Duboc P, Marison I, von Stockar U
Institute of Chemical Engineering, Swiss Federal Institute of Technology, Lausanne, Switzerland.
J Biotechnol. 1996 Oct 18;51(1):57-72. doi: 10.1016/0168-1656(96)01566-0.
Synchronized populations of Saccharomyces cerevisiae CBS 426 are characterized by autonomous oscillations of process variables. CO2 evolution rate, O2 uptake rate and heat production rate varied by a factor of 2 for a continuous culture grown at a dilution rate of 0.10 h-1. Elemental analysis showed that the carbon mass fraction of biomass did not change. Since the reactor is not at steady state, the elemental and energy balances were calculated on cumulated quantities, i.e. the integral of the reaction rates. It was possible to show that carbon, degree of reduction and energy balances matched. Application of simple mass balance principles for non-steady state systems indicated that oscillations were basically characterized by changes in biomass production rate. In addition, the amount of intermediates, e.g. ethanol or acetate, produced or consumed was negligible. Growth rate was low during the S-phase (0.075 h-1) and high during the G2, M and G1 phases (0.125 h-1) for a constant dilution rate of 0.10 h-1. However, nitrogen, ash, sulfur and potassium content showed systematic increases during the S-phase (bud initiation). Cell component analyses showed that changes in cellular fractions during oscillations (storage carbohydrate content decreased during the S-phase) were due to changes in production rates, particularly for protein and carbohydrates. Nevertheless, using the data evaluation techniques for dynamic systems presented here, it was shown that storage carbohydrates are not consumed during the S-phase. Only the synthesis rate of the different cell components changed depending on position in cell cycle. The growth process may be divided into two phenomena: the formation of new cells during mitosis with a low yield, and size increase of new born cells with high yield. Both kinetic and stoichiometric coefficients varied with the position in the oscillation: the results showed that biomass structure changed and that specific growth rate, as well as biomass yield, varied by +/- 25% during the oscillation.
酿酒酵母CBS 426的同步群体以过程变量的自主振荡为特征。对于以0.10 h⁻¹的稀释率进行连续培养的情况，二氧化碳释放速率、氧气摄取速率和产热速率变化了2倍。元素分析表明，生物质的碳质量分数没有变化。由于反应器未处于稳态，因此基于累积量（即反应速率的积分）计算元素和能量平衡。结果表明，碳、还原度和能量平衡相匹配。对非稳态系统应用简单的质量平衡原理表明，振荡的基本特征是生物质生产率的变化。此外，产生或消耗的中间体（如乙醇或乙酸盐）的量可以忽略不计。对于0.10 h⁻¹的恒定稀释率，在S期生长速率较低（0.075 h⁻¹），而在G2、M和G1期较高（0.125 h⁻¹）。然而，氮、灰分、硫和钾含量在S期（芽开始形成）呈现系统性增加。细胞成分分析表明，振荡期间细胞组分的变化（储存碳水化合物含量在S期降低）是由于生产率的变化，特别是蛋白质和碳水化合物的生产率变化。尽管如此，使用本文介绍的动态系统数据评估技术表明，储存碳水化合物在S期并未被消耗。只是不同细胞组分的合成速率根据细胞周期中的位置而变化。生长过程可分为两种现象：有丝分裂期间新细胞形成，产率较低；新生细胞体积增大，产率较高。动力学和化学计量系数均随振荡位置而变化：结果表明，生物质结构发生了变化，在振荡期间比生长速率以及生物质产率变化了±25%。
