Biodesign Swette Center for Environmental Biotechnology, Arizona State University, Tempe, Arizona, USA.
Skyology Inc., San Francisco, California, USA.
Biotechnol Bioeng. 2023 Jul;120(7):1844-1856. doi: 10.1002/bit.28415. Epub 2023 May 6.
Hydrogen (H ) concentrations that were associated with microbiological respiratory processes (RPs) such as sulfate reduction and methanogenesis were quantified in continuous-flow systems (CFSs) (e.g., bioreactors, sediments). Gibbs free energy yield (ΔǴ ~ 0) of the relevant RP has been proposed to control the observed H concentrations, but most of the reported values do not align with the proposed energetic trends. Alternatively, we postulate that system characteristics of each experimental design influence all system components including H concentrations. To analyze this proposal, a Monod-based mathematical model was developed and used to design a gas-liquid bioreactor for hydrogenotrophic methanogenesis with Methanobacterium bryantii M.o.H. Gas-to-liquid H mass transfer, microbiological H consumption, biomass growth, methane formation, and Gibbs free energy yields were evaluated systematically. Combining model predictions and experimental results revealed that an initially large biomass concentration created transients during which biomass consumed [H ] rapidly to the thermodynamic H -threshold (≤1 nM) that triggerred the microorganisms to stop H oxidation. With no H oxidation, continuous gas-to-liquid H transfer increased [H ] to a level that signaled the methanogens to resume H oxidation. Thus, an oscillatory H -concentration profile developed between the thermodynamic H -threshold (≤1 nM) and a low [H ] (~10 nM) that relied on the rate of gas-to-liquid H -transfer. The transient [H ] values were too low to support biomass synthesis that could balance biomass losses through endogenous oxidation and advection; thus, biomass declined continuously and disappeared. A stable [H ] (1807 nM) emerged as a result of abiotic H -balance between gas-to-liquid H transfer and H removal via advection of liquid-phase.
在连续流动系统（CFS）（例如生物反应器、沉积物）中定量了与微生物呼吸过程（RP）如硫酸盐还原和产甲烷相关的氢（H）浓度。相关 RP 的吉布斯自由能产率（ΔG0）被提议控制观察到的 H 浓度，但大多数报道的值与提出的能量趋势不一致。相反，我们假设每个实验设计的系统特性会影响包括 H 浓度在内的所有系统组件。为了分析这一假设，我们开发了一个基于 Monod 的数学模型，并将其用于设计一个带有 Methanobacterium bryantii M.o.H 的氢气产甲烷生物反应器。氢气-液体的气-液 H 传质、微生物 H 消耗、生物量增长、甲烷形成和吉布斯自由能产率被系统地评估。模型预测和实验结果的结合表明，最初较大的生物量浓度在瞬态期间迅速消耗[H]至触发微生物停止 H 氧化的热力学 H 阈值（≤1 nM）。由于没有 H 氧化，连续的气-液 H 传递增加了[H]，达到了提示产甲烷菌恢复 H 氧化的水平。因此，在热力学 H 阈值（≤1 nM）和低[H]（~10 nM）之间形成了一个 H 浓度的振荡轮廓，这依赖于气-液 H 传递的速率。瞬态[H]值太低，不足以支持通过内源性氧化和对流来平衡生物量损失的生物量合成；因此，生物量持续下降并消失。由于气-液 H 传递和通过液相对流去除 H 之间的非生物 H 平衡，稳定的[H]（1807 nM）出现了。
