Construction Of High Efficiency Straw Degrading Complex Bacterial System And Study On Its Degradation Effects

China is a large agricultural country,rich in crop straw resources,but the comprehensive utilization rate of straw is low,and the environmental problems caused by the massive accumulation or burning of straw are becoming more and more significant.In situ rapid return of straw to the field is an important initiative for the comprehensive utilization of straw resources,through the rapid degradation of straw by microorganisms,can increase the types and numbers of microorganisms in the soil,prevent and control pests and diseases,and the straw itself returns nutrients to the soil and improves soil fertility.Therefore,it is important to screen high-efficiency straw-degrading bacteria to promote the in situ return of straw to the soil.In this paper,we screened and identified straw-degrading bacteria,and constructed straw-degrading complex bacterial lines,determined the optimum enzyme-producing conditions of the complex bacterial lines,and studied the degradation effect of high-efficiency straw-degrading bacterial lines on different straws.The main research results are as follows.(1)Four strains with straw degradation ability were obtained by Congo red primary screening and potato straw liquid fermentation test.At 35 d of fermentation,all four strains TXB2,WXB10,HXB11 and HXB17 were able to degrade potato straw with 55.48%,57.73%,55.44% and 54.13% weight loss,respectively;all four strains had endo-β-1,4-glucanase,exo-β-1,4-glucanase,β-glucosidase and hemicellulase activities.within 5d of fermentation;and the maximum endo-β-1,4-glucanase,exo-β-1,4-glucanase,β-glucosidase and hemicellulase activities of strain HXB11 were 383.20U/m L,528.99U/m L,5.62U/m L and 20.60U/m L;strain WXB10 had the highest endo-β-1,4-glucanase,exo-β-1,4-glucanase,β-glucosidase,and hemicellulase activities were238.75U/m L,478.48U/m L,4.82U/m L,and 32.17U/m L;strain TXB2 had the highest endo-β-1,4-glucanase,exo-β-1,4-glucanase,β-glucosidase and hemicellulase activities were 289.93U/m L,533.7U/m L,4.78U/m L and 29.94U/m L;the highest endo-β-1,4-glucanase,exo-β-1,4-glucanase,β-glucosidase and hemicellulase activities of strain HXB17 were 302.05U/m L,509.46U/m L,5.41U/m L and 31.43U/m L,respectively.(2)The four screened strains were identified as Bacillus subtilis(TXB2),B.safensis (HXB11),B.velezensis(WXB10),and B.pumilus(HXB17).(3)The fermentation effect of strains TXB2 and WXB10 in the ratio of 5:4 by volume was investigated by compounding strains TW,HXB11 and HXB17 in the ratio of 6:3 by volume form HH.The results showed that by optimizing the fermentation conditions of the complex strain,the endo-β-1,4-glucanase,exo-β-1,4-glucanase,β-glucosidase and hemicellulase activities of the complex strain TW appeared to be maximum at 25℃,p H 6,with cottonseed sugar and peptone as the only carbon and nitrogen sources,and increased by 61%,30%,77% and 77% compared with the single strains TXB2 and WXB10,respectively.The endo-β-1,4-glucanase,exo-β-1,4-glucanase,β-glucosidase and hemicellulase activities of the complex strain HH showed maximum values at 30°C,p H 7,with mannitol and peptone as the only carbon and nitrogen sources,and increased by 18%,39%,74% and 41% compared to the single strains HXB11 and HXB17.(4)The single strains TXB2,WXB10,HXB11 and HXB17 as well as the complex strains TW and HH all degraded potato,oat,wheat,buckwheat,quinoa and corn straws.After 30 d treatment,the degradation rate of potato straw was 60.08% and 57.24% for TW and HH,59.56% and 52.12% for oat straw,50.32% and 47.64% for wheat straw,53.88%and 48.04% for buckwheat straw,34.16% and 43.16% for quinoa straw,respectively.The degradation rates were 34.16% and 43.04% for quinoa straw,31.56% and 45.64% for corn straw,and the degradation rates of sunflower straw were lower for the two composite strains and four single strains.