Direct incorporation of fatty acids into microbial phospholipids in soils: Position-specific labeling tells the story
Direct incorporation of fatty acids into microbial phospholipids in soils: Position-specific labeling tells the story
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DOI：
10.1016/j.gca.2015.10.032
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发表时间：
2016-02
影响因子：
5
通讯作者：
M. Dippold;Y. Kuzyakov
中科院分区：
文献类型：
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作者：
M. Dippold;Y. Kuzyakov
脂肪酸已被用作植物和微生物的生物标志物，了解其在土壤和沉积物中的转化途径对于解释脂肪酸特征至关重要，特别是因为脂肪酸的形成、循环和分解过程是同时进行的。通过结合位置特异性的13C标记和化合物特异性的13C分析，我们分析了游离脂肪酸在土壤微生物脂肪酸中的掺入情况。通过分析微生物对棕榈酸酯各个分子位置的13C的利用及其与磷脂脂肪酸(PLFA)的结合来追踪脂肪酸的途径。棕榈酸酯13C在土壤中的去向由微生物脂肪酸代谢的主要途径决定：在柠檬酸循环中，奇数位(C-1)优先氧化为CO2，而偶数位(C-2)优先结合到微生物生物量中。这种模式是棕榈酸裂解为乙酰辅酶A的结果，并进一步用于C代谢的主要途径。我们观察到添加的棕榈酸酯的4%以上直接、完整地掺入到微生物细胞膜的PLFA中，表明棕榈酸酯作为微生物脂肪酸的直接前体具有重要作用。棕榈酸酯13C以完整的烷基链形式掺入PLFA中，即棕榈酸酯的C主链不被切割，但棕榈酸酯可以完整地或修饰(如脱饱和、延长或支化)结合到PLFA中，根据微生物群落的脂肪酸需求。所结合的棕榈酸酯的这些修饰随时间增加。因此，未来的PLFA研究必须考虑现有植物和微生物衍生的脂肪酸的循环利用。这项研究证明了土壤中棕榈酸酯等游离脂肪酸的完整吸收和循环，以及细胞PLFA的高周转和转化。关于土壤来源的游离脂肪酸的完整吸收和使用的知识对于解释微生物脂肪酸指纹及其同位素组成至关重要。
Fatty acids have been used as plant and microbial biomarkers, and knowledge about their transformation pathways in soils and sediments is crucial for interpreting fatty acid signatures, especially because the formation, recycling and decomposition processes are concurrent. We analyzed the incorporation of free fatty acids into microbial fatty acids in soil by coupling position-specific13C labeling with compound-specific13C analysis.Position-specifically and uniformly13C labeled palmitate were applied in an agricultural Luvisol. Pathways of fatty acids were traced by analyzing microbial utilization of13C from individual molecule positions of palmitate and their incorporation into phospholipid fatty acids (PLFA).The fate of palmitate13C in the soil was characterized by the main pathways of microbial fatty acid metabolism: Odd positions (C-1) were preferentially oxidized to CO2in the citric acid cycle, whereas even positions (C-2) were preferentially incorporated into microbial biomass. This pattern is a result of palmitate cleavage to acetyl-CoA and its further use in the main pathways of C metabolism. We observed a direct, intact incorporation of more than 4% of the added palmitate into the PLFA of microbial cell membranes, indicating the important role of palmitate as direct precursor for microbial fatty acids. Palmitate13C was incorporated into PLFA as intact alkyl chain, i.e. the C backbone of palmitate was not cleaved, but palmitate was incorporated either intact or modified (e.g. desaturated, elongated or branched) according to the fatty acid demand of the microbial community. These modifications of the incorporated palmitate increased with time. Future PLFA studies must therefore consider the recycling of existing plant and microbial-derived fatty acids.This study demonstrates the intact uptake and recycling of free fatty acids such as palmitate in soils, as well as the high turnover and transformation of cellular PLFA. Knowledge about the intact uptake and use of soil-derived free fatty acids is crucial for interpreting microbial fatty acid fingerprints and their isotopic composition.