Economic and bioenergetic controls on microbial metabolism of complex substrates in soils (EcoEnergeticS)

土壤中物质和能量的基本通道是微生物的代谢反应，符合负吉布斯自由能变化等热力学原理。因此，除了需要胞外酶来获取底物外，还需要分解代谢能能反应来为生物质合成的高能量反应提供燃料。因此，生物能和细胞经济原理将成为EcoEnergeticS开发的热力学代谢方法的基础。我们旨在通过表征微生物效率的五个指标：1)基质利用效率，2)碳利用效率，3)生化效率，4)热肺比和5)热力学效率来了解土壤中简单和复杂基质的微生物利用。我们期望在需要很少代谢转化的不同单体前体的生物量生长效率与从不同聚合物中释放这些单体的复杂酶系统的低效率之间进行权衡。因此，我们假设微生物效率在中等基质复杂性下是最佳的，这是由微生物群落的合作功能多样性及其土壤栖息地的边界条件调节的。通过扩展，我们假设微生物坏死团的复杂性解释了它在土壤系统中的埋藏。在WP1中，我们在土壤代谢通量分析（MFA）中实施了热力学约束，以分析和模拟微生物在化学上不同的基质上以不同的水平进入中心碳代谢。考虑到满足细胞复制生物合成途径需求的前体比例的优势，单体多样性对微生物生长和利用效率的影响将在WP2中量化。WP3研究了在能量不利的生长条件下，衬底的另一种用途-储存化合物形成-作为能量储存策略。在WP4中，我们使用MFA和酶经济方法阐明了由于聚合物在土壤中作为C源的优势而产生的外泌酶生产的额外成本。功能多样的微生物群落之间通过“外酶共享”的协同能量增益将成为WP5的目标。WP6将微生物栖息地的时空边界条件作为外酶经济学的关键因素，将底物利用的生物能维度与不同土壤复杂性水平的联合CERES实验相结合，作为物质和能量利用渠道的预测因子。综上所述，将建立一个基于系统生态学的生物能量概念，研究土壤中基质的利用和通道，将物质和能量通量分解到生化途径的水平。考虑到土壤生境边界条件的复杂因素，微生物代谢的热力学约束将与资源经济联系起来。因此，该项目将为土壤系统提供生物能量学和资源经济学的统一概念。

The fundamental channels of matter and energy in soils are the reactions of microbial metabolism, which conform to thermodynamic principles such as negative Gibbs free energy change. Consequently, catabolic exergonic reactions are needed to fuel the energy-demanding reactions of biomass synthesis in addition to extracellular enzymes to access substrates. Therefore, bioenergetic and cell economic principles will underlie the thermodynamic-metabolic approach developed by EcoEnergeticS. We aim at understanding microbial use of simple and complex substrates in soils by characterizing five proxies of microbial efficiency: 1) substrate use efficiency, 2) carbon use efficiency, 3) biochemical efficiency, 4) calorespirometric ratio, and 5) thermodynamic efficiency. We expect a trade-off between the efficiency of biomass growth on diverse monomeric precursors that require little metabolic conversion, and the inefficiencies of producing complex enzyme systems to liberate these monomers from diverse polymers. We therefore hypothesize an optimum of microbial efficiency at intermediate substrate complexity, modulated by the cooperative functional diversity of microbial communities and their soil habitats’ boundary conditions. By extension, we hypothesize that the complexity of microbial necromass accounts for its entombing in SoilSystems.In WP1, we implement thermodynamic constraints in soil metabolic flux analysis (MFA) to analyze and model microbial growth on chemically diverse substrates entering central C metabolism at different levels. The impact of monomer diversity on microbial growth and use efficiencies will be quantified in WP2, considering the advantages of precursor ratios that meet the demand of biosynthetic pathways for cell replication. WP3 investigates an alternative substrate use – storage compound formation – as an energy storing strategy under energetically unfavorable growth conditions. In WP4 we shed light on the additional costs of exoenzyme production arising from the predominance of polymers as C sources in soils, using MFA and enzyme economic approaches. Cooperative energy gains by “exoenzyme sharing” among functionally diverse microbial communities will be targeted in WP5. WP6 implements spatio-temporal boundary conditions of microbial habitats as crucial factors of exoenzyme economics, coupling the bioenergetic dimension of substrate use to the joint CERES experiment on various levels of soil complexity as predictors of matter and energy-use channels. Summarizing, a systems-ecology-based bioenergetic concept on substrate use and channeling in soils will be developed, resolving matter and energy fluxes down to the level of biochemical pathways. Thermodynamic constraints of microbial metabolism will be linked with resource economy, considering complex factors of habitat boundary conditions in soils. Thus, this project will provide a unifying concept of bioenergetics and resource economics to SoilSystems.