Sipkema E M, de Koning W, Ganzeveld K J, Janssen D B, Beenackers A A
Chemical Engineering and Biochemistry Departments, University of Groningen, NL-9747 AG Groningen, The Netherlands.
Biotechnol Prog. 2000 Mar-Apr;16(2):189-98. doi: 10.1021/bp990155e.
A metabolic model describing growth of Methylosinus trichosporium OB3b and cometabolic contaminant conversion is used to optimize trichloroethene (TCE) conversion in a bioreactor system. Different process configurations are compared: a growing culture and a nongrowing culture to which TCE is added at both constant and pulsed levels. The growth part of the model, presented in the preceding article, gives a detailed description of the NADH regeneration required for continued TCE conversion. It is based on the metabolic pathways, includes Michaelis-Menten type enzyme kinetics, and uses NADH as an integrating and controlling factor. Here the model is extended to include TCE transformation, incorporating the kinetics of contaminant conversion, the related NADH consumption, toxic effects, and competitive inhibition between TCE and methane. The model realistically describes the experimentally observed negative effects of the TCE conversion products, both on soluble methane monooxygenase through the explicit incorporation of the activity of this enzyme and on cell viability through the distinction between dividing and nondividing cells. In growth-based systems, the toxicity of the TCE conversion products causes rapid cell death, which leads to wash-out of suspended cultures at low TCE loads (below microM inlet concentrations). Enzyme activity, which is less sensitive, is hardly affected by the toxicity of the TCE conversion products and ensures high conversions (>95%) up to the point of wash-out. Pulsed addition of TCE (0.014-0.048 mM) leads to a complete loss of viability. However, the remaining enzyme activity can still almost completely convert the subsequently added large TCE pulses (0.33-0.64 mM). This emphasizes the inefficient use of enzyme activity in growth-based systems. A comparison of growth-based and similar non-growth-based systems reveals that the highest TCE conversions per amount of cells grown can be obtained in the latter. Using small amounts of methane (negligible compared to the amount needed to grow the cells), NADH limitation in the second step of this two-step system can be eliminated. This results in complete utilization of enzyme activity and thus in a very effective treatment system.
一个描述甲基弯曲菌OB3b生长和共代谢污染物转化的代谢模型被用于优化生物反应器系统中三氯乙烯（TCE）的转化。比较了不同的工艺配置：一种是生长培养物，另一种是不生长培养物，TCE以恒定和脉冲水平添加到不生长培养物中。上一篇文章中介绍的模型的生长部分，详细描述了持续TCE转化所需的NADH再生。它基于代谢途径，包括米氏酶动力学，并将NADH用作整合和控制因子。在此，该模型得到扩展以包括TCE转化，纳入了污染物转化动力学、相关的NADH消耗、毒性效应以及TCE与甲烷之间的竞争抑制。该模型真实地描述了实验观察到的TCE转化产物的负面影响，既通过明确纳入该酶的活性对可溶性甲烷单加氧酶产生影响，又通过区分分裂细胞和非分裂细胞对细胞活力产生影响。在基于生长的系统中，TCE转化产物的毒性导致细胞迅速死亡，这在低TCE负荷（低于微摩尔入口浓度）时导致悬浮培养物的洗出。酶活性对毒性不太敏感，几乎不受TCE转化产物毒性的影响，并确保在洗出点之前有高转化率（>95%）。TCE的脉冲添加（0.014 - 0.048 mM）导致活力完全丧失。然而，剩余的酶活性仍几乎能完全转化随后添加的大剂量TCE脉冲（0.33 - 0.64 mM）。这强调了基于生长的系统中酶活性利用效率低下。基于生长的系统与类似的非基于生长的系统的比较表明，后者每生长的细胞量可获得最高的TCE转化率。使用少量甲烷（与细胞生长所需量相比可忽略不计），可以消除这个两步系统第二步中的NADH限制。这导致酶活性的完全利用，从而形成一个非常有效的处理系统。
