MAC-EXP: Development of a pressurised sampling, experimentation and cultivation system for deep-sea sediments

大多数深海生物生活在所谓的压力圈(1000米水深的深海体积或10兆帕压力)的高压下，依靠从表层水域下沉的有机颗粒作为食物。到目前为止，海洋沉积物中最丰富的生物是原核生物(细菌和古生菌)，细菌和古生菌的生物量如此之大，以至于它们被认为是有机物再矿化的主要媒介，这一过程将营养物质释放回水柱，因此对海洋生产力和例如渔业非常重要。但我们对深海原核生物多样性和生态系统功能的了解很少。随着捕捞、采矿、石油和天然气勘探越来越多地在较深水域进行，我们迫切需要提高对深海生态系统功能的了解，以便适当评估这类活动和影响的社会和经济影响，并确保为子孙后代适当管理深海生物多样性和自然资源。不幸的是，这并不容易：我们对深海生物多样性和生态系统功能了解有限的主要原因在于它难以获得，而且对深海生物和深海生物地球化学过程的降压敏感。例如，压力对细菌生理或生长速度以及微生物参与的许多生物地球化学过程都有重大影响。因此，必须在现场压力下进行有意义的实验，这导致了重大的资金和技术限制。遥控潜水器使我们能够在深海海底进行实验研究，但虽然现在有可能，但这仍然是非常危险和资源密集型的，需要复杂的深海ROV，由大型船只上的大型船员操作(例如，11名技术人员陪同部署法国深海ROV Victor 6000；需要一艘大型科考船来容纳和部署它)，而且到目前为止，这样的系统很少。此外，在大多数情况下，样品在取回时会发生降压。由于许多深海微生物可能只有在没有降压的情况下才能培养，这可能解释了为什么目前只有不到1%的深海原核生物可以培养。在这里，我们建议开发一种灵活、经济高效的替代现场实验的方法：压力取心、实验和培养系统，该系统能够在任何具有取心能力的中型远洋考察船上，在常压或操纵的压力、温度和氧气条件下，研究深海原核生物的生物多样性和生态系统功能。此外，从采样到培养的恒定高压链克服了与降压相关的现场实验的局限性。这种多蒸压取芯和实验系统(MAC-EXP)将提供系统地测试环境参数，如压力、氧气可用性或pH对深海生物及其生物化学的影响，以及对生物地球化学和地质微生物过程的速率和途径的影响。该系统还将允许在海洋生物发现领域开展开创性工作：来自海洋微生物的次生代谢物是化学多样性的丰富来源，几种海洋微生物衍生的化合物目前正在进行临床试验。最近的证据表明，深海沉积物中的压力适应细菌产生具有生物活性的不寻常的次生代谢物。但是，从来没有对适应压力的细菌物种的次生代谢产物进行过调查，拟议的加压采样系统提供了进行此类研究的可能性。

Most deep-sea organisms live under high pressure in the so-called piezosphere (the volume of the deep-sea at > 1000 m of water depth or > 10MPa pressure) and depend on organic particles sinking down from the surface waters for food. The most abundant organisms by far in marine sediments are prokaryotes (bacteria and archaea), and the biomass of the bacteria and archaea is so great that they are thought to be the main agents of the remineralisation of organic matter, a process which releases nutrients back into the water column and is thus very important for ocean productivity and, for example, fisheries. But our knowledge of deep-sea prokaryote diversity and ecosystem function is scarce. With fishing, mining, oil and gas exploration increasingly taking place in deeper waters, we urgently need to improve our understanding of the functioning of deep-sea ecosystems in order to assess appropriately the societal and economic implications of such activities and impacts and to ensure adequate management of deep-sea biodiversity and natural resources for future generations.Unfortunately, this is not easy: the main reasons for our limited knowledge of deep-sea biodiversity and ecosystem functioning lies in the combination of its inaccessibility with the sensitivity to depressurization of deep-sea organisms and deep-sea biogeochemical processes. Pressure has significant effects on, for example, bacterial physiology or growth rates, as well as many biogeochemical processes that microorganisms are involved in. In consequence, meaningful experimentation has to be carried out under in situ pressure, which results in major financial and technical constraints. Remotely Operated Vehicles allow us to conduct experimental research at the deep-sea floor, but although now possible, this is still very risky and resource-intensive, requiring sophisticated deep-sea ROVs, operated by large crews from large vessels (e.g. 11 technical staff accompany a deployment of the French deep-sea ROV VICTOR 6000; and a large research ship is needed to accommodate and deploy it), and to-date very few such systems are available. In addition, samples in most cases suffer depressurization upon retrieval. As many deep-sea microorgansims may only be culturable without depressurization, this may explain why less than 1 % of deep-sea prokaryotes can currently be cultured. Here we propose to develop a flexible, cost-effective alternative to in situ experimentation: a pressure-coring, experimentation and cultivation system that enables studies of deep-sea prokaryote biodiversity and ecosystem functioning, under ambient or manipulated pressure, temperature and oxygen conditions from any medium sized ocean going research ship with coring capability. In addition, the constant high pressure chain from sampling to culture overcomes limitations of in situ experiments related to depressurisation.This Multiple-Autoclave-Coring and Experimentation system (MAC-EXP) will provide the possibility to systematically test the influence of environmental parameters, such as pressure, oxygen availability or pH on deep-sea organisms and their biochemistry, as well as on rates and pathways of biogeochemical and geomicrobial processes. The system will also allow pioneering work in the field of marine biodiscovery: secondary metabolites from marine microorganisms are a rich source of chemical diversity and several marine-microbe derived compounds are now in clinical trials. Recent evidence shows that pressure-adapted bacteria from deep-sea sediments produce biologically active and unusual secondary metabolites. But no pressure-adapted bacterial species have ever been investigated for their secondary metabolites and the proposed pressurised sampling system provides the possibility to conduct such studies.