The Structural And Functional Contributions Of ?-glucosidase-producing Microbial Communities To Cellulose Degradation In Composting

Compost habitats sustain a vast ensemble of microbes specializing in the degradation of cellulose and are thus important both for their roles in the global carbon cycle and as potential sources of biochemical catalysts for advanced biofuels production.During the whole process of cellulose degradation,due to ?-glucosidases are easily inhibited by the end product feedback(glucose),?-glucosidase has been considered to be the rate limiting enzyme and the bottleneck of effcient degradation of cellulose through enzymatic route.In order to investigate this problem,natural compost and inoculant compost were set up in this experiment.The aim of our study was to investigate the relationship between ?-glucosidase-producing microbial communities and cellulose degradation during cattle manure-rice straw composting.Natural compost and inoculant DN-1 compost were set up in this experiment,the temperature of compost piles and ambient were measured,and the contents of cellulose,hemicellulose and lignin in the compost were measured,in addition,the content of glucose and cellobiose were determined using HPLC,the activities of CMCase and ?-glucosidase were determined;The microbial community composition of produce GH1 and GH3 families ?-glucosidase gene in compost was analyzed by PCR-DGGE;The universal primers and specific primers were designed for q-PCR(Real-time Fluorescent Quantitative PCR)and q-RT-PCR to analysis the changes of the gene copy numbers and the transcription efficiency of GH1 and GH3 families ?-glucosidase gene were detected at the population and individual level in composting.By analyze the correlation of the variations of microbial community succession and the changes in gene copy number of the dominant microbial species with the changes of ?-glucosidase activity,to further reveal the potential relationship of degradation of cellulose-based substance and the variations of microbial species and copy number which have ?-glucosidase function gene.The results of the research are following:Our results confirm that,in general,the thermophilic phase of composting is the main stage of cellulose degradation;during this phase,the cellulose degradation rate and the CMCase and ?-glucosidase activities of inoculant composting were higher than those observed during natural composting.We observed there was approximately 20% of degradable cellulose remaining intact,and significant accumulation of glucose,while the activity of CMCase and ?-glucosidase showed a decreasing trend at later stages of the nature composting.Gene expression analysis showed that the bacterial GH1 family ?-glucosidase genes make greater contribution in cellulose degradation at the later thermophilic stage in inoculant compost.In this study,we showed that functional genes with high abundance but low transcription efficiency can play a greater role in cellulose degradation than genes with high transcription efficiency and low abundance.High cellobiose concentrations might have efficiently induced the transcription of functional genes that contribute to the composting process.At sufficiently high glucose concentrations,the functional microbial community in compost is altered,which may contribute to maintaining ?-glucosidase activity despite the high glucose content.These results provide an efficient approach to more efficiently degrade cellulose in compost,thereby enhancing the activity of ?-glucosidase by promoting ?-glucosidase-encoding genes expression.