The Construction Of Co-culture System For Producing Xylanase And Optimization Of Conditions For The Fermentation Of Recycling Potato Pulp

The subsequent treatment and application of by-products from the potato starch processing industry has been a serious problem.The main reason is that the non-degradable components such as cellulose and hemicellulose in them cannot be fully utilized,and the drying and utilization cost is too high,resulting in serious direct environmental pollution caused by direct large-scale discharge.Xylanase is the main enzyme system that degrades hemicellulose.Currently,it is an economical and kind environmental method that using co-culture system to ferment potato pulp.It can not only increase the utilization efficiency of potato pulp and decrease environmental pollution but also obtain extreme useful product like xylanase.Therefore,it is a valuable and widespread biotechnology by applying microbial fermentation in potato pulp treatment.This research screened two strains from soil,which have higher ability to produce xylanase,then constructed co-culture system for producing xylanase and degrading hemicellulose by using of potato pulp.First,eight fungi strains and sixteen Streptomyces strains were screened by repeated plate streaking on the plate by only uses xylan as carbon resource.Then,two-step rescreening was carried out,including choosing higher ability of producing xylanase according to their ration of the trains parent circle's diameter to the colony's diameter as first step and determining the xylanase of the twenty-four strains above by DNS method as subsequent step.Finally,strain J-519 and W-41 were screened and were used to construct co-culture system.By identifying them in both morphological and molecular biology aspects,including observing microstructure of stains,sequencing the ITS sequence of strain J-519 and the 16S rRNA sequence of strain W-41,the polygenetic tree of J-519 and W-41 were constructed by Neighbor-Joining method using Mega 7.0 software.At last,their genus were determined Determining the two genus of them.Constructing co-culture system of J-519 and W-41:the ratio of the J-519 vs W-41was 6:4.J-519 was added after 12 h fermentation of W-41.The enzymatic properties were studied,the optimum temperature is 60?,and xylanase is stable in the range of 20?-65?.The optimum pH is 5.5,and xylanase is stable between pH4.0 and pH 8.0,the relative enzyme activity maintained above 79%.The activity of xylanase can be inhibited by Li⁺?Mg²⁺?SDS,but Cu²⁺?Co²⁺?Fe³⁺and EDTA increased the activity.After carrying out the Single Factor Experiment,Orthogonal test was designed,The optimized conditions got:inoculum size 0.5%,fermentation temperature 28?,fermentation time 120 h,pH7.0.The results showed xylanase activity is 550.39 U/mL,which is 67.88%higher than before,the degradation rates of hemicellulose and COD were test in initial and optimized condition respectively,and they show the two latter are 2.25 and 2.27 times of the two former.Therefore,the co-culture system has excellent optimization affect.