CONICET | Buscador de Institutos y Recursos Humanos

In nature, the plant biomass is degraded by a processthat requires the cooperative action of multiple microorganisms capable ofproducing a variety of enzymes to attack the complex structure of lignocelluloses.This work assessed the production and the enzymatic activity over the main hemicellulolyticfraction of plant biomass, xylan, in monoculture and co-culture systems ofbacteria isolated from regional niches associated with sugar cane bagasse. Theenzyme activity was estimated by measuring reducing sugars released using thedinitrosalicylic acid method. All cultivation assays were performed at 200 rpmand 30 °C in a diluted peptone broth supplemented with 1% CMC (w/v). Theviability and the growth of both isolates were estimated by the number ofcolony forming units, fact that was possible since both isolates exhibiteddifferent colony morphology. The specific xylanolytic activity of theco-culture of Bacillus sp. AR03 and Paenibacillus sp. AR247 wasof 7.03 ± 0.46 IU/mg and 8.36 ± 0.49 IU/mg at 48 h and 96 h of cultivation,respectively. In contrast, each isolate assayed simultaneously under identicalconditions, produced significantly lower xylanase activities, even when bothisolates grew similarly in both, individual and co-cultures, reachingapproximately 1011 CFU/ml in all cases. These values were of 4.18 ± 0.24IU/mg and 4.55 ± 0.29 IU/mg of xylanolytic activity at 48 h and 96 h,respectively, for Bacillus sp. AR03, while Paenibacillus sp.AR247 reached values of 0.59 ± 0.09 IU/mg and 0.40 ± 0.03 IU/mg at the sameperiods of cultivation. When mixtures (1:1) of the cell-free supernatant ofindividual cultures were assayed, it was observed that the enzymatic activity reacheda maximum of 4.16 ± 0.39 IU/mg after 48 h of cultivation. This value was closeto that obtained by the sum of the enzymatic activity of individual cultures,which was 4.77 IU/mg, for the same cultivation time. The obtained results wereconsistent with the observation of a synergistic effect on the degradation ofxylan in the co-culture evaluated, with an estimated degree of synergism of1.69 at 96 h. This synergy, which has been described for enzyme mixtures onindustrial substrates, was observed here during the co-cultivation of Bacillussp. AR03 and Paenibacillus sp. AR247. This system displayed a higherxylanolytic activity with respect to the individual cultivation of each isolateand a different zymographic pattern along the cultivation period. The obtainedresults of the xylanolytic activity for individual strains and the co-culturemight indicate that the observed effect could not depend on an only addition ofenzyme activities so that we may suggest the existence of a synergistic cooperationduring the growth in the co-cultivation of the microorganism evaluated.