Screening Of Cellulose-producing Microorganisms And Degrading Of Straw

Lignocellulose biomass is considered to be the most abundant renewa ble resources on earth.It has important economic benefits by converting it into biofuels or using it to produce high value-added products.Rational and effective use of crop waste materials such as corn straw can reduce pollution and protect the environment.The cellulose complex enzyme system can hydrolyze lignocellulose efficiently to produce fermentable sugars,thereby producing biofuel ethanol.It plays an important role in the process of biomass production of biofuels because of its mild reaction conditions and non-pollution to the environment.Microorganisms can not only produce cellulase,but also degrade straw efficiently.Therefore,it is an important task to isolate and screen straw-degrading strains capable of producing high-yield intact cellulose complex enzyme system.In this study,we isolated and screened straw-degrading strains which can produce high-yield cellulase,optimized the conditions for enzyme production,determined the optimum conditions for cellulase hydrolysis of strains,salt and ionic liquid resistance,and determined the degradation effect of cellulase on straw pretreated with ionic liquid,an effective way for straw degradation was provided,and salt-tolerant and ionic liquid-tolerant cellulase was obtained.Three strains with high cellulase activity were obtained by collecting soil samples,separating and purifying,primary screening and rescreening.After morphological and molecular biological identification,they were named Penicillium oxalicum HC6,Talaromyces verruculosus SQ6 and Aspergillus terreus SQ7,respectively.The enzyme production conditions of three strains were optimized.Under the optimal fermentation conditions,the three enzyme activities of P.oxalicum HC6 were FPase 0.20 U/m L,CMCase 0.63 U/m L and ?-glucosidase 1.55 U/m L,the three enzyme activities of T.verruculosus SQ6 were FPase 0.26 U/m L,CMCase 0.62 U/m L and ?-glucosidase 1.08 U/m L,the three enzyme activities of A.terreus SQ7 were FPase 0.38 U/m L,CMCase 0.68 U/m L and ?-glucosidase 0.61 U/m L.Moreover,in the range of 0%-5.0% Na Cl(w/v)concentration,the yield of CMCase and ?-glucosidase produced by P.oxalicum HC6 increased and the yield of ?-glucosidase produced by A.terreus SQ7 increased,but the ability of T.verruculosus SQ6 strain to produce enzymes showed a downward trend with the increase of Na Cl concentration.The optimum p H value and temperature of cellulase hydrolysis were determined.The results showed that the optimum p H value of P.oxalicum HC6 cellulase was 5.0,the hydrolysis temperature was 60?,and the enzyme activities were FPase 0.20 U/m L,CMCase 0.71 U/m L and ?-glucosidase 7.44 U/m L,respectively.The optimum p H value of T.verruculosus SQ6 cellulase was 4.0,the hydrolysis temperature was 60?,and the enzyme activities were FPase 0.30 U/m L,CMCase 1.08 U/m L and ?-glucosidase 2.38 U/m L,respectively.The optimum p H value of A.terreus SQ7 cellulase was 5.0,the hydrolysis temperature was 60?,and the enzyme activities were FPase 0.45 U/m L,CMCase 0.96 U/m L and ?-glucosidase 0.99 U/m L,respectively.At the same time,the salt tolerance of cellulase was determined.In the range of 0%-2.5% Na Cl(w/v)concentration,the activities of CMCase and ?-glucosidase produced by P.oxalicum HC6 and the activity of ?-glucosidase produced by T.verruculosus SQ6 increased gradually.In the range of 0%-5.0% Na Cl(w/v)concentration,the FPase activity of A.terreus SQ7 was increased and CMCase was able to maintain 100% enzyme activity at 15.0% Na Cl(w/v).The tolerance of cellulase to ionic liquid was determined.In the range of 0%-2.5% ionic liquid(w/v)concentration,CMCase and ?-glucosidase produced by P.oxalicum HC6 were stable,while FPase and CMCase of A.terreus SQ7 showed an upward trend.The FPase activity of T.verruculosus SQ6 increased in the range of 0%-7.5% ionic liquid(w/v)concentration.The corn straw pretreated with ionic liquid was hydrolyzed by cellulase of strains for 72 h.The hydrolysis of P.oxalicum HC6 cellulase yielded 12.29 mg reducing sugar with a total sugar yield of 24.58%.The hydrolysis of T.verruculosus SQ6 cellulase produced 13.35 mg reducing sugar with a total sugar yield of 26.70%.The hydrolysis of A.terreus SQ7 cellulase yielded 13.01 mg reducing sugar with a total sugar yield of 26.02%.The results showed that the three cellulases could hydrolyze the straw pretreated by ionic liquid effectively to produce fermentable reducing sugar,which could be further used to produce biofuels or other high value-added products,and the use of straw biomass as a cheap substrate could reduce environmental pollution.