Max Planck Institute for Terrestrial Microbiology, Karl-von-Frisch-Str. 10, 35043 Marburg, Germany.
Max Planck Institute for Terrestrial Microbiology, Karl-von-Frisch-Str. 10, 35043 Marburg, Germany.
Curr Opin Biotechnol. 2016 Oct;41:122-129. doi: 10.1016/j.copbio.2016.07.001. Epub 2016 Aug 31.
While the structure of microbial communities can nowadays be determined by applying molecular analytical tools to soil samples, microbial function can usually only be determined by physiological experiments requiring incubation of samples. However, analysis of stable isotope fractionation might be able to analyse microbial function without incubation in soil samples. We describe the limitations of diagnosing and quantifying carbon flux pathways in soil by using the determination of stable carbon isotope composition in soil compounds and emphasize the importance of determining stable isotope fractionation factors for defined biochemical pathways. Fractionation factors are sufficiently different for some central biochemical pathways in anaerobic degradation of organic carbon. Thus, it is possible to quantify the relative contribution of CH production by hydrogenotrophic or aceticlastic methanogenic pathways, and of acetate formation by chemolithotrophic (acetyl-CoA synthase) or heterotrophic (fermentation) pathways. In addition, stable isotope analysis may allow the differentiation between different organic substrates used for degradation, for example, the relative contribution of root exudation versus soil organic matter degradation, provided the different substrates are sufficiently distinct in their isotopic compositions (e.g., mixture of C and C plants) and the carbon conversion pathways display only small fractionation factors or are identical for the different substrates.
虽然现在可以通过向土壤样本中应用分子分析工具来确定微生物群落的结构，但微生物的功能通常只能通过需要培养样本的生理实验来确定。然而，稳定同位素分馏分析可能能够在不培养土壤样本的情况下分析微生物的功能。我们描述了通过测定土壤化合物中的稳定碳同位素组成来诊断和量化土壤中碳通量途径的局限性，并强调了确定定义明确的生化途径的稳定同位素分馏因子的重要性。对于有机碳的厌氧降解中的一些核心生化途径，分馏因子存在足够大的差异。因此，可以定量确定由氢营养型或乙酸营养型产甲烷途径产生的 CH4 的相对贡献，以及由化能自养（乙酰辅酶 A 合酶）或异养（发酵）途径产生的乙酸的形成。此外，稳定同位素分析可以允许区分用于降解的不同有机底物，例如，根分泌物与土壤有机质降解的相对贡献，前提是不同的底物在其同位素组成上有足够大的差异（例如，C 和 C 植物的混合物），并且碳转化途径仅显示较小的分馏因子或对于不同的底物是相同的。
