Screening Microbial Strains For Lignin Degradation And Optimizing The Fermentation Condition Of Maize Stover By Multi-strains

Maize stover is an abundant kind of recycled biomass. Its interests lie in lower cost, huge harvest yield, and rich nutrition value. However, the utilization of maize stover is low, attributed to its complicated chemical structure. As the devolpment of microbiologic fermentation technique, it is possible to use it as a kind of roughage for feeding ruminant by biologically transforming, to boarden feedstuff source and to raise its quality. It will bring great benefit for the development of agriculture and animal husbandry in China.The study mainly used maize stover as substrate, screened the strains that have the capacity to degrade lignin from the surface of maize stover and chose representative B7 and F8 as subjects. As laccase was the key enzyme to lignin degradation, experiments on optimizing culture condition of producing laccase were performed by Pleurotus ostreatus and Pleurotus cirinopileatus Sing. Then, we used the screened strains and these two white-rot fungus to ferment maize stover, subsequently optimized the conditions of maize stover degradation. Furthermore, it showed the effects of interaction among tested srtains on producing laccase by the way of solid state fermentation and the change of maize stover composition under different strategies on srtain combination.The meaning of the research lay in finding out there were microbes or not which could degrade lignin origined from maize stover surface, working on getting to know the character of unique microorganisms so as to know more about microbes that exist on the surface of maize stover. The uppermost was to make lignin degradation feasible by micro-fermentation. The test focused on optimizing several fermentation variables to enhance laccase activity and degradation of maize stover by test strains, during the same course, it was useful of providing some kinds of superior strains and processing strategies that can enhance lignin degradation. The realization of lignin bio-degradation means more chances for development of feed industry. So long as to solve the problem of raw and processed materials, it would provide more important basis and valuable experiences for accelerating the agricultural transformation.1,Based on the quo of lignin micro-degradation, and also consulted some screening methods, we put a strategy that screen microorganisms which have the capacity of lignin degradation from maize stover directly forward. These microbes were origined form maize stover surface, used maize stover as nutrition source all that made test more targeting, to be more worthy of studying.2,Research on analyzing of sorts ligninolytic enzymes that produced by tsted strains and the time span of enzyme production. It showed that B7 and F8 began to produce laccase at 30h and 50h respectively; B7 produced Lip and Mnp much earlier, within 11h. The shorten of laccase- producing time made the fermentation cycle shorten in favor of B7 and F8 becoming promising industrial strains to increase the economical benefit.3,The optimizing test carried on at the same time to enhance laccase activity under submerged fermentation by Pleurotus ostreatus and Pleurotus cirinopileatus Sing. Laccase is a kind of widly used enzyme, it is worthy to find solution to solve the problem of lack of feedstuff in feed production.By several individual factor optimizing trials and multi-factor optimizing trails, we detected the desired laccase with higher activity. Under proper culture condition , Pleurotus ostreatus could produce laccase, whose activity was 358μmol·min-1·L-1;as well, the laccase activity was 830μmol·min-1·L-1 produced by Pleurotus cirinopileatus Sing.4,After optimizing trails on enhancing laccase activity, tests on optimizing maize stover fermentation processing were performed on. Lignin component decreased obviously. During a series of experiments, the highest lignin degradation rate was 62% by Pleurotus ostreatus; 67% by Pleurotus cirinopileatus Sing; 54% by B7; 70% by F8.5,Research on solid state fermentation showed high laccase activity produced by Pleurotus cirinopileatus Sing, reached to around 2350μmol·min-1·L-1, towered above the laccase activity by submerged fermentation nearly three times. Laccase activity was 780μmol·min-1·L-1 twice by Pleurotus ostreatus than that produced by submerged fermentation. However, the laccase activity was relatively low, about 40 to 50μmol·min-1·L-1,produced by B7, and the laccase activity was 240μmol·min-1·L-1, produced by F8.6,Solid state fermentation was divided into three parts. In each part, experiment carried on studying the effect of interaction among strains on laccase activity. In the first part, it investigated the effect of individual action and interaction of B7, Pleurotus ostreatus and Pleurotus cirinopileatus Sing on laccase. Based on this concept, the best strategy on strain combination was the combination of two white-rot fungus that was good to producing laccase with high activity. In the second part, it investigated the effect of individual action and interaction of F8, Pleurotus ostreatus and Pleurotus cirinopileatus Sing on laccase. Based on this concept, the best strategy was to let Pleurotus cirinopileatus Sing ferment only that was good to producing laccase with high activity. In the last stage, it investigated the effect of individual action and interaction of B7,F8, Pleurotus ostreatus and Pleurotus cirinopileatus Sing on laccase. Based on this concept, the best strategy was to use the whole four strains, under this condition it was good for producing laccase with high activity.7,The results of solid state fermentation showed that after fermentation by B7 , lignin content was 5.4%, its degradation rate was 61%; and for F8 lignin content was 5.4%, lignin degradation rate was 62%; the same state was that lignin content was 7%, lignin degradation rate was49% fermented by Pleurotus ostreatus; lignin content was 7.2%, lignin degradation rate was 48% fermented by Pleurotus cirinopileatus Sing.8,After fermentation, we carried on sensory evaluation on maize stover, these trial strains were all good at lignin degradation, and after bio-fermentation, the maize stover was a kind of fine roughage feed.