wild-type (31.2%). Furthermore, pigments generated were determined and compared. As a result, the fermentation broth of the wild-type performed an OD_560nm of 0.296, which was 5.8 times of that (OD_560nm = 0.051) of the mutant. Microscopy analysis showed that the percentage of free-living cells in broth affected the color of the final product. Moreover, the robustness of the fermentation performance of the cell-wall deficient mutant at a pilot scale showed potential for industrial application.