Avaliação do potencial celulolítico de fungos filamentosos do bioma cerrado visando à produção de bioetanol

Abstract

Currently, there is a growing interest in cellulosic ethanol production, and is a promising alternative to fossil fuels. New cellulase-producing sources such as fungi have been investigated, however, those associated with decomposing foliar debris are little studied in this sense. In this context, the objective was to evaluate the production of the cellulolytic complex by filamentous fungi associated with decomposing foliar debris in the stream and to select an isolate in order to optimize the cellulase production for later application in the hydrolysis of lignocellulosic materials. A total of 27 isolates were submitted to submerged fermentation in the presence of carboxymethylcellulose for seven days at 35 ° C and constant agitation at 150 rpm and the highest total cellulase activity were identified by sequencing of the rDNA ITS region. The selected isolate to optimize the production cellulases was initially performed a Placket-Burman planning for the screening of significant variables, then these were optimized applying a rotational central compound design. The best cellulase production condition was defined this was used in the culture of the isolate and the crude enzyme extract thus obtained, used for partial biochemical characterization. From the knowledge of the conditions of the best activity of the total cellulase, the crude enzymatic extract as well as a commercial enzymatic preparation were applied in the hydrolysis of sugarcane bagasse and rice husk, both pretreated with hydrogen peroxide in medium the production of reducing sugars. The 27 isolates studied produced cellulases; however, eight presented the best activity, ranging from 0.272 to 0.343 U / mL, 0.355 to 0.485 U / mL, and 0.250 to 0.335 U / mL, respectively, for total cellulase, endoglicanase and exoglycanase. From the sequencing of the ITS region of the rDNA, these isolates were identified, namely, Aspergillus sydowii, Cladosporium sp., Paraphaeosphaeria arecacearum, Penicillium simplicissimum and Penicillium citrinum. The production of cellulases by Paraphaeosphaeria arecacearum, the new source of cellulases identified in the present study, was optimized obtaining maximum yield in the presence of 4 gL-1 peptone, pH 4.0 and 11 days of cultivation, being 6, 32 U.g-1 ss for total cellulase, 7.58 U.g-1 ss for endoglycanase and 5.08 U.g-1 ss for exoglycanase. The partial biochemical characterization of the crude enzyme extract indicated an optimal activity for total cellulase and endoglycanase at pH 5.5 and temperature 50 ° C and for exoglicanase at pH 5.0 and temperature of 45 ° C. The crude enzymatic extract was used in the hydrolysis of sugarcane bagasse and rice hulls, and after 72 hours of hydrolysis, the production of total reducing sugars was 60.7 mg.g-1 in the presence of sugarcane bagasse and 37.2 mg.g-1 when the rice husk was used, which corresponds to efficiency respectively, 51% and 61.7% lower than the crude extract when compared to commercial preparation. Paraphaeosphaeria arecacearum shows promise in the hydrolysis of lignocellulosic materials with the objective of producing biofuels. It is important to note the importance of the results obtained in this work as a basic research, since there are no reports in the literature about the production of cellulases by Paraphaeosphaeria arecacearum.