Evaluation of the influence of carbon sources on cellulases and xylanases production by microbacterium sp.

Abstract

The lignocellulose is one of the main constituents of vegetable biomass. Besides being a renewable and abundant source of energy, it has a high potencial for bioconversion to value-added bioproducts. Among its components, the hemicellulose portions (mainly xylans) represent around 25% to 40% of their composition after cellulose that constitute the main component which represents between 50% and 70% of the total. In adition to the lignin, both the cellulose and hemicellulose, make its structure to be resistant to the enzymatic degradation. Thus, it is necessary the cooperative and synergistic effect of various enzymes, including cellulases and xylanases, to reach higher yields for its degadacion. In the present study Microbacterium sp. AR462-2, a cellulolytic and xylanolytic actinobacteria isolated from intestines of wood beetle larvae, was characterized. The effect of various carbon sources was evaluated on cellulases and xylanases production into Omeliansky mineral culture medium. The substrates assayed as sole carbon source were xylan, lactose, glucose, sucrose, fructose, maltose, carboxymethylcellulose (CMC) and filter paper. This strain was taxonomically identified as a member of Microbacterium spp. according to the sequence analysis of the 16S ribosomal gene. Microscopic observation of AR462-2 strain showed small yellow rods (RAL 1014). Physiological studies showed that this strain did not produce melanic nor soluble pigment. Growth was observed between 5.0 and 8.0 pH units and showed halotolerance and lysozyme resistance. It was able to grow in presence of various carbon sources. M. sp. AR462-2 secreted cellulases when glucose 1% (w/v) was used as a sole carbon source which activity measured was 0.1 U/ml. Also, this strain showed evidence of mild degradation of filter paper in liquid mineral medium. Xylanolytic activities were detected in all culture medias, but the highest xylanase production was recorded when lactose 1% (w/v) was added individually in Omeliansky´s medium. The highest xylanase activity measured was 1.03 U/ml within 7 days using lactose, while in presence of CMC was 1.14 U/ml but after 14 days of culture. Further assays were performed in order to improve both growth and production, by adding casein peptone. Production rates were similar although growth was significatively shortened to 3 days. These results suggest that lactose could be used for enzyme production by Microbacterium sp. AR462-2 as an inexpensive carbon source, since lactic whey is an abundant industrial by-product.