Construction Of The Straw Rapid Degradation Strain System And Its Application In The Treatment Of Organic Pollutants

The rapid degradation of straw can not only solve the problem of environmental pollution which caused by waste of agricultural resources and incineration of straw,but also have important value for improving soil structure and increasing fertility,and have great significance for promoting the healthy development of agricultural ecology.In this paper,the straw rapid degradation strain system(TATS)constructed from recombinant Trichoderma reesei ZJ-09,Aspergillus niger ZU-06,and Trametes versicolor was used to study the degradation of straw.The laccase produced in the solid-state fermentation process was used to catalyze the degradation of several types of typical organic pollutants in the environment,and based on this,a coupling test of degradation of straw and bioremediation of soil pollution by TATS was conducted.Using rice straw as substrates in SSF,it was found that recombinant T.reesei could not only produce cellulose and laccase,but also degrade lignin which could not be used by T.reesei.After 10 days of solid state fermentation,FPA and laccase activity can reach 110.4 IU/g and 24.5 IU/g,respectively.The degradation rates of straw cellulose,hemicellulose,and lignin are 56.1%,49.3%,and 36.8%,respectively.And the weight loss rate reached 41.1%,which increased by 23.9%comparing with the starting strain.The study found:recombinant T.reesei and Bacillus subtilis were not suitable for cooperative fermentation.Adding A.niger as auxiliary strain can effectively increase cellulase and xylanase activities in solid substrates,FPA and ?-glucosidase activity were 132.7 IU/g and 213.1 IU/g respectively and xylanase activity reached 6082.6 IU/g,which increased by 20.2%,1200.1%,and 6.3%comparing with recombinant T.reesei,and the degradation rates of straw cellulose and hemicellulose were increased by 5.5%and 13.3%respectively,the straw weight loss rate increased by 19.5%,but the lignin degradation rate decreased.It was found that T.versicolor can be used as an auxiliary strain to effectively improve the laccase activity in solid matrix,the laccase activity can reach 33.5 IU/g during synergetic fermentation,which is 37.0%higher than recombinant T.reesei,and the lignin degradation effect can increase by 42.9%,but the degradation rate of cellulose and hemicellulose was not significantly improved.Therefore,based on the recombinant T.reesei,adding A.niger and T.versicolor as supplementary strains to complement advantages,the related effects of composition ratio,inoculation time,sequence of different strains in TATS,and the conditions of solid-state fermentation factor were studied.The results showed that according to the growth characteristics of strains in the fermentation substrate,T.versicolor should first be inserted into the fermentation substrate,and the recombinant T.reesei and A.niger should be delayed for 1 day and 2 days,respectively.When the temperature of SSF was 30?,appropriate inoculation ratio was 2:2:1,total inoculation amount was 10%(v/w),amount of bran was 10%(w/w),and the substrate moisture content was 70%,FPA,xylanase,and laccase activities reached 134.7 IU/g,6450.3 IU/g,and 30.4 IU/g,respectively on the 10th day.The degradation rate of straw cellulose,hemicellulose,and lignin can reach 64.2%,61.5%,46.2%,and the weight loss rate of straw is 53.1%.Moreover,during the application of TATS,it was found that it had a good degradation effect on different crop straws.Among them,the highest laccase activity was 27.3 IU/g,52.2 IU/g and 37.8 IU/g when wheat,corn straw and bagasse were used as substrate substrates,the corresponding straw weight loss rates were 42.3%,46.8%and 35.4%,respectively.Using rice straw as substrate to perform a simulated scale-up test on TATS,it was found that the peak of laccase activity reached 12.3 IU/g on the 10th day,FPA peaked at 78.4 IU/g on the 12th day,weight loss rate of straw reached 35.1%with inoculation way of seed broth under natural conditions.Comparing with this,using TATS enzyme koji as inoculation way,the peak of laccase activity reached 16.4 IU/g on the 10th day,FPA and xylanase activity peaked at 96.4 IU/g and 5247.8 IU/g on the 12th day,and the degradation rates of cellulose,hemicellulose,lignin of rice straw reached 42.3%,44.5%,27.2%,respectively.The weight loss rate of straw reached 41.5%.TATS can not only achieve rapid degradation of different crop straws,but also has a good application effect under natural conditions,and can also produce laccase for the degradation of pollutants,which has practical application potential.The veterinary antibiotics chlortetracycline and oxytetracycline were degraded by laccase produced in SSF of TATS.The results showed that at the condition of reaction time 5 h,pH 5.0,60?,and 120 r/min without additional mediators,degradation rate of chlortetracycline can reach 95.7%.In addition,the laccase-syr/van composite natural mediator system was constructed under the conditions of laccase dosage of 0,1 IU/mL,50?,120 r/min,and pH 4.0.After 4 h of reaction,the degradation rate of oxytetracycline was as high as 95.1%.In the experiment of degrading chlorpyrifos by using enzyme koji of TATS,it was found that at the conditions of without additional mediator,the amount of enzyme koji 0.04 g/mL,50?,pH 4.5 and 120 r/min,after 6 h,the degradation rate of chlorpyrifos in water can be up to 95.3%.During the treatment of chlorpyrifos-contaminated soil by enzyme koji,it was found that turning over the pile can accelerate the degradation of chlorpyrifos by enzyme koji but not affect the final degradation rate of chlorpyrifos.Under the condition of enzyme koji was spread on the upper layer of contaminated soil,enzyme koji dosage 10%(w/w,5 moisture content 60%,after 12 days,the degradation rate of chlorpyrifos reached 58.3%.The coupling experiment of TATS degrading straw and chlorpyrifos-contaminated soil bioremediation was performed in a shallow dish in the open environment.The straw substrate was tiled on the upper layer of chlorpyrifos-contaminated soil.Using the inoculation way as simulated scale-up test to inoculate 2%(w/w)enzyme koji,keeping the substrate moisture content 60%,and the action time is 14 days.The results show that the peak of laccase activity reaches 17.4 IU/g after 10 days,and the peak of FPA reaches 92.4 IU/g after 12 days.The degradation rates of straw cellulose,hemicellulose and lignin were 41.2%,45.5%and 26.2%,the weight loss rate of straw was up to 42.4%,and the degradation rate of chlorpyrifos was 53.3%after 14 days.TATS has a good application effect in the treatment of degraded straw and pollutants,and also provides a reference for the degradation of other pollutants.The research results of this paper not only have great significance and promotion value in the utilization of straw resources,but also can produce high yield laccase with a wide range of substrates and environmental friendly characteristics during the degradation of straw.The application value lays the foundation for further upgrading of straw rapid degradation technology and pollutant bioremediation.