High-resolution genomics to reveal changes in microbial biodiversity across space and time in the warming Arctic Ocean

北极是地球上受全球变暖影响最大的生态系统。因此，它是全球变化后果的风向标，因此也是我们星球上生物多样性持续存在的风向标。然而，由于进入北极的后勤挑战，北极，特别是北冰洋中部，仍然是地球上最不了解的生物群落之一。此外，随着北极环境变化的加速，北极不仅具有调节全球气候的作用，而且还被用于提取生物和地质资源，已成为地缘政治利益的主要焦点。因此，北极在生物多样性方面提供了重要的生态系统服务，这在很大程度上是未知的，特别是在最难以进入的地理区域，如北冰洋中部。因此，了解北极最大的水生生态系统如何变化对21世纪的不同关键学科至关重要，包括气候研究、保护和可持续经济发展。海冰和海水中的水生微生物在气候反馈和维持食物网（海洋初级生产）方面发挥着关键作用，而食物网是保护和生态系统服务的核心。由于微生物对环境变化的快速适应反应，它们也可以作为生物指标。尽管基因组学方法已经为微生物群落对环境变化的响应提供了变革性的见解，但其在极地生态系统中的应用受到限制，特别是在北冰洋中部，这主要是由于该生态系统的获取问题和极端性质。为了克服这些挑战，2020年开展了北极气候研究多学科漂流观测站（MOSAiC）。MOSAiC是历史上规模最大的极地探险，包括20多个国家和400多名研究人员，研究漂流的表面栖息地，同时通过跨极漂流流穿越北冰洋中部。因此，破冰船“北极星号”花了一年的时间漂流穿过北冰洋中部，并被困在海冰中。因此，这次探险第一次能够对同样的表层海洋栖息地（主要是海冰和直接在其下共同漂流的水）进行采样，同时它被跨极地漂流流带过北冰洋。因此，MOSAiC漂流探险创造了一个时间序列的样本，反映了漂流表面海洋栖息地（例如，海冰从形成到融化）环境变化的季节周期，这是前所未有的，但将有助于揭示北冰洋环境变化如何影响北极气候系统。这个新的NERC项目不仅建立在独特的时间序列数据和样本上，它还利用了随后由美国能源部联合基因组研究所（JGI， USA）资助的微生物基因组学项目。后者为来自漂流海冰的400多个时间序列样本提供序列数据，包括微生物宏基因组和亚转录组的基本分析（如组装、注释）。定制的生物信息学和群落生态学分析将应用于这些序列数据，以揭示海洋微生物及其微生物组的栖息地特异性基因组多样性如何随时间（完整的季节周期）变化，以及与变化的栖息地特征（例如，秋季海冰的形成和春季和夏季的融化）的关系。因此，该项目将为评估微生物作为生物领头羊如何应对不断变化的北冰洋提供一个基线，这对于预测北极变暖如何影响由微生物支撑的生态系统服务（如维持海洋食物网和驱动北冰洋的碳循环）至关重要。

The Arctic is the most impacted ecosystem on Earth by global warming. Thus, it serves as a bellwether for the consequences of global change and therefore the persistence of biodiversity on our planet. Yet, due to logistical challenges to access, the Arctic and especially the central Arctic Ocean, remains one of the most poorly understood biomes on Earth. Moreover, as the environmental change in the Arctic is accelerating, it has become the main focus of geopolitical interests because the Arctic is not only regulating global climate but is used for extracting biological and geological resources. Thus, the Arctic provides significant ecosystem services on biodiversity that is largely unknown, particularly for the most inaccessible geographic areas such as the central Arctic Ocean. Understanding how the largest of all aquatic ecosystems in the Arctic changes is therefore crucial for different key disciplines of the 21st century including climate research, conservation, and sustainable economic development. Aquatic microbes in sea ice and seawater play pivotal roles in climate feedbacks and in sustaining food webs (marine primary production), which are central for conservation and ecosystem services. Microbes also serve as biological indicators due to their fast adaptive response following environmental change. Although genomic approaches have provided transformative insights into responses of microbial communities to environmental change, their application is limited in polar ecosystems and especially the central Arctic Ocean mainly due to issues of access and the extreme nature of this ecosystem. To overcome these challenges, a Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) has been conducted in 2020. MOSAiC is the largest polar expedition in history including over 20 countries with more than 400 researchers, studying a drifting surface habitat while it crosses the central Arctic Ocean via the transpolar drift current. Hence, the ice-breaker RV 'Polarstern' spent a year drifting across the central Arctic Ocean and locked up into the sea ice. This expedition, therefore, enabled for the first time to sample the same surface-ocean habitat (mainly sea ice and co-drifting water directly underneath) while it was carried across the Arctic Ocean by the transpolar drift current. Thus, the MOSAiC drift expedition has created a time series of samples reflecting the seasonal cycle of environmental changes in a drifting surface ocean habitat (e.g. a sea-ice floe from its formation to thaw), which is unprecedented but will help to reveal how the environmental change in the Arctic Ocean impacts the Arctic climate system. This new NERC project is not only built on the unique time-series data and samples, it capitalizes on a subsequent microbial genomics project funded by the DOE Joint Genome Institute (JGI, USA). The latter is providing sequence data including their basic analyses (e.g. assembly, annotations) of microbial metagenomes and metatranscriptomes for over 400 time-series samples from the drifting sea-ice floe. Bespoke bioinformatics and community ecology analyses will be applied to those sequence data for revealing how habitat-specific genomic diversity of ocean microbes and their microbiomes is changing throughout time (complete seasonal cycle) and in relation to changing habitat characteristics (e.g. formation of sea ice in autumn and thaw in spring and summer). Thus, this project will provide a baseline for assessing how microbes as a biological bellwether respond to the changing Arctic Ocean, which is essential for making predictions about how warming in the Arctic impacts ecosystem services underpinned by microbes such as sustaining the marine food web and driving the carbon cycle in the Arctic Ocean.