SCREENING OF XANTHOMONAS SPECIES FOR XANTHAN GUM PRODUCTION

Abstract

Xanthomonas campestris are plant pathogens causing various disease such citrus canker, black rot disease and bacterial leave blight, xanthan gum is an extracellular heteropolysaccharides produced by Xanthomonas species through the fermentation of carbohydrates. This study aimed at screening Xanthomonas strains isolated from diseased plant leaves (tomato, pepper, mango rice and banana leaves) for potential to produce xanthan gum. Leaves with black rot spots were collected from the plants in selected farms within Niger state (Nanni village in Kaffi LGA, Badeggi in Bida LGA and Chanchaga in Bosso LGA) and transported to the research laboratory. The leaves were washed in normal saline and tenfold dilution was prepared. Aliquots (1mL) were plated on nutrient agar and incubated at 37˚C for 48h. Yellow pigmented bacteria colonies that appeared Gram negative rod after Gram staining were subjected to emulsification test. Isolates with yellow pigmentation, Gram negative rods and which exhibited stable emulsion in carbon enriched medium were regarded as potential xanthan gum producers. Eight (61.5%) of the isolates screened fulfiled these conditions. Biochemical tests on the isolates revealed that the organisms were Xanthomonas species. The best two xanthan gum producing isolates were further identified by molecular techniques as Xanthomonas campestris CPBF 211 and Stenotrophomonas maltophilia IAE127. Xanthomonas campestris CPBF 211 and Stenotrophomonas maltophilia IAE127 yielded 2.10 g/L and 1.63 g/L respectively of xanthan gum after 96 h. The xanthan gum as well as the biomass yield by the two organisms were found to increase (4.51-7.26 g/L and 6.50-6.80 g/L respectively) 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 xanthan gums produced were characterized and the results showed not much variation between the xanthan gum produced and the commercial xanthan gum. However, the apparent viscosity of xanthan gum produced by Stenotrophomonas maltophilia IAE127 (660.6 mPas) was higher than those of Xanthomonas campestris CPBF 211 (526.1mPas) and commercial xanthan gum (411.3mPas). Besides, the ability of xanthan gum from Stenotrophomonas maltophilia IAE127 and Xanthomonas campestris CPBF 211 to emulsify hydrocarbon, vegetable oils, crude oil and diesel was similar to commercial xanthan gum. All the gums exhibited good thermal stability. Xanthan gum produced by the two organisms were found to recover less crude oil from the soil.