Isolation and Screening of Potential Lignocellulolytic Microorganisms from Rubber Bark and Other Agricultural Residues

Abstract

Lignocellulolytic microorganisms were isolated from cow manure, the soil from naturally grown bamboo, the piles of rubber bark and the composting piles. The samples were collected at 9 different locations which were 5 cm deep from the surface. The basal medium (BM) containing CMC (carboxymethyl cellulose) or xylan as a carbon source and the lignin modifying basal medium (LBM) with ABTS {2,2¢-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid} or DMP (2,6-dimethoxyphenol) as an inducer were used for the primary screening of microorganisms producing cellulase, xylanase, laccase and manganese peroxidase, respectively. Forty-five bacterial isolates (B), twenty-five isolates of actinomyces (A) and fifteen fungal isolates (F) were obtained. After that twelve isolates were selected to evaluate enzyme production in LBM containing decomposed rubber bark as a carbon source at 30 °C and at 45 °C under aerobic conditions (150 rpm shaking). The isolates F6, A2 and B15 displayed the highest enzyme activities with a CMCase activity of 0.61, 0.33 and 0.21 U/mL, respectively. Moreover, they also produced xylanase with an activity of 0.61, 0.36 and 0.32 U/mL, respectively. However, only the isolate F6 showed laccase activity and manganese peroxidase activity of 0.81 and 0.56 U/mL, respectively. The isolates B15 and A2 were identified by 16S rDNA with 99 % similarity to Bacillus subtilis and Streptomyces thermovulgaris , respectively. Aside from that, isolate F6 was identified by 18S rDNA with 100 % similarity to Trichoderma asperellum . When these microorganisms were grown in the LBM broth with 10 % decomposed rubber bark they produced the highest lignocellulolytic enzymes in the stationary phase of growth.