Tapping into the virome of glaciers and ice sheets

只是在过去10年里，对冰川生境的微生物调查才揭示，冰川应被视为地球生物圈的一部分，因为冰川中有活跃的微生物群落，它们介导重要的营养转化，如固碳、铁循环和甲烷的产生，这些在地方和潜在的全球范围内都很重要。冰川的不同组成部分为微生物群落提供了不同的栖息地（和挑战）。例如，在夏季，大量的融水在冰川表面变得可用，并为微生物的殖民创造了几个栖息地。平均而言，每升海水中发现了惊人的100亿个病毒颗粒。最近，我们自己的数据表明，冰川表面的病毒也很丰富，而且是动态的。事实上，我们最近提出，低温栖息地是病毒驱动下微生物进化的热点。冰川表面的病毒对细菌群落造成了显著的死亡，因此，它们对这些栖息地的营养物质循环产生了重要影响。此外，病毒以两种方式影响细菌群落：它们控制它们的总数，它们还影响群落中存在的类型。许多病毒被认为只感染一种特定的宿主（即，它们是宿主特异性的）。当宿主大量存在时，感染它的病毒也会变得大量存在，最终导致宿主种群的崩溃。病毒可以将遗传物质从一个宿主细胞携带到另一个宿主细胞，其中一些甚至可以在宿主中持续存在并改变其特性，而不会真正杀死它们。因此，它们在宿主的进化和遗传多样性中起着非常重要的作用。令人惊讶的是，对冰川栖息地病毒的遗传多样性一无所知。冰川病毒群落的组成和代谢潜力可以通过使用宏基因组方法直接从环境中回收的遗传物质进行分离和表征来探索。分析的每个冰川栖息地样本都代表了不同病毒类型复杂混合物的快照。在这个项目中，我们将获得斯瓦尔巴特群岛3个小山谷冰川表面和格陵兰冰盖沿着50公里横断面上病毒群落的图片。虽然在局部范围内病毒多样性可能非常高，但我们想测试是否有许多相同的病毒存在于北极环境中，以及它们与其他环境（寒冷和温暖的地方，淡水和海洋，其他极端栖息地）的病毒相比如何。在低温生境中，特别是在相对孤立的系统中，病毒多样性的知识是必要的，以证明这些系统中的微生物多样性出乎意料的高，病毒基因组可能包含重要的微生物代谢基因，包括那些负责生命适应寒冷条件。在地理上，冰川和冰盖覆盖约1500万平方公里，约占地球陆地面积的10%。这一覆盖率在最大冰川期要高得多。因此，冰川和冰盖代表了地球上未被探索的遗传物质的很大一部分。考虑到全世界的冰川和冰盖正在退缩，特别是在阿尔卑斯和北极地区，迫切需要了解冰川和冰盖生物群落的遗传多样性及其独特的特征。

It is only during the last 10 years that microbial investigations of glacial habitats have revealed that glaciers should be considered as part of the Earth's biosphere, since they harbour active microbial communities that mediate important nutrient transformations such as C fixation, iron cycling and production of methane that are important at local and potentially global scales. Different components of glaciers provide different habitats (and challenges) for microbial communities. For instance, plenty of meltwater becomes available at the surface of glaciers during the summer and several habitats are created for microbial colonisation. On average, a staggering 10 billion virus particles are found in every litre of seawater. More recently, our own data have shown that viruses are both abundant and dynamic at the surface of glaciers too. In fact, we have recently argued that low temperature habitats are hot spots of microbial evolution driven by viruses. Viruses at the surface of glaciers cause significant mortality to bacterial communities and consequently, they have an important effect on the cycling of nutrients of these habitats. Further, viruses affect bacterial communities in two ways: they control their total number and they also influence which types are present in the community. Many viruses are believed infect only one specific host (i.e., they are host specific). When that host is abundant, the viruses that infect it will also become abundant, leading eventually to a crash in the host population. Viruses can carry genetic material from one host cell to another and some of them can even persist in their hosts and change their properties without actually killing them. In this way they play a very important role in the evolution and genetic diversity of their hosts. Surprisingly, nothing is known regarding the genetic diversity of viruses in glacial habitats. The composition and the metabolic potential within the glacial viral community can be explored by isolating and characterising their genetic material recovered directly from the environment using a metagenomic approach. Each sample of glacial habitat analysed represents a snapshot of the complex mixture of different viral types. In this project, we shall obtain a picture of the virus communities at the surface of 3 small valley glaciers in Svalbard and along a 50Km transect of the Greenland Ice Sheet. Although virus diversity is probably very high at a local scale, we want to test whether many of the same viruses are present in both Arctic environments and how they compare with viruses from other environments (both cold and warmer localities, freshwater and marine, other extreme habitats). Knowledge of viral diversity in low temperature habitats, particularly in relatively isolated systems, are necessary to demonstrate that microbial diversity in those systems is unexpectedly high and that virus genomes might contain important microbial metabolic genes, including those responsible for life adaptation to cold conditions. Geographically, glaciers and Ice Sheets cover ca 15 million km2, or ca 10% of Earth's land surface area. This coverage was considerably higher during periods of glacial maxima. Thus, glaciers and ice sheets represent a substantial fraction of unexplored genetic material on the planet. Considering that worldwide glaciers and ice sheets are retreating, particularly in the Alpine and Arctic regions, the understanding of the genetic diversity of the glacial and ice sheet biome and its unique features is urgent.