School of Life Sciences, University of Nevada, Las Vegas Las Vegas, NV, USA.
Front Microbiol. 2013 Aug 8;4:222. doi: 10.3389/fmicb.2013.00222. eCollection 2013.
Branched glycerol dialkyl glycerol tetraethers (bGDGTs) are membrane-spanning lipids that likely stabilize membranes of some bacteria. Although bGDGTs have been reported previously in certain geothermal environments, it has been suggested that they may derive from surrounding soils since bGDGTs are known to be produced by soil bacteria. To test the hypothesis that bGDGTs can be produced by thermophiles in geothermal environments, we examined the distribution and abundance of bGDGTs, along with extensive geochemical data, in 40 sediment and mat samples collected from geothermal systems in the U.S. Great Basin (temperature: 31-95°C; pH: 6.8-10.7). bGDGTs were found in 38 out of 40 samples at concentrations up to 824 ng/g sample dry mass and comprised up to 99.5% of total GDGTs (branched plus isoprenoidal). The wide distribution of bGDGTs in hot springs, strong correlation between core and polar lipid abundances, distinctness of bGDGT profiles compared to nearby soils, and higher concentration of bGDGTs in hot springs compared to nearby soils provided evidence of in situ production, particularly for the minimally methylated bGDGTs I, Ib, and Ic. Polar bGDGTs were found almost exclusively in samples ≤70°C and the absolute abundance of polar bGDGTs correlated negatively with properties of chemically reduced, high temperature spring sources (temperature, H2S/HS(-)) and positively with properties of oxygenated, low temperature sites (O2, NO(-) 3). Two-way cluster analysis and nonmetric multidimensional scaling based on relative abundance of polar bGDGTs supported these relationships and showed a negative relationship between the degree of methylation and temperature, suggesting a higher abundance for minimally methylated bGDGTs at high temperature. This study presents evidence of the widespread production of bGDGTs in mats and sediments of natural geothermal springs in the U.S. Great Basin, especially in oxygenated, low-temperature sites (≤70°C).
支链甘油二烷基甘油四醚（bGDGTs）是一种跨膜脂质，可能稳定某些细菌的膜。尽管以前在某些地热环境中报道过 bGDGTs，但有人认为它们可能来自周围的土壤，因为已知 bGDGTs是由土壤细菌产生的。为了检验 bGDGTs 可以由地热环境中的嗜热菌产生的假设，我们研究了美国大盆地（温度：31-95°C；pH：6.8-10.7）40 个地热系统的沉积物和垫状样品中 bGDGTs 的分布和丰度，以及广泛的地球化学数据。在 40 个样本中的 38 个样本中发现了 bGDGTs，浓度高达 824ng/g 样品干重，占总 GDGTs（支链加异戊二烯）的 99.5%。bGDGTs 在温泉中的广泛分布、核心和极性脂类丰度之间的强相关性、bGDGT 分布与附近土壤的明显区别，以及温泉中 bGDGTs 的浓度高于附近土壤，都提供了原位产生的证据，特别是对于最小甲基化的 bGDGTs I、Ib 和 Ic。极性 bGDGTs 几乎只存在于≤70°C 的样品中，极性 bGDGTs 的绝对丰度与化学还原、高温泉源的性质（温度、H2S/HS(-)）呈负相关，与含氧、低温地点的性质（O2、NO(-) 3）呈正相关。基于极性 bGDGTs 相对丰度的双向聚类分析和非度量多维尺度分析支持了这些关系，并显示出甲基化程度与温度之间的负相关关系，表明在高温下最小甲基化的 bGDGTs 丰度更高。本研究提供了美国大盆地自然地热泉垫状沉积物中 bGDGTs 广泛产生的证据，特别是在含氧、低温地点（≤70°C）。
