The Growth And Metabolism Properties Of Microbial Cells Immobilized By Polymeric Carrier In Nonaqueous Media

Biocatalysis has the advantages of high selectivity, mild reaction conditions and to environment friendly, so it developed a rapidly in biotechnology field. But there still exsit several limitations such as low substrate solubility, biocatalyst activity inhibition and product degradation. The introduction of nonaqueous media especially water-organic solvent system could solve these problems very well. The activity of many cells may decrease and even lose in organic solvents. The application of immobilization technology not only benefits to the cells separation or reuse, but also prevents the cells from direct contact with organic solvents, which results in the improvement of cell activity and stability. Therefore, the establishment of nonaqueous biocatalysis system with immobilized cells is important to the production of oil-soluble substances.Taking Saccharomyces cerevisiae as the cell model, the alginate-chitosan(AC) microcapsules were prepared as immobilization carrier for nonaqueous biocatalysis. With the characterization methods including laser particle size analyzer, UV spectrophotometer, high performance liquid chromatography (HPLC) and biological inverted microscope, the biotransformation ability of AC microencapsulated yeast cells were studied to improve the metabolite production. The results have laid a good foundation for the industrial application of nonaqueos biocatalysis system with immobilized cells.The specific contents and conclusions of the study are as follows:(1) Calcium alginate beads were prepared by emulsification-internal gelation process and used for the preparation of AC microcapsules. The growth and metabolism property of free cells, alginate bead immobilized cells and AC microencapsulated cells were studied in aqueous phase. The results indicated that the metabolic product concentration has not much difference in three cultivation modes but the cell concentrations have obvious difference. Considering the severe leakage of alginate bead immobilized cells AC microcapsules were chosen as the immobilization carrier for subsequent experiments.(2) In order to reduce product inhibition effect and cell toxicity and improve the production, water-oil two-phase culture system was used for cell transformation experiments. The influence of preparation and culture conditions of AC microencapsulated cells were studied on the cell growth and metabolism properties. The results showed that chitosan molecular weight, alginate beads size and oil-water rate had significant influence on cell growth and metabolism properties. The total2-PEA concentration of5.15g/L was achieved at optimized conditions.(3) On this basis, batch fermentation experiments were studied with free culture as control. Along with the increase of culture batches, cell concentration increased gradually, metabolic product concentration increased firstly and decreased, and reached maximum value5.84g/L in the second batch; While cell concentration in microcapsules showed not obvious trend of first increase and then decrease, product concentration dropped and no significant difference among each batch. The results demonstrated that the biotransformation of production process with AC microencapsulated microbial cells has good stability.