Screening And Optimization Of Microbial Communities For Straw Degradation And Diversity Analysis

China is an agricultural country,and the crop straw production is enormous.However,the straw utilization efficiency was very low,and a single strain still cannot significantly improve the degradation efficiency.Therefore,in order to improve the utilization efficiency of straw,the development of microbial systems that can efficiently utilize lignocellulose in straw has become the focus of research.This study was based on different types of media.After long-term restrictive cultivation under continuous shaking culture conditions,three microbial systems with better degradation effects were screened with endonuclease,B-glucosidase,Xylanase,and degradation rate as screening indicators.They are M(straw-degrading composite microbial system),P(straw-degrading mixed microbial system),and C(straw-degrading mixed microbial system),and their degradation rates of rice straw are 43.75%,41.88%,and 39.06%,respectively.The degradation rates of other microbial systems are less than 35%.Based on CMCase and Xylanase's activities,the optimal time for the microbial system's enzyme production was determined.M's optimal enzyme production time was 7 days,P was 9 days,and C was 7 days.The single factor method investigated the liquid volume,fermentation temperature,and carbon source type on the above three microbial systems' fermentation.The DNS method and the weight loss method were used to determine the cellulase activity and strawweight loss rate.The results show that the optimal conditions for the M consortium are:liquid volume of 500 mL Erlenmeyer bottle is 200 mL,the cultivation temperature is 30?,the carbon source is corn stalk,and under this condition,the maximum degradation rate is 45%;the optimal conditions for the P consortium are:liquid volume of 500 mL Erlenmeyer bottle was 200 mL,culture temperature is 38?,the carbon source is rice straw,and degradation rate is 43%;the optimal conditions for the C consortium are:liquid volume of 500 mL triangle bottle is 120 mL,culture temperature is 30?,the carbon source is corn stalk,and degradation rate was 40%.Compared with the non-optimized fermentation conditions,the weight-loss rates of flora M,P,and C consortium on straw increased by 1.25%,1.12%,and 0.94%,respectively.The three strains' degradation effects were analyzed by determining the contents of soluble organic matter(sCOD),total phosphorus,and ammonia nitrogen.The results showed that the sCOD,total phosphorus,and ammonia nitrogen of straws treated with M,P,and C strains increased at the end of fermentation compared with the blank control.The sCOD increased by 33.94%,45.32%,and 57.84%,respectively;total phosphorus content increased by 38.15%,29.69%,and 26.77%,respectively;ammonia nitrogen content increased by 62.98%,62.5%,and 26.68%,respectively,indicating that the degradation effect of M strain is better than that of Flora P and C.High-throughput sequencing technology was used to analyzed the diversity and complexity of the bacteria in the fermentation process.The dominant bacteria of the flora M strain were Stenotrophomonas,and the abundance increased from 23.28%in the early stage of fermentation to 64.36%in the middle stage.The dominant fungus was Meyerozyma,which increased from 17.58%in the early stage to 61.27%in the late stage.Simplicillium,Malassezia,Alternaria were present in the early stage.Sphingobacterium,Penicillium,and Gibberella were dominant in the middle stage.Citricoccus,Meyerozyma,and Verticillium were the primes in the end-stage.The predominant bacteria in the flora P were Bacillus,which increased from 38.08%to 83.18%,and the dominant fungus was Simplicillium,which increased from 6.7%to 47.8%.Sarocladium was leading in the early stage;Gibberella and Pseudeurotium led in the middle stage;Ornithinbacillus showed in the end-stage.The dominant bacteria in flora C were Stenotrophomonas,which increased from 40.66%to 70.71%,and the dominant fungi were Aspergillus,which increased from 48.76%to 84.73%.Pseudomonas and Malassezia were dominant in the early stage;Sphingobacterium and Aspergillus led in the middle stage;Verticillium and Sarocladium led to the end-stage.The experiments have shown that the microbial system composed of bacteria and fungi can promote the degradation of straw,providing theoretical support for the subsequent enzyme purification and further research on the critical bacteria genus and lays a foundation for developing biofuels livestock feed other chemical products.