Screening and enzymatic characterization of the fungal strains producing lignocellulose-degrading enzymes

Abstract:

[Background] Microbial degradation of straw has attracted increasing attention of researchers. [Objective] To screen out the fungal strains with fast growth and strong activities of degrading lignin and cellulose for the efficient utilization of straw. [Methods] The fungal strains were isolated from the samples collected in the natural environments. PDA-guaiacol and PDA-carboxymethylcellulose were used for preliminary screening and then the activities of laccase and carboxymethyl cellulose (CMCase) of the selected strains were determined by liquid fermentation. The target strain was obtained by re-screening based on mycelial growth rate and identified by sequencing of internal transcribed spacer (ITS). Furthermore, the laccase and CMCase activites of the target strain was determined and the enzymatic properties were studied. [Results] A total of 18 strains of fungi were isolated from the samples, among which 9 strains producing lignocellulose-degrading enzymes were selected through preliminary screening. After re-screening, strain M1 with high activities of laccase and CMCase and fast mycelial growth was screened out as the target strain and identified as Pleurotus ostreatus. The strain had the laccase and CMCase activities of (243.59±1.11) U/mL and (36.03±0.63) U/mL, respectively, as well as the mycelial growth rate of (9.43±0.32) mm/d during the 5 days of culture. The relative activity of laccase produced by strain M1 was the most stable at pH 5.5 and over 90% in a pH range of 5.0 to 6.5 and below 55 ℃. The relative activity of CMCase produced by strain M1 was the most stable at pH 6.0 and over 90% in a pH range of 5.5 to 6.5 and below 60 ℃. [Conclusion] P. ostreatus M1 had high laccase and CMCase activities and the potential of degrading lignin and cellulose. This study provides a promising fungal strain for the biodegradation of straw.