Study On The Degradation Of Corn Stalk By Various Microorganisms

This paper aimed at improving the degradation rate of corn stalks by efficiently degrading the microbes of cellulose and degrading lignin.In this paper,one major strain and two alternatives were screened from eight highly degradable cellulose strains stored in the Bioengineering Laboratory of Shanxi Agricultural University,and screened one auxiliary strain which can make a synergistic effect with the main strain to produce a complete cellulase,thus constructed into mixed strains.Then followed by the optimization of fermentation conditions and medium of the mixed strains.Finally,because of the highest growth rate and highest degradation rate on the pretreatment of corn stalks,Phanerochaete chrysosporium was selected from five kinds of white rot fungi to pretreat the stalks.The degradation rate of corn stalks was treated with the co-culture of mixed strains and the selected white rot fungi,laying the foundation for the application of straw.The main findings are as follows:(1)Study on the peak and occurrence of peak of three kinds of cellulose components and the activity of filter paper enzyme in 10 days of eight highly productive cellulase strains,which including two strains of Trichoderma reesei(Trichoderma reesei and Trichoderma viride),three Aspergillus niger(Aspergillus niger Y8,Aspergillus niger Y9,Aspergillus niger Y14)and three Bacillus subtilis(Bacillus subtilis S1,Bacillus subtilis S2,Bacillus subtilis S3).In general,the ?-GA/FPA ratio of Trichoderma and Bacillus subtilis was in the range of 0.12?1.50,and the ratio of Aspergillus niger was greater than the maximum 1.50.Among them the peak of each enzyme activity of Trichoderma reesei was higher than that of Trichoderma viride,and four emergence times was consistent.The four enzyme activities of Aspergillus niger Y9 were significantly higher than the other two Aspergillus niger,Bacillus subtilis S3's peak is slightly higher than the other two strains,and the occurrence times of peak were more consistent.Therefore,Trichoderma reesei was screened as the main fermentation strain in the mixed strain,Aspergillus niger Y9 and Bacillus subtilis S3 were the alternatives.(2)The three strains were screened by fermented corn stalks to establish the mixed strains:Trichoderma reesei and Bacillus subtilis S3.Then the inoculation sequence and the inoculation ratio of the mixed strains were studied.When the total inoculation amount was constant,Trichoderma reesei and Bacillus subtilis S3 simultaneously were inoculated to the medium and the inoculation ratio was 1:1.(3)With fermentation temperature,fermentation time and total inoculation amount as the independent variable,reducing sugar content as the dependent variable,the response surface test of the optimization of mixed strains fermentation conditions was conducted.The result of optimum fermentation conditions were as follows:fermentation temperature 30.14 ? fermentation time 5.4 d and total inoculation amount of mixed bacteria were 8.34 mL,and the reducing sugar content of maize straw was 260.661?mol/100mL.It can be seen that the corn straw can be effectively improved by mixed microorganisms in liquid,was 1.10 times higher than before.(4)Through a single factor test,four factors were screened and then optimized for the medium by response surface test from one supplemental carbon source(bran),five nitrogen sources(yeast extract,yeast powder,peptone,tryptone and urea)two kinds of nutrient(sodium chloride and potassium dihydrogen phosphate)and growth factor ascorbic acid.The results showed that the medium was consist of corn stalks as sole carbon source,the yeast powder as sole nitrogen source,sodium chloride and potassium dihydrogen phosphate as the nutrient salt and ascorbic acid as the growth factor.And the formulation of optimum culture was as follows:carbon and nitrogen ratio 7.11:1,sodium chloride 0.61%,potassium dihydrogen phosphate 0.1525%and ascorbic acid 0.0528%,was 1.98 times higher than the above study.(5)In order to further improve the degradation efficiency of corn stalks,in this chapter,with the gro wth rate and the degradation rate of corn stalk as index,lignin were degraded by five kinds of white rot fungi,which were Phanerochaete chrysosporium,Pleurotus ostreatus,Pleurotus ostreatus,Lentinus edodes and Pleurotus eryngii.The higher of growth rate and the degradation rate,the greater the chance of to co-culture with the mixed strains of degrading cellulose.Phanerochaete chrysosporium was screened to be the pretreatment microorganisms,and then mixed with the mixed strain to degrade the corn stalks.Results showed that when the inoculation amount of Phanerochaete chrysosporium was 9 pieces,and the pretreatment time was 15 days,the degradation rate of corn stalks reached to 40.2%.