Effects Of Streptomyces Coelicolor On The Degradation Of Corn Straw By Pleurotus Ostreatus And Its Mechanism

The white-rot fungi Pleurotus ostreatus has great potential in decomposing lignocellulose.At the meanwhile,some bacteria also has the ability to metabolize lignocellulose.In nature,white-rot fungi involved in the process of lignocellulose degradation always co-exist with bacteria and other microorganisms.However,little is known about whether the co-cultivation of bacteria with lignocellulose metabolism ability can further increase the degradation efficiency of lignocellulose by P.ostreatus.BP3 In order to explore the effect of lignin-degrading bacteria on the degradation of lignocellulose by white-rot fungi,four bacteria with lignin metabolism ability were co-cultivated with P.ostreatus BP3 to evaluate their effect on P.ostreatus degrading corn straw,and further study the molecular mechanism from enzymology and transcriptome level.The results are as follows:1.Four different bacteria and the white-rot fungi P.ostreatus BP3 were co-inoculated on solid straw.The results showed that except for Streptomyces coelicolor M145,other bacteria inhibited the growth of P.ostreatus BP3.At the same time,lignin degrading enzyme activities of the four co-cultivation systems were detected,the results showed that S.coelicolor M145,Rhodococcus opacus PD630 and Ralstonia Eutropha H16 can promote P.ostreatus BP3 to secret extracellular laccase and manganese peroxidase.Among them,S.coelicolor M145 can significantly promote P.ostreatus BP3 to secret laccase and manganese peroxidase,which was increased by 105% and 43%respectively compared with P.ostreatus BP3 cultured alone.2.In order to further study the effect of S.coelicolor M145 on the degradation of lignocellulose by P.ostreatus BP3,the different inoculation ratios of S.coelicolor M145 and P.ostreatus BP3 on solid straw substrate were investigated.The results showed that.P.ostreatus BP3 could grow under the initial inoculation ratio of 1:10,1:25 and 1:50.Therefore,S.coelicolor M145 and P.ostreatus BP3 with initial inoculation ratios of 1:10,1:25,and 1:50 were used to ferment corn straw,and the degradation of different components of lignocellulose was analyzed.The results showed that they had different degradation efficiency of lignocellulose.When the initial inoculation ratio was 1:25 and1:50,S.coelicolor M145 can significantly promote the degradation of straw lignocellulose.After 30 days of fermentation,the degradation rate of lignin was increased by 23.93% and18.48% respectively,and the degradation efficiency of cellulose was increased by 30.77%and 31.49% respectively.The addition of S.coelicolor M145 promoted P.ostreatus BP3 to secrete lignin degrading enzymes,including laccase,manganese peroxidase and iron-reduction ability.When the initial inoculation ratios were 1:25 and 1:50,the laccase secreted by P.ostreatus BP3 reached the highest enzyme activity on the 5th day of fermentation.The laccase activity was increased by 61.52% in co-culture of 1:50 initial inoculation ratio,compared with P.ostreatus BP3 culture alone,and the manganese peroxidase and filter paper activity(FPA)reached the highest enzyme activity on the 15 th day of fermentation,FPA was increased by 20.71%.Iron-reduction ability reached the maximum on the 10 th day of fermentation,and increased by 52.86%.The manganese peroxidase activity was increased by 79.52% under the initial inoculation ratio of 1:25,compared with P.ostreatus BP3 culture alone,and FPA reached the maximum on day 15.3.In order to further analyze the molecular mechanism of S coelicolor M145 on promoting the degradation of straw lignocellulose by P.ostreatus BP3,transcriptomes of P ostreatus BP3 singular culture and the co-culture of S.coelicolor M145 and P.ostreatus BP3 with 1:50 of inoculation ratios were analyzed.The results showed that differentially expressed genes were mainly enriched in the KEGG pathway related to carbohydrate degradation and energy metabolism,including carbohydrate metabolism,energy metabolism,and xenobiotics biodegradation and metabolism,as well as regulating peptide and protein release.And the GO terms of peptide and protein release in biological processes were GO:0002790 and GO:0009306 respectively.By analyzing the differential expression of carbohydrate enzymes of P.ostreatus BP3 under different conditions,it can be seen that S.coelicolor M145 can promote the up-regulation of the expression of lignin degradation-related enzymes,such as laccase,manganese peroxidase.At the meanwhile,the expression of some key cellulose-related and hemicellulose-related genes were also increased.Among them,the main enzymes involved in lignocellulose degradation,novel.8353.2 of laccase gene and novel.7030.1 of manganese peroxidase gene were up-regulated by 3.62 times and 20.03 times,respectively.The LPMO gene novel.7656.2involved in polysaccharide degradation were up-regulated by up 238.86 times,and the xyloglucanase gene novel.9583.1 involved in cellulose degradation were up-regulated by up 22.01 times,and the up-regulation factor of genes related to hemicellulose degradation was by up 48.84 times.In summary,we demonstrate that S.coelicolor M145 mainly promoted the expression of key enzymes and relevant genes in P.ostreatus BP3 for lignocellulose degradation,thereby enchancing the degradation of corn straw lignocellulose by this white-rot fungi.