Metagenomics Study On Lignocellulose Breakdown And Its Key Functional Enzymes Genes Regulated By Illite/Smectite Clay In Composting

Composting is a biotechnology that can reuse organic solid waste after harmless treatment by microorganisms.However,the performance of traditional compost in lignocellulose degradation is poor,so it is very necessary to solve this issue.As a kind of layered clay mineral with large specific area and porosity,excellent structure of illite/smectite clay is conducive to the improvement of the microenvironment,the survival and growth of microbes in the process of composting.However,little is known about whether I/S can optimize composting habitats and promote lignocellulose breakdown and humification.In view of the scientific question of whether I/S can optimize composting habitat and promote lignocellulose degradation and humus process,this paper studied the effects of I/S on lignocellulose degradation especially the degradation of lignin,auxiliary activities(AAs)abundances associated with lignin degradation and humification process in composting.With the further study,the occurrence and evolution charactersistics of Lytic polysaccharide monooxygenases(LPMOs)in composting and its potential synergistic effect on cellulose degradation were explored.In addition,the effects of mature compost product on crop growth were also discussed.The main results of this paper are as follows:(1)The test group(TG)with 10% I/S and the reference group(RG)were established.The results indicated that the addition of I/S made the degradation rate of cellulose,hemicellulose and lignin in TG(1.56 %,29.01 %,19.95 %)was higher than that in RG(1.16 %,17.24 % and 13.14 %).The microbial community in TG changed observably,in which the relative abundance of Actinobacteria increased and Proteobacteria decreased.Compared with RG,the abundance values of AA2,AA10,GH1 and GH10 in TG increased by 15.18 %,29.28 %,31.08 % and 21.65 %,respectively.Redundancy analysis(RDA)showed that the temperature was positively correlated with the abundance of AA2,AA10,GH1 and GH10,whereas with the organic matter(OM)content was negatively correlated.Overall,adding I/S to the composting could stimulate microbial activity,promote the degradation of lignocellulose.(2)The abundances of AA1,AA2 and AA3 in TG were 28.98 %,15.18 %and 14.36 % higher than that in RG,respectively.Meanwhile,I/S greatly boosted the efficiency of lignin degradation(17.96 %)and humus formation(7.16 %)compared with RG(13.10 %,3.49 %).Furthermore,Actinobacteria was the microorganism with the greatest contribution in RG and TG to secreting AA1(41.12 %,57.37 %),AA2(62.42 %,65.28 %),AA3(47.04 %,55.47 %)based on metagenomics.RDA demonstrated that I/S could make the laccase encoding gene-AA1 contribute more to HS formation relative to AA2 and AA3.In conclusion,applying I/S in dairy manure composting effectively improved the abundance,bioavailability of lignin degradation functional gene enzymes and humification process.(3)Metagenomics analysis were used and found that AA9,AA10,AA11 and AA13 were found in the composting where AA9 and AA10 were present in the whole composting process and AA10(8258)abundance was the highest.Furthermore,synergies between LPMO and cellulases(GH5,GH6,GH9,GH48 and CBM2),auxiliary activities(AA3,AA4,AA5,AA7 and AA12)that fuel LPMO reactions were discussed.According to species contribution,Actinobacteria and Ascomycota were respectively the dominant microbes producing AA10 and AA9,accounting for more than 80 % of the total relative abundance.RDA demonstrated that AA9 had the greatest effect on promoting organic matter(OM)degradation and AA10 had the greatest effect on improving compost quality.(4)Mature compost products were applied to cultivate cabbage growth instead of conventional compound fertilizer.After observation,it was found that cabbage with compost products grew better than that without compost products,especially the compost products with illite/smectite clay.In addition,the cost and industrialization of composting were also analyzed.To sum up,this study introduced illite/smectite clay as a conditioner into composting and provided a new idea for improving composting microenvironment and promoting the lignocellulose degradation and humification process during composting by metagenomics technology.Meanwhile,the occurrence,distribution and succession of LPMOs in dairy manure-bagasse pith composting were also found,which provided new sights for future research on LPMOs in composting process.