Aerobic microbial activity in deep sea abyssal clay

据估计，海洋沉积物中含有100 ^ 10^29个微生物细胞，它们延伸到海底以下2500米。在这些非常稳定和古老的环境中，微生物细胞的分解代谢速度比营养丰富的培养物中的模式生物慢100万倍，据估计，它们的生长需要几千年的时间尺度，而不是几小时到几天。由于海底微生物的活动速率极低，因此研究海底微生物的具体活动具有挑战性。然而，海底微生物群落的转录活性现在可以通过亚转录组学来研究，即对从沉积物样品中提取的活性转录信息RNA （mRNA）进行高通量DNA测序。深海粘土表现出氧对基底的渗透，这是由于超贫营养海洋的低沉积速率所致。氧气的消耗是由缓慢呼吸的微生物群落驱动的，这些微生物群落的细胞数量和呼吸速率由于上覆的极贫营养海洋沉积的少量有机物而保持在极低的水平。这些需氧微生物群落长期生存的细胞机制尚不清楚。2014年，北大西洋探险队成功采集了含氧深海深海粘土。对这些独特和罕见样品的初步超转录组学分析表明，超转录组学方法可以成功地应用于这些深海粘土的好氧微生物群落。因此，我们建议将这种方法应用于来自四个地点的300个样本的高水平复制。这一努力将使我们能够以前所未有的统计支持来检验关于海底细胞活动的假设。我们将确定支持深海粘土长期生存的有氧代谢，确定海底好氧和厌氧群落的生存策略，并表征分泌体及其有机物降解的潜力。这将解决以下问题：在有氧条件下，生命如何在地质时间尺度上存活于地下？在有氧和无氧条件下，促进细胞长期存活的普遍和独特的机制是什么？在好氧和厌氧条件下，沉积物深度和有机质有效性对微生物胞外水解酶的产生有什么影响？这将使我们更好地了解微生物活动在海底的分布以及深层生物圈在生物地球化学循环中的作用，并提高我们对极端能量限制下生命如何在地质时间尺度上生存的理解。

Marine sediments are estimated to contain >10^29 microbial cells, which extend as far as 2,500 meters below the seafloor (mbsf). Microbial cells in these very stable and ancient settings catabolize up to one million times more slowly than model organisms in nutrient-rich cultures and are estimated to grow on millennial-timescales rather than hours to days. Because of the extremely low rates of activity, it is challenging to study the specific activities of subseafloor microbes. However, the transcriptional activity of subseafloor microbial communities can now be studied via metatranscriptomics, i.e. applying high-throughput DNA sequencing to actively transcribed message RNA (mRNA) extracted from sediment samples. Abyssal clays exhibit oxygen penetration to basement, which is due to low sedimentation rates in the ultra-oligotrophic ocean. Oxygen consumption is driven by slowly respiring microbial communities, whose cell numbers and rates of respiration are kept extremely low by low amounts of organic matter deposited from the overlying ultra oligotrophic ocean. The cellular mechanisms underlying the long-term subsistence of these aerobic microbial communities remain unknown. In 2014, an expedition to the North Atlantic successfully cored oxygenated deep-sea abyssal clay. Preliminary metatranscriptomic analyses of these unique and rare samples demonstrate that the metatranscriptomic approach can be successfully applied to the aerobic microbial communities in these abyssal clays. We thus propose to apply this method with a high level of replication, in 300 samples from four locations. This effort will enable us to test hypotheses regarding subsefloor cellular activities with unprecedented statistical support. We will determine aerobic metabolism supporting long-term subsistence in abyssal clay, identify subsistence strategies in aerobic and anaerobic subseafloor communities, and characterize secretomes and their potential for organic matter degradation. This will address the questions: How does life survive in the subsurface over geological timescales under aerobic conditions? What are the ubiquitous and unique mechanisms promoting long-term cellular survival under aerobic and anaerobic conditions? What are the effects of sediment depth, and organic matter availability, on microbial production of extracellular hydrolases under aerobic and anaerobic conditions? This will provide a better understanding of how microbial activities are distributed in the subseafloor and the deep biospheres role in biogeochemical cycles, as well as improve our understanding of how life survives over geological timescales under extreme energy limitation.