On the feasibility of growth-coupled product synthesis in microbial strains
On the feasibility of growth-coupled product synthesis in microbial strains
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DOI：
10.1016/j.ymben.2015.05.006
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发表时间：
2015-07-01
影响因子：
8.4
通讯作者：
Mahadevan, Radhakrishnan
中科院分区：
文献类型：
--
作者：
Klamt, Steffen;Mahadevan, Radhakrishnan
强制生长与所需产物合成的强制性耦合已成为微生物生产菌株代谢工程的关键原则。从化学计量学和基于约束的建模的各种方法已经被开发出来计算干预策略，通过这些策略，给定的微生物只能在合成所需化合物作为强制性副产品时才能生长。然而，生长偶联合成并不一定适用于代谢网络中的每一种化合物，目前还没有严格的标准来测试偶联产物和生物量形成的可行性（在寻找合适的干预策略之前）。在这项工作中，我们展示了网络必须满足哪些性质，以便保证耦合生物量和产品合成的应变设计可以存在。在没有通量边界的网络中，耦合是可行的，当且仅当存在导致生物量和产品同时形成的基本模式。利用初等（通量）矢量的概念，即初等模态的推广，也可以推导出这种情况下的可行性判据。我们将我们的标准应用于大肠杆菌的代谢模型，并确定了每种代谢物的净产量是否可以与生物量合成耦合，并计算了最大（保证）耦合产量。有些令人惊讶的结果是，在有氧条件下，中枢代谢的每种碳代谢物确实可以偶联。这也适用于厌氧条件下的大多数代谢物，但考虑到ATP维持需求意味着某些化合物不可能偶联。另一方面，ATP的维持也可能增加某些代谢物的最大偶联产率。总的来说，我们的工作为计算应变设计的核心问题提供了重要的见解和新颖的工具。(C) 2015年国际代谢工程学会。Elsevier Inc.出版。版权所有。
Enforcing obligate coupling of growth with synthesis of a desired product has become a key principle for metabolic engineering of microbial production strains. Various methods from stoichiometric and constraint-based modeling have been developed to calculate intervention strategies by which a given microorganism can only grow if it synthesizes a desired compound as a mandatory by-product. However, growth-coupled synthesis is not necessarily feasible for every compound of a metabolic network and no rigorous criterion is currently known to test feasibility of coupled product and biomass formation (before searching for suitable intervention strategies). In this work, we show which properties a network must fulfill such that strain designs guaranteeing coupled biomass and product synthesis can exist at all In networks without flux bounds, coupling is feasible if and only if an elementary mode exists that leads to formation of both biomass and product Setting flux boundaries leads to more complicated inhomogeneous problems. Making use of the concept of elementary (flux) vectors, a generalization of elementary modes, a criterion for feasibility can also be derived for this situation. We applied our criteria to a metabolic model of Escherichia coli and determined for each metabolite, whether its net production can be coupled with biomass synthesis and calculated the maximal (guaranteed) coupling yield. The somewhat surprising result is that, under aerobic conditions, coupling is indeed possible for each carbon metabolite of the central metabolism. This also holds true for most metabolites under anaerobic conditions but consideration of ATP maintenance requirements implies infeasibility of coupling for certain compounds. On the other hand, ATP maintenance may also increase the maximal coupling yield for some metabolites. Overall, our work provides important insights and novel tools for a central problem of computational strain design. (C) 2015 International Metabolic Engineering Society. Published by Elsevier Inc. All rights reserved.