Organic Geochemistry Unit, Bristol Biogeochemistry Research Centre, School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, UK.
Rapid Commun Mass Spectrom. 2012 Apr 30;26(8):997-1004. doi: 10.1002/rcm.6172.
Recent advances in stable isotope probing (SIP) have allowed direct linkage of microbial population structure and function. This paper details a new development of SIP, Stable Isotope Switching (SIS), which allows the simultaneous assessment of carbon (C) uptake, turnover and decay, and the elucidation of soil food webs within complex soils or sedimentary matrices.
SIS utilises a stable isotope labelling approach whereby the (13)C-labelled substrate is switched part way through the incubation to a natural abundance substrate. A (13)CH(4) SIS study of landfill cover soils from Odcombe (Somerset, UK) was conducted. Carbon assimilation and dissimilation processes were monitored through bulk elemental analysis isotope ratio mass spectrometry and compound-specific gas chromatography/combustion/isotope ratio mass spectrometry, targeting a wide range of biomolecular components including: lipids, proteins and carbohydrates.
Carbon assimilation by primary consumers (methanotrophs) and sequential assimilation into secondary (Gram-negative and -positive bacteria) and tertiary consumers (Eukaryotes) was observed. Up to 45% of the bacterial membrane lipid C was determined to be directly derived from CH(4) and at the conclusion of the experiment ca. 50% of the bulk soil C derived directly from CH(4) was retained within the soil.
This is the first estimate of soil organic carbon derived from CH(4) and it is comparable with levels observed in lakes that have high levels of benthic methanogenesis. SIS opens the way for a new generation of SIP studies aimed at elucidating total C dynamics (incorporation, turnover and decay) at the molecular level in a wide range of complex environmental and biological matrices.
最近在稳定同位素探测（SIP）方面的进展使得微生物种群结构和功能能够直接联系起来。本文详细介绍了 SIP 的一项新进展，即稳定同位素切换（SIS），它允许同时评估碳（C）的摄取、周转和衰减，并阐明复杂土壤或沉积基质中的土壤食物网。
SIS 利用稳定同位素标记方法，其中（13）C 标记的底物在孵育过程中被切换到自然丰度的底物。对英国萨默塞特奥多姆（Odcombe）垃圾填埋场覆盖土壤进行了（13）CH4 SIS 研究。通过总元素分析同位素比质谱和化合物特异性气相色谱/燃烧/同位素比质谱监测碳同化和异化过程，针对包括：脂质、蛋白质和碳水化合物在内的广泛生物分子成分。
观察到初级消费者（甲烷营养菌）的碳同化和随后的同化进入二级（革兰氏阴性和阳性细菌）和三级消费者（真核生物）。高达 45%的细菌膜脂 C 被确定直接来自 CH4，在实验结束时，约 50%的土壤 C 直接来自 CH4 保留在土壤中。
这是首次估计源自 CH4 的土壤有机碳，与具有高水平底栖甲烷生成的湖泊中的水平相当。SIS 为新一代 SIP 研究开辟了道路，旨在阐明复杂环境和生物基质中分子水平上的总 C 动态（同化、周转和衰减）。
