Study On Process Engineering Of Taxus Media Cells Suspension Cultures Grown In A Bioreacto

Taxol, a diterpenoid secondary metabolite of the Taxus species, is an effective anticancer drug. Cell suspension cultures of Taxus media in a bioreactor is an effective method for taxol production. Although significant progress on Taxus cell culture for production of Paclitaxel has been made recently, and commercial applications of cell culture for paclitaxel production is still limited by the productivity of paclitaxel, kinetic simulation and scale-up for cell culture in a reactor.The objective of this work was to study fluid flow, mass transfer, cell growth and biochemical reaction in a bioreactor, to establish the mathematical models suitable for suspension cultures of Taxus media cells,and to provide a theoretical basis for the reactor design, amplification and operation optimization by combining the cell culture and process engineering theory. The main research conclusions in this paper are as follows:(1) This work constituted a set of unstructured kinetic models suitable for suspension cultures of Taxus media cells in bioreactors under substrate-sufficient conditions, including a logistic model for cell growth and models incorporating energy spilling for substrate consumption and product synthesis.Results of cross-validation and external validation demonstrated that a set of unstructured kinetic models constituted.in this paper should be suitable for suspension cultures of Taxus media cells in a15-L bioreactor under substrate-sufficient conditions, and helpful in the process prediction and operation optimization to guide the production and amplification of Taxus media cell suspension cultures in bioreactors. Energy spilling was a key factor that must be considered in a stirred bioreactor under substrate-sufficient conditions. The influence of energy spilling on cell growth and biochemical reactions in a stirred bioreactor under substrate-sufficient conditions was so significant that limiting substrate excess conditions should be maintained for scaled-up cultures of Taxus cells in a bioreactor to reduce energy spilling.(2) The determination method of apparent viscosity of Taxus media cell suspension culture broth was proposed. Results showed that the initial cultures broth of Taxus media suspension cells were rheologically Newtonian ones when cell inoculum size was equal or less than8%and the initial broth rheology exhibited non-Newtonian behavior when cell inoculum size was more than8%. Results also demonstrated that the suspension cultures broth of Taxus media cells at different culture time exhibited pseudoplastic non-Newtonian fluid, and the cell concentration was the main factor of apparent viscosity of culture broth. This work established quantitative relation between the apparent viscosity and influencing factors.(3) This work constituted a unstructured kinetic models of rheological behavior, proposed that energy spilling was an important factor which influenced the rheological behavior.(4) The determination method of the oxygen transfer coefficient of cell suspension culture broth was proposed, and the influence of cell biomass, apparent viscosity, agitator type, stirring speed and ventilation on oxygen transfer coefficient of cell suspension culture broth were studied.(5) The changes of the energy spilling-associated coefficients, the rates of the energy spilling-associated coefficient with culture time were studied, Results showed that carbon and energy consumed by energy spilling were larger during the early stage of the exponential growth phase, the energy spilling-associated rate of taxol synthesis played a key regulatory role between cell biomass and product concentration. To make larger the rate of product synthesis and improve product concentration, it was necessary to try to reduce or increase the cell concentration in the culture broth, for example, two phase culture, culture separation coupling, two stage culture, fed-batch culture.(6) An optimized operation strategy of limiting added carbon several times culture was proposed. A17.64%increase in cell growth was obtained, and a14.88%increase in taxol production was also obtained, while limiting added carbon several times was experimentally implemented in the15-L bioreactor.