Abstract Branched glycerol dialkyl glycerol tetraethers (bGDGTs) are unique ether-linked bacterial membrane lipids, which occur in diverse environments. Acidobacteria are considered to produce them in acidic soils and peat bogs. However, the biological source(s) of bGDGTs other than acidobacteria in alkaline soils and their response to environmental changes are obscure. We designed a 1 year incubation experiment under elevated temperature conditions (30 °C, 45 °C and 85 °C) in order to accelerate the growth of mesophilic and thermophilic bacteria that may potentially produce bGDGTs and to understand the mechanisms underlying the changes in bGDGT composition. The soil we selected was alkaline (pH > 8) with a small population of acidobacteria being detected using high throughput sequencing. The medium contained nutrients and organic carbon and samples were incubated under anaerobic conditions with pH of 7.5, in order to stimulate the growth of heterotrophic and anaerobic bacteria from the soil. Quantitative polymerase chain reaction (qPCR) was employed to monitor the growth status of bacteria at the beginning and the end of the experiment. The results showed multiple lines of evidence for bGDGT biosynthesis, including: (1) increased total abundance of both PL-bGDGTs (polar lipid-derived bGDGTs, “living”) and CL-bGDGTs (core lipid bGDGTs, “dead”) at 30 °C and 45 °C, but not 85 °C; (2) changes in bGDGT distribution at 30 °C and 45 °C; and (3) increased temperature inferred by the bGDGT-based proxy at an incubation temperature at 45 °C. Estimated turnover time of both PL- and CL-bGDGTs was 1–8 months at 30 °C or 45 °C under these laboratory conditions, which agrees with previous studies. Our study suggests that raising temperature may stimulate growth of bGDGT-producing bacteria that likely includes some anaerobic heterotrophs other than acidobacteria.

中文翻译：

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在厌氧土壤微观孵化中在升高的温度下产生分支的 GDGT

摘要 支化甘油二烷基甘油四醚 (bGDGTs) 是独特的醚连接细菌膜脂，存在于多种环境中。酸细菌被认为在酸性土壤和泥炭沼泽中产生它们。然而，碱性土壤中除酸菌外的 bGDGT 的生物来源及其对环境变化的反应尚不清楚。我们设计了一个在高温条件下（30°C、45°C 和 85°C）进行为期 1 年的孵化实验，以加速可能产生 bGDGT 的嗜温和嗜热细菌的生长，并了解 bGDGT 变化的潜在机制作品。我们选择的土壤是碱性的（pH > 8），使用高通量测序检测到少量酸细菌。培养基含有养分和有机碳，样品在 pH 为 7.5 的厌氧条件下培养，以刺激土壤中异养和厌氧细菌的生长。在实验开始和结束时，采用定量聚合酶链反应 (qPCR) 来监测细菌的生长状态。结果显示了 bGDGT 生物合成的多条证据，包括：（1）PL-bGDGT（极性脂质衍生的 bGDGT，“活的”）和 CL-bGDGT（核心脂质 bGDGT，“死的”）的总丰度在 30 °C 和 45 °C，但不是 85 °C；(2) 30℃和45℃时bGDGT分布的变化；(3) 在 45 °C 的孵育温度下，基于 bGDGT 的代理推断出的温度升高。在这些实验室条件下，PL- 和 CL-bGDGT 的估计周转时间在 30°C 或 45°C 下为 1-8 个月，这与之前的研究一致。我们的研究表明，升高温度可能会刺激产生 bGDGT 的细菌的生长，这些细菌可能包括除酸杆菌以外的一些厌氧异养菌。