Effects Of Physico-chemical Parameters On The Glycoside Hydrolase Family 6 Genes During Composting Of Agricultural Waste

Cellulose is the most abundant renewable carbon source in the nature with an annual output more than 150 billion tons and widely exists in agriculture and forestry organic waste and so on,especially in agriculture organic waste.Only in China,the annual output of crops straw is as high as 700 million tons and the output of rice straw is the largest among them.As one of the biodegradation technology,composting is often used to transform agricultural organic waste into stable usable resources under controlled conditions.It is an aerobic and spontaneous heating process of recycling organic waste,which is controlled by microbial communities.The microbes contain GH6 family gene are the primary microorganisms which are involved in the early stage of cellulose degradation during composting.The metabolism microbes which contain GH6 family genes are important for the utilization of composting.Rice straw was used for aerobic composting.The denaturing gradient gel electrophoresis of polymerase chain reaction(PCR-DGGE)was used to study the changes of glycoside hydrolase family 6(GH6 family)genes during composting of agricultural waste.Redundancy Analysis(RDA)and Monte Carlo permutation test were applied to determine the relationships between the change of GH6 family genes and eight physico-chemical parameters.The results of composting showed that pH increased obviously during first 4 days and reached the highest value 8.96 on day 4.C/N ratio decreased gradually during the whole process from 30.19 to 17.72 and it conformed to the maturity condition of C/N ratio.Pile temperature increased rapidly to peak value 61.4? on day 2 and maintained above 50? for 6 days,it is long enough to suppress pathogenic microorganism.WSC(Water soluble carbohydrates)decreased during the first 4 days,and then increased during day 4 to day 8,after that,WSC decreased gradually to 1.48 mg.kg-1.TOM(total organic matters)decreased gradually from 447.75 g.kg-1 to 308.6 g.kg-1.The content of TN(total nitrogen)increased gradually.The results of PCR-DGGE showed that the diversity of GH6 family genes was decreased and the abundance of the genes showed a dynamic change trend due to the change of the dominant bacteria.The species of microbeswere in the early stage of composting were significantly more than the later-stage of composting.The dominant bacteria numbered with 24 and 25 were appeared predominantly at thermophilic and maturity period during the composting,and the dominant bacteria of two period were different.The results of RDA and Monte Carlo permutation test suggested that pH,pile temperature,and TN(total nitrogen)had the most significant impacts on the changes of the GH6 family genes(P<0.05),they explained 24.92%?15.57%and 15.04%variation of GH6 family genes during composting.The t-value biplots based on RDA showed that the different microbes had different preference of environmental factors.Based on the different positive or negative correlation between microbes and environmental factors,the microbes could be divided into five grades,number 4-10,number 11-14,number 15-19,number 20-23 and number 24-27.