| The fungus from soil and humus sample from Eucomia ulmoides forest were screened after multiple rounds of enrichment culture on Eucommia ulmoides bark. Then predominant strain was isolated. The strains'fermentation properties index and comprehensive selection index are determined and evaluated to screen superior strains to extract gutta-percha from the bark of Eucommia ulmoides Oliv. by microbial fermentation. Then predominant strain was identificated and and the fermentation conditions of predominant strain was optimizated. Simultaneously, the study on mechanism of cellulose enzyme solution was carried out. This study aimed to provide predominant strain and theoretical basis for the application of extraction gutta percha by microbial fermentation.The main results showed:(1)27 fungi and 18 bacteria that could grow well on Eucommia ulmoides bark were achieved by enrichment and isolation. Among these strains, fungi P-24, MT-6,MT-4,P-22 and bacteria X-8,X-47,X-32 could be used to extract gutta-percha from the bark of Eucommia ulmoides Oliv.by microbial fermentation. The four fermentation performance indices (fermentation degradability rate, fermentation removal rate, gutta-percha content of surplus, yield rate of Gutta-percha and fermentation loss rat ) of fungi were higher than those bacteria. With good and stable performance on fermentation performance index in the verification test, strain P-24 and MT-6 can be served as high capability strains. According to Morphological specificity and molecular identification, it was confirmed that the strain P-24 belongs to Penicillium oxalicum and the strain MT-6 belongs to Aspergillus niger。(2)Several fermentation experiments showed that strain P-24 has sevseal advantages, such as stronger capacity to degrade the bark of Eucommia ulmoides Oliv., short fermentation period, high yield rate of gtta-percha. After 12-day fermentation, fermentation remove rate of strain P-24 was 72.73%.(3)These factors (including fermentation time, medium moisture, initial pH and fermentation temperature) all have significant positive effects on the degradation of Eucommia ulmoides bark.The optimization experiments of fermentation condition showed: The optimal conditions of strain P-24 for fermentation may get when the medium moisture content was 67.7%, initial pH was 7.0, fermentation temperature was (30±1)℃, fermentation time was 12 d.Trough the model of fermentation removal rate to optimize formula of medium estimated that, a maximal fermentation remove rate(94.22%) could be obtained when the concentration of corn flour, ammonium nitratr and medium moisture were set at 0.50%,1.00%,67.80%, respectively. Simultaneously, the enzyme activity of the carboxymethyl cellulose(CMC)and pectinase were2.9788 and 5.1145μmol/(min?g), respectively. The enzyme activity of CMC and pectinase increased 1.3385 and 2.7742μmol/(min?g), respectively. The result showed a well effected optimization.(4)Comprehensive selection index is applied well in strain screening for extract gutta-percha by microbial fermentation. Evaluation strain with comprehensive selection index not only could avoid missing some predominant strain, but also could reflect the fermentation performance of strain comprehensively. Appliation of cmprehensive selection index to screen predominant strain was simple and practical.(5)During fermentation the enzyme activity of the carboxymethyl cellulose(CMC)and pectinase closely correlate to fermentation removal rate. It is confirmed that dtermination of enzyme activity of CMC and pectinase can be used to assess the fermentation performance of strain. Different strains produced different enzyme, so the degradation is different. It was found that some strains can yield special enzyme to degrade gutta-percha, such as strain F-4,P-47,XT-3,XT-12 with strong decomposition on gutta-percha.So they are not suitable for production strain. The degradation on gutta-percha has no relation with cellulose degradation of strains. |
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