Seleção de linhagens selvagens de Xanthomonas sp. para produção de goma xantana em manipueira

Abstract

The commercial importance of the xanthan gum biopolymer has stimulated studies based on its production from alternative carbon sources, selection of new strains and adaptation of the optimal conditions of growth and production. In this context, the present study aimed to select strains of Xanthomonas spp. isolated from mango leaf tissues (Mangifera indica), for the production of xanthan gum. In addition, to assessing the feasibility of using the manipueira agroindustrial residue as a partial or total substitute for sucrose in the xanthan gum production process. The bacterial isolates were reactivated in a semi-selective SMR medium, and subsequently subjected to morphological characterization, Gram differential staining test, and biochemical tests. It was observed that 4 isolates presented characteristics consistent with those described in the literature for the genus Xanthomonas, such as: small size, circular shape, convex elevation, smooth edges, smooth structure, translucent shine, yellow color, and viscous aspect, rod-shaped and were negative oxidase, positive motility, positive catalase, positive hydrogen sulfide production, indole production and starch hydrolysis, positive, being: MN18, MN23.1, MN24 and MN37.2. Growth curves were constructed for the control strain Xanthomonas campestris XC4.1 and for the 4 selected isolates, determining the inoculum volume of subsequent fermentation processes, as well as the optimum growth period of the strains, which occurred between 4 and 72 hours. The selection of the gum producing lines was carried out in fermentations, using sucrose as a carbon source, and the experiments were conducted under agitation of 120 rpm / 28 ° C for the production of the inoculum and 180 rpm for the production of the gum. The four strains produced the gum, with yields of 4.60 g/L, 18.49 g/L, 47.22 g/L and 50.69 g/L for MN24, MN18, MN23.1, MN37.2, respectively. The control strain provided a yield of 44.98 g/L. MN37.2 was selected based on the production of xanthan gum using manipueira in substitution to sucrose in a two-factor mixing experiment through Simplex Lattice mixture analysis. The experimental runs took place at 180 rpm / 28 ° C / 96 hours. The manipueira was characterized physically-chemically, presenting 93.42% of moisture content. The contents of carbohydrates, ashes, protein and lipids were 2.54%, 1.61%, 1.07%, 0.36%, respectively. For the optimization experiment, the linear model proved to be the most suitable for the production of xanthan gum. According to the desirability, the best formulation observed presented a ratio of 100: 0 of manipueira: sucrose, thus demonstrating that this residue has viability to be used as a substitute for sucrose in processes for obtaining xanthan gum.