School of Biotechnology and Biomolecular Sciences, UNSW Sydney, Sydney, New South Wales, 2052, Australia.
Institute for Marine and Antarctic Studies, University of Tasmania, 20 Castray Esplanade, Battery Point, Tasmania, Australia.
Microbiome. 2020 Aug 9;8(1):116. doi: 10.1186/s40168-020-00889-8.
Cold environments dominate the Earth's biosphere and microbial activity drives ecosystem processes thereby contributing greatly to global biogeochemical cycles. Polar environments differ to all other cold environments by experiencing 24-h sunlight in summer and no sunlight in winter. The Vestfold Hills in East Antarctica contains hundreds of lakes that have evolved from a marine origin only 3000-7000 years ago. Ace Lake is a meromictic (stratified) lake from this region that has been intensively studied since the 1970s. Here, a total of 120 metagenomes representing a seasonal cycle and four summers spanning a 10-year period were analyzed to determine the effects of the polar light cycle on microbial-driven nutrient cycles.
The lake system is characterized by complex sulfur and hydrogen cycling, especially in the anoxic layers, with multiple mechanisms for the breakdown of biopolymers present throughout the water column. The two most abundant taxa are phototrophs (green sulfur bacteria and cyanobacteria) that are highly influenced by the seasonal availability of sunlight. The extent of the Chlorobium biomass thriving at the interface in summer was captured in underwater video footage. The Chlorobium abundance dropped from up to 83% in summer to 6% in winter and 1% in spring, before rebounding to high levels. Predicted Chlorobium viruses and cyanophage were also abundant, but their levels did not negatively correlate with their hosts.
Over-wintering expeditions in Antarctica are logistically challenging, meaning insight into winter processes has been inferred from limited data. Here, we found that in contrast to chemolithoautotrophic carbon fixation potential of Southern Ocean Thaumarchaeota, this marine-derived lake evolved a reliance on photosynthesis. While viruses associated with phototrophs also have high seasonal abundance, the negative impact of viral infection on host growth appeared to be limited. The microbial community as a whole appears to have developed a capacity to generate biomass and remineralize nutrients, sufficient to sustain itself between two rounds of sunlight-driven summer-activity. In addition, this unique metagenome dataset provides considerable opportunity for future interrogation of eukaryotes and their viruses, abundant uncharacterized taxa (i.e. dark matter), and for testing hypotheses about endemic species in polar aquatic ecosystems. Video Abstract.
冷环境主导着地球的生物圈，微生物活动驱动着生态系统过程，从而对全球生物地球化学循环做出了巨大贡献。极地环境与所有其他冷环境不同，因为它们在夏季有 24 小时的阳光，而在冬季则没有阳光。南极洲东部的沃尔夫山脉拥有数百个湖泊，这些湖泊仅在 3000-7000 年前才从海洋起源演变而来。Ace 湖是该地区的一个分层湖，自 20 世纪 70 年代以来一直受到深入研究。在这里，总共分析了 120 个宏基因组，代表了一个季节性周期和四个跨越 10 年的夏季，以确定极地光周期对微生物驱动的营养循环的影响。
该湖系统的特点是复杂的硫和氢循环，特别是在缺氧层，在水柱中存在多种生物聚合物分解的机制。两个最丰富的类群是光养生物（绿硫细菌和蓝细菌），它们受到季节性阳光供应的高度影响。在夏季，在界面处茁壮成长的 Chlorobium 生物量的程度在水下视频中被捕捉到。Chlorobium 的丰度从夏季的高达 83%下降到冬季的 6%和春季的 1%，然后反弹到高水平。预测的 Chlorobium 病毒和蓝藻噬菌体也很丰富，但它们的水平与宿主没有负相关。
在南极洲进行越冬探险在后勤上具有挑战性，这意味着对冬季过程的了解只能从有限的数据中推断出来。在这里，我们发现，与南大洋 Thaumarchaeota 的化能自养碳固定潜力相反，这个海洋衍生的湖泊演变出了对光合作用的依赖。虽然与光养生物相关的病毒也具有高季节性丰度，但病毒感染对宿主生长的负面影响似乎是有限的。整个微生物群落似乎已经发展出产生生物量和再矿化养分的能力，足以在两轮阳光驱动的夏季活动之间维持自身。此外，这个独特的宏基因组数据集为未来研究真核生物及其病毒、丰富的未被描述的类群（即暗物质）以及测试关于极地水生生态系统特有物种的假设提供了巨大的机会。视频摘要。
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