Lignin biodegradation by thermomyces lanuginosus EFB2 and aspergillus flavus EFB4 co-culture and pure culture in solid state fermentation

Abstract

The performance of pure culture and co-culture of T. lanuginosus EFB2 and A. flavus EFB4 in lignin biodegradation were observed in solid state fermentation (SSF) using oil palm empty fruit bunch (OPEFB) as the substrate. Biodegradation of lignin was evaluated based on the activity of crude ligninolytic enzymes (LiP, MnP and Lac), FPase assay and fibre content analysis of OPEFB through gravimetric method after SSF. Results showed that EFB2, EFB4 and EFB2+EFB4 were able to produce all major ligninolytic enzymes showing the ability of both strains to grow and degrade the OPEFB in SSF. Higher activity of MnP (27.17 U/L) and Lac (2.81 U/L) in EFB2+EFB4 compared to EFB2 (5.41 U/L and 2.20 U/L) and EFB4 (22.2 U/L and 2.37 U/L) pure culture demonstrated that co-culture may degrade lignin better than pure culture. MnP was predominant in both fungi as shown by the highest activity produced (27.17 U/L) among all of the lignolytic enzymes. As a pure culture, EFB4 produced significantly higher activity of LiP, MnP and Lac than EFB2. A very low level of FPase activity was detected in all cultures throughout the SSF period. The evaluation of the fibre content in OPEFB showed that EFB2, EFB4, and EFB2+EFB4 caused significant decrease of lignin, cellulose and hemicellulose amount after SSF. A maximum loss of lignin at 7.3 % was recorded on the day 8 of SSF by EFB2+EFB4. Low level of correlation between ligninolytic enzymes activity and the decrease of lignin content was observed. Characterization of LiP, MnP and Lac demonstrated that they were stable at acidic condition and LiP and MnP exhibited optimum activity at pH 4 - 5, while Lac at pH 3. Optimum temperature for LiP and MnP were recorded at 60ºC and they were stable at 30ºC-50ºC over 3 hours of incubation while optimum temperature of Lac is 70ºC and stable at 30 - 60ºC. Results suggest that co-culture of EFB2 and EFB4 in SSF effectively improved lignin biodegradation in OPEFB.