Microorganisms in soil assimilate, transform, and mineralize soil C to support growth. There are an estimated 2.6 × 10²⁹ microbial cells containing 26 Pg C in soils worldwide. Consequently, quantifying microbial growth in soil is critical for determining the degree to which microorganisms contribute to the global C cycle. Measuring taxonspecific microbial growth enables understanding of the contribution of microbial taxa to elemental transformations across ecosystems and their susceptibility to environmental perturbations. These measurements in soil have largely been lacking due to inadequate methods. Quantitative stable isotope probing (qSIP) with H₂¹⁸O is used to measure taxon‐specific growth of microbial taxa in soil, an improvement compared with traditional stable isotope probing (SIP). In qSIP, DNA extracted from both a labeled (¹⁸O‐enriched water) and an unlabeled treatment is separated into numerous density fractions by isopycnic centrifugation, and target genes are quantified and sequenced in each fraction. The taxon‐specific DNA density shift and ultimately the isotopic composition (¹⁸O enrichment) is calculated for each taxon. Here we discuss methods and illustrate the procedure for quantifying microbial taxon‐specific growth in soil with qSIP using heavy isotope enriched H₂¹⁸O.

中文翻译：

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使用H218O进行定量稳定同位素探测以测量分类群特异性微生物的生长

土壤中的微生物会吸收，转化和矿化土壤C以支持生长。据估计，全球土壤中含有2.6 Pg C的2.6×10 ²⁹微生物细胞。因此，量化土壤中的微生物生长对于确定微生物对全球碳循环的贡献程度至关重要。通过测量特定分类群的微生物生长，可以了解微生物分类群对整个生态系统的元素转化的贡献及其对环境扰动的敏感性。由于方法不足，这些土壤中的测量值大都缺乏。H ₂ ^18的定量稳定同位素探测（qSIP）O用于测量土壤中微生物分类群的特定分类群生长，与传统的稳定同位素探测（SIP）相比，此改进。在qSIP中，通过等温离心将从标记的（富含¹⁸ O的水中）和未标记的处理中提取的DNA分为许多密度级分，并对每个级分中的靶基因进行定量和测序。计算每个分类单元的特定分类单元的DNA密度变化并最终计算出同位素组成（¹⁸ O富集）。在这里我们讨论方法并举例说明使用富含重同位素的H ₂ ¹⁸ O用qSIP量化土壤中微生物分类群特异性生长的过程。