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高压下的“压球”（深海的体积在水深1000米或压力10兆帕时），依靠从水面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（细菌和古细菌），细菌和古细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体，因此对海洋生产力非常重要，例如，渔业。但我们对深海原核生物多样性和生态系统功能的认识还很有限。随着捕鱼、采矿、石油和天然气勘探越来越多地发生在更深的水域，我们迫切需要提高我们对深海生态系统功能的理解，以便适当评估这些活动和影响的社会和经济影响，并确保为子孙后代充分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的了解有限的主要原因在于它的不可接近性与深海生物减压和深海生物地球化学过程的敏感性相结合。例如，压力对细菌的生理或生长速度以及微生物进行的许多生物地球化学过程都有重大影响。因此，有意义的实验必须在原地压力下进行，这造成了重大的财政和技术限制。远程操作车辆使我们能够在深海海底进行实验研究，但是尽管现在已经成为可能，这仍然是非常危险和资源密集型的，需要复杂的深海ROV，由大型船只上的大量船员操作（例如，11名技术人员伴随着法国深海ROV VICTOR 6000的部署，需要一艘大型研究船来容纳和部署它），迄今为止，这样的系统很少可用。此外，在大多数情况下，样品在检索时遭受减压，从而阻止了进一步的实验。由于许多深海微生物可能只能在不减压的情况下进行培养，这可能解释了为什么目前只有不到1%的深海原核生物在培养中。在这里，我们建议开发一种灵活的，具有成本效益的替代原位实验：一种压力取样，实验和培养系统，可以在任何具有取样能力的中型海洋研究船的环境或操纵压力，温度和氧气条件下研究深海原核生物多样性和活动，以及生态系统功能。此外，从取样到培养的恒定高压条件克服了与减压有关的原位实验的限制。这种多重高压灭菌取芯和实验系统（MAC-EXP）将提供系统地测试环境参数（如压力、氧气可用性或pH值）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。该系统还将使海洋生物发现领域的开创性工作成为可能：来自海洋微生物的次级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会产生具有生物活性和不寻常的次生代谢物。但是，还没有研究过适应压力的细菌物种的次生代谢物，而提出的加压取样系统为进行此类研究提供了可能性。

Most deep-sea organisms live under high pressure in the "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 conduct. 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, preventing further experimentation. As many deep-sea microorgansims may only be culturable without depressurization, this may explain why less than 1 % of deep-sea prokaryotes are currently in culture. 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 activity, 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 conditions 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.