Feyhl-Buska Jayme, Wu Fabai, Smith Isaiah E, LaRowe Douglas E, Robador Alberto, Kruger Brittany, Osburn Magdalena R, Amend Jan P
Department of Earth Sciences, University of Southern California, Los Angeles, CA, United States.
Department of Biological Sciences, University of Southern California, Los Angeles, CA, United States.
Front Microbiol. 2024 Dec 23;15:1455594. doi: 10.3389/fmicb.2024.1455594. eCollection 2024.
Microbial activity in the deep continental subsurface is difficult to measure due to low cell densities, low energy fluxes, cryptic elemental cycles and enigmatic metabolisms. Nonetheless, direct access to rare sample sites and sensitive laboratory measurements can be used to better understand the variables that govern microbial life underground. In this study, we sampled fluids from six boreholes at depths ranging from 244 m to 1,478 m below ground at the Sanford Underground Research Facility (SURF), a former goldmine in South Dakota, United States. The heat produced by microorganisms in these samples was measured in a nanocalorimeter as a proxy for activity. Heat flow measurements on unamended groundwater samples from five of the six boreholes comprising the Deep Underground Microbial Observatory (DeMMO) fell below the limit of detection, suggesting very low metabolic rates. Fluid samples from the borehole that registered a heat signal (DeMMO 6) from 1,478 m deep, were amended with a series of electron donors, electron acceptors, and amino acids before being introduced into the calorimeter. The addition of formate resulted in more than a ~500 nW increase in heat flow relative to the signal for unamended fluids during the first 100 h of incubation while the next highest heat flow arose from nitrate and acetate co-addition, at ~125 nW. Notably, both amendment conditions led to a ~1.5 orders of magnitude increase in cell density without causing major changes to community composition, suggesting that these electron donors and acceptors may be exploited by these communities . The addition of ~0.4 mM casamino acids resulted in a total heat flow of 2.25 μW within 35 h and a more than three orders of magnitude increase in cell density. In these experiments, grew to dominate the amino acid amended borehole fluids. The strong microbial response to amino acid addition indicates a deep continental surface community that is limited by the availability of amino acids. A high potential for amino acid metabolism was proposed in genomic studies from this and similar sites but has not been shown in actively growing communities.
由于细胞密度低、能量通量低、隐秘的元素循环和神秘的新陈代谢，很难测量大陆深部地下的微生物活动。尽管如此，直接进入稀有的采样点并进行灵敏的实验室测量，可以用来更好地理解控制地下微生物生命的各种变量。在本研究中，我们在美国南达科他州一个曾经的金矿——桑福德地下研究设施（SURF），从地下244米至1478米深处的六个钻孔中采集了流体样本。在纳米量热计中测量这些样本中微生物产生的热量，以此作为活动的指标。组成深部地下微生物观测站（DeMMO）的六个钻孔中的五个，其未添加物质的地下水样本的热流测量值低于检测限，这表明代谢率非常低。来自1478米深处记录到热信号的钻孔（DeMMO 6）的流体样本，在引入量热计之前，用一系列电子供体、电子受体和氨基酸进行了处理。添加甲酸盐后，在培养的前100小时内，相对于未添加物质的流体信号，热流增加了超过约500纳瓦，而第二高的热流来自硝酸盐和乙酸盐的共同添加，约为125纳瓦。值得注意的是，两种添加条件都使细胞密度增加了约1.5个数量级，而没有导致群落组成发生重大变化，这表明这些电子供体和受体可能被这些群落所利用。添加约0.4毫摩尔酪蛋白氨基酸在35小时内产生了2.25微瓦的总热流，细胞密度增加了三个多数量级。在这些实验中， 生长并在氨基酸处理过的钻孔流体中占主导地位。微生物对氨基酸添加的强烈反应表明，大陆深部地下群落受到氨基酸可用性的限制。在来自该地点及类似地点的基因组研究中提出了氨基酸代谢的高潜力，但尚未在活跃生长的群落中得到证实。
