| Lignocellulose is most abundant and renewable resources on the earth,and it is important for the degradation and utilization of lignocelluose to control environmental pollution,to develope bioenergy industry and to promote sustainable agriculture.The biodegradation and conversion of lignocelluloses is one of the ways,which lignocellulose can be reused efficiently.For this aim,how to obtain the microorganism capable of lignocelluloses degradation is the first step.In nature,lignocellulose is degraded with the cooperation of many microorganisms,and the research on the function of microbial community is a hotspot in the environmental microbial ecology.A stable microbial community,named WSC-9 with high cellulose-degradation ability,was constructed in our lab.However,the mechanism responsible for the stable coexistence of many species of microorganisms has not yet been clarified.In this experiment,isolates exsiting in the WSC-9 were isolated and characterized,and microbial diversity of WSC-9 was analysed with the methods of plating,anaerobic cultivating and cloning.Then,a new artificial microbial community,also with high capability of cellulose degradation,was reconstructeded with mixing five isolates,and then,the synergic mechanism of cellulose degradation was analysed through knowing isolates out from the new microbial community.1.Five aerobic bacterial strains were isolated by dilution spreading plate process,which named WSC-9-1,WSC-9-2,WSC-9-3,WSC-9-4 and WSC-9-5.And three strictly anaerobic bacterial isolates were isolated under static conditions using Hungate screw-capped test tubes,which were named WSC-9-A,WSC-9-B and WSC-9-C.They were to be identified by 16 S rDNA gene sequence analyses.Eight bacterial strains were belonged to Ureibacillus,Brevibacillus,Clostridium,Pseudomonas and Bacillus.The information and result of T/A clone covered all isolates from plating.2.Five aerobic bacterial strains were noncellulolytic after cellulose-degradation experiment.WSC-9-A and WSC-9-B were strictly anaerobic,thermophilic and cellulolytic bacterium.WSC-9-C was noncellulolytic bacterium.53.8% total weight of rice straw was degraded by WSC-9-B,including 64.3% of cellulose,44.7% of hemicellulose,16.8% of lignin within 10 days at 50 ?(microbial community WSC-9 could degrade 80.9% of rice straw in weight,including 92.1% of cellulose,73.8% of hemicellulose,50.9% of lignin under the same culture conditoins).The optimum temperature and initial pH for its growth and cellulose degradation is 50 ? and 7.0,respectively.The substrates,such as glucose,fructose,ribose,mannose,mannitol,melibiose,lactose,xylan,maltose,saccharose,xylose,cellobiose,cellulose,filter paper and rice straw,were motebalized by WSC9-B.In addition,many kinds of compounds,such as ethanol,acetic acid,propionic acid,butyric acid and so on,were detected by gas chromatoqraphy mass spectrometry(GC/MS)during the cellulose degradarion process.WSC-9-B was straight rods,0.40-0.55 ?m×2.00-3.00 ?m,and spores were oval and subterminal under a scanning electron microscope(SEM).On the basis of 16 S rDNA gene sequence similarity,was mapped to the genus Clostridium.It is closely related to 37-7-2Cl(99%),HAW-RM37-2-B-1600d-W(99%).WSC-9-B was mapped to cluster III of the genus Clostridium.3.A new artificial microbial community,with high capability of cellulose degradation,was reconstructeded with mixing five isolates which were WSC-9-3,WSC-9-5,WSC-9-A,WSC-9-B and WSC-9-C.The results indicated that key cellulolytic bacteria in new microbial community were WSC-9-A and WSC-9-B,and they can decompose lignocellulose to produce ethanol.WSC-9-A was similar to WSC-9-B,instead of cellulose degradation.Meanwhile,WSC-9-3 and WSC-9-5 used production resulted from cellulose-degradation to produce volatile organic acid,and created optimum conditions of cellulose-degradation accordingly.At the same time,WSC-9-C played the role of controlling pH value of ferment system,and could sustain pH at the range from 7.6 to 6.0 during the process of cellulose degradation. |
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