Aerobic microbial activity in deep sea abyssal clay

据估计，海洋沉积物含有>10^29个微生物细胞，这些细胞延伸到海底以下2，500米（mbsf）。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，并且估计以千年时间尺度而不是几小时到几天的时间生长。由于活动率极低，研究海底微生物的具体活动具有挑战性。然而，现在可以通过元转录组学研究海底微生物群落的转录活动，即对从沉积物样品中提取的活跃转录的信使RNA进行高通量DNA测序。深海粘土显示氧气渗透到基底，这是由于超贫营养海洋的低沉积速率。氧气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层超贫营养海洋沉积的少量有机物而保持极低。这些需氧微生物群落长期生存的细胞机制仍然未知。2014年，北大西洋的一次探险成功地对深海含氧的深海粘土进行了取样。这些独特的和罕见的样品的初步metatranscriptomic分析表明，metatranscriptomic的方法可以成功地应用于这些深海粘土中的好氧微生物群落。因此，我们建议应用这种方法具有高水平的复制，在300个样品从四个位置。这一努力将使我们能够测试假设subsefloor细胞活动与前所未有的统计支持。我们将确定有氧代谢支持长期生存在深海粘土，确定生存战略在有氧和厌氧海底下社区，并表征分泌物和它们的潜力有机物降解。这将解决的问题：生命如何生存在地下超过地质时间尺度在有氧条件下？在有氧和无氧条件下，促进细胞长期存活的普遍而独特的机制是什么？沉积物深度和有机质可利用性对好氧和厌氧条件下微生物产生胞外水解酶的影响是什么？这将使我们更好地了解微生物活动如何在海底分布以及深层生物圈在生物地球化学循环中的作用，并提高我们对生命如何在极端能源限制下在地质时间尺度上生存的了解。

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.