Production and characterization of xanthan gum by Xanthomonas species isolated from plant leaves
This study screened Xanthomonas strains isolated from tomato, pepper, mango and banana with black rot spots for potential to produce xanthan gum. The leaves were washed in normal saline and tenfold dilution was prepared. Aliquots (1ml) were plated on Nutreint agar and incubated at 37˚C for 48h. Colonies with yellow pigmentation were gram stained. Gram negative rod bacteria were subjected to emulsification test. Isolates with yellow colonies, gram negative rods and which exhibited stable emulsion in carbon enriched medium were reagarded as potential xanthan gum producers. Eight (61.5%) of the isolates screened fulfil these conditions. Biochemical tests on the isolates revealed that the organism were Xanthomonas species and were coded accordingly (BX2, BX3, PX4, MX6, PX7, MX8, TM9, TX11). The best two strains (TM9 and BX3)were subjected to molecular analysis and were found to be Xanthomonas campestris CPBF 211 and Stenotrophomonas maltophilia IAE127. Xanthomonas campestris CPBF 211 and Stenotrophomonas maltophilia IAE127 were more efficient xanthan gum producers, yielding 21.01 g/l and 1.63 g/l of xanthan gum after 96 h. The xanthan gums produced were characterized by apparent viscosity, emulsification index, scanning electron microscopy (SEM), thermogravimetric analysis and differential scanning calorimetry and the results revealed little or no variations between the xanthan gum produced and the commercial xanthan gum. However, there was more apparent viscosity from xanthan gum by Stenotrophomonas maltophilia IAE127 (660.6 mPas) than those of Xanthomonas campestris CPBF 211 (526.1mPas) and commercial xanthan gum (411.3mPas) respectively. The results revealed that as the fermentation time increased the biomass also increased. The xanthan gum yield by the two organisms was found to increase from 0.92 to 7.6 g/l and 0.99 to 4.55 g/l under optimized conditions of pH: (9.0, 7.0), temperature (25̊C) carbon source (0.2% pineapple peels, 0.2% sugarcane bagasse) and nitrogen source (yeast extract) respectively. The gums exhibited good thermal stability and were structurally similar. The results suggest that Xathomonas species are good candidates for xanthan gum production.