Isolation Of Straw-degradating Microorganisms From Crop Straw Composting And Characterization Of Their Straw Degradation Efficacy

Every year about 8 billion tons agricultural straw wastes including rice straw,wheat straw and corn straw are produced in China.One third of straw wastes is disposed and burned,which causes resources waste and environmental pollution,especially serious damage to the soil ecology and environment.Because of the complex structure of lignocellulose,the decomposting process is very slow.Therefore,development of efficient straw degradation microorganisms that could work well both at normal and high temperature are very important.In this thesis,different heat-resistance strains were screened from a straw composting pile,with which the effect of the composite strains on degradation efficacy was studied in a rice straw liquid fermentation.A factorial design experiment method was used to study the effect of fermentation factors,and the results obtained are as follows:Firstly,10 degradation strains were isolated by using mixture of maize straw,rice straw and selengensis straw as the sole carbon source from the straw composting samples.On the basis of the morphological,physiological,biochemical and molecular identification methods,the mesophilic bacterial strains X301,X302,and X303 were identified as Serratia marcescens,Staphylococcus aureus,and Bacillus subtilis,respectively;the thermophilic bacterial strains X501,X502,and Xy were identified as Bacillus subtilis,Bacillus subtilis,and Bacillus methylotrophicus,respectively;the mesophilic fungal strains Z3-1,Z3-2,and Z3 were identified as Trichoderma viride,Aspergillus fumigatus,and Penicillium oxalate,respectively,the thermophilic fungal strain Z501 was identified as Aspergillus fumigatus.The results from the liquid fermentation show that fungal strains are more efficient in straw degradation than the bacterial strains.Secondly,compared with monoculture,microbial consortia can improve the rice straw degradation efficacy and the loss rate of lignocellulose,especially the cellulose and hemicellulose.The best lignocellulose degradation rate is obtained in the combination of mesophilic fungi Z3-1?Z3-2?Z3 and thermophilic fungi Z501,the effect of lignocellulose total loss during the 7 d and 30? liquid fermentation was more than 32%,up 200%compared with CK,up 146.2%with individual bacteria treatment,up 77.8%with bacteria and bacteria combination,up 42.2%with individual fungi treatment,up 14.3%with bacteria and fungi combination.Thirdly,A 24 experiment model equation[Y=0.46+(0.08/2)X1+(0.11/2)X4+(0.03/2)X1X3;where,Y:straw absolute degradation rate;Xi:single impact factor assignment,(i=1,2,3,4)]was built to describe the effect of time,temperature and microbial consortia on the degradation efficacy.According to the model equation,temperature and time is more important effect on the degradation of rice straw,and the interaction between the environment temperature and lignocellulose degradation strains on the degradation of rice straw is also important.Finally,with the microbial consortia in the liquid fermentation condition of temperature 50?,the degradation time of 7 d,the absolute of rice straw degradation rate was 46.5%,the 15 d absolute degradation rate of rice straw is 57.25%.After liquid fermentation,the straw surface structure was broken,straw damage was serious without organization arrangement.