| In the industrial fermentation production of polyunsaturated fatty acids(PUFAs), The strains of Mortierella are the only sorts of fungi having authority with edible lipid safety assessment. With the increasing need of production of modern fermentation industry, the volume and the scale of fermentation tank becoming larger and larger, which put forward higher requirements to the number and vitality of fermented seeds, especially for the large scale of fermentation of Mortierella alpina. Due to the limitation of the number of seeds with exuberant metabolism, progressively expanding culture usually has to be adopted. If the low inoculum density doesn't lead to low growth rate and production, the fermention period and the cost of industrial production can be reduced significantly, which is the final purpose of this thesis. By integration of quorum-sensing system of microorganism, the influence of inoculum density to the growth rate has been revealed. The quorum-sensing system of Mortierella alpina has been tested and verified preliminarily in this thesis, which can be applied to the industrial production of Mortierella alpine. Research achievements are as follows:(1)The presence of quorum-sensing molecules of Mortierella alpina has been confirmed:A stable manner of inoculation and a gradient density fermentation modle(the volume rations are 10%,8%,6%,4% and 2%)has been established. By means of detecting dry biomass?lipids yield?residual glucose concentration and pH, the critical inoculum density of Mortierella alpina in fermentation, the volume ration of which is between 2% and 4%, has been determined. Through the conditioned culture and culture in connected bottles, the quorum-sensing system of Mortierella alpina, in which quorum-sensing molecules play an important role, has been preliminarily verified. The quorum-sensing molecules are self-induced and free-flowing in the medium. Within a certain range, higher cell density leading to a greater concentration of quorum-sensing molecules. It's only when the concentration of quorum sensing molecules reaches a certain threshold, the quorum-sensing phenomenon is relatively significant. The beginning inoculum density is related to the significance of quorum-sensing. Theoretically, when the beginning inoculum density is lower than the critical inoculum density, the quorum-sensing phenomenon is not significant, with a lower growth rate, a longer lag phase, a smaller biomass and production. And quorum-sensing dose exist in the regular inoculum density of 10%.(2)The elemental chemical properties of quorum-sensing molecules have been preliminarily determined:A series of analytical chemistry methods has been adopted, such as high temperature treatment, vacuum distillation, liquid to liquid extraction, etc. The final results revealed that quorum-sensing molecules were non-proteins organic molecule with moderate molecular polarity and high boiling point. And the quorum-sensing molecules are easily extracted by butyl alcohol from condensed fermented medium, which has laid the foundation of separation, purification and identification of quorum-sensing molecules.(3)Several exogenous quorum-sensing molecules have relatively siginificant influence on the growth regulation of Mortierella alpine: It is reported that farnesol, geraniol and phenylethyl alcohol are three kinds of quorum-sensing molecules. When they are added to the fermented medium in the concentration of 100?mol/L, only phenylethyl alcohol has significant influence to the growth rate and metabolic activity of Mortierella alpina. And through the component analysis of the final lipids, this three kind of molecules don't affect the anabolic pathways of PUFAs.What have been done above can somehow provide important theoretical and practical value for the establishment of high-productivity industrial production technology with low inoculum density of Mortierella alpina. |
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