Tapping into the virome of glaciers and ice sheets

只是在过去10年里，对冰川栖息地的微生物调查才发现，冰川应该被视为地球生物圈的一部分，因为它们拥有活跃的微生物群落，这些微生物群落调节着重要的营养转化，如碳固定、铁循环和甲烷的产生，这些变化在当地乃至全球范围内都很重要。不同的冰川成分为微生物群落提供了不同的栖息地(和挑战)。例如，在夏季，冰川表面可以获得大量的融化水，并为微生物定居创造了几个栖息地。平均而言，在每升海水中发现了惊人的100亿个病毒颗粒。最近，我们自己的数据显示，病毒在冰川表面也是丰富和动态的。事实上，我们最近认为，低温栖息地是病毒驱动的微生物进化的热点。冰川表面的病毒对细菌群落造成重大死亡，因此，它们对这些栖息地的营养循环具有重要影响。此外，病毒以两种方式影响细菌群落：它们控制细菌总数，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，它们是宿主特有的)。当宿主数量丰富时，感染它的病毒也会变得丰富，最终导致宿主种群崩溃。病毒可以将遗传物质从一个宿主细胞带到另一个宿主细胞，其中一些病毒甚至可以在宿主体内存活并改变其特性，而不会实际杀死它们。通过这种方式，它们在宿主的进化和遗传多样性中扮演着非常重要的角色。令人惊讶的是，人们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分离和表征它们的遗传物质来探索，这些遗传物质是直接从环境中回收的，使用元基因组学方法。每个被分析的冰川栖息地样本代表了不同病毒类型的复杂混合物的快照。在这个项目中，我们将获得斯瓦尔巴群岛3个小山谷冰川表面和格陵兰冰盖50公里横断面上的病毒群落的图片。尽管病毒多样性在当地范围内可能非常高，但我们想测试在两个北极环境中是否都存在许多相同的病毒，以及它们与来自其他环境(包括寒冷和温暖的地区、淡水和海洋、其他极端栖息地)的病毒相比如何。有必要了解低温生境中的病毒多样性，特别是相对孤立的系统中的病毒多样性，以证明这些系统中的微生物多样性出人意料地高，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的基因。在地理上，冰川和冰盖覆盖了约1500万平方公里，或约占地球陆地表面积的10%。在冰川盛期，这一覆盖率要高得多。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。考虑到世界各地的冰川和冰盖正在退缩，特别是在阿尔卑斯山和北极地区，迫切需要了解冰川和冰盖生物群的遗传多样性及其独特特征。

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.