Antarctica – what it takes to get down and back out of the rabbit hole

Three Antarctic expeditions spanning 10 years, sampling through winter for a total of 18 months, and 3 dedicated years of bioinformatics analysis – we’ve finally learned the well kept secrets of Antarctica’s, Ace Lake microbes.
Published in Microbiology
Antarctica – what it takes to get down and back out of the rabbit hole

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BioMed Central
BioMed Central BioMed Central

Influence of the polar light cycle on seasonal dynamics of an Antarctic lake microbial community - Microbiome

Background 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. Results 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. Conclusion 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

The paper in Microbiome is here: Influence of the polar light cycle on seasonal dynamics of an Antarctic lake microbial community

To start with, this is what we do and why: 

Rick Cavicchioli’s group studies Antarctic microorganisms, discovering which types live in and around Antarctica, learning how they evolve and grow in the cold, and assessing how they are likely to respond to ecosystem changes, including climate change. 

The research is important because environmental microbes enable all other life forms on Earth to exist, and the vast majority of life on the planet grows at low temperatures. 

And where exactly do we do the work? Ace Lake, Vestfold Hills, East Antarctica – take a look:

Our first expedition to Ace Lake was the summer of 2006 – note Antarctica is in the southern hemisphere so December – February is summer.

The third expedition was the big one: 2013 – 2015.
2013 – 2015: Alyce Hancock and Sarah Payne spent 18 months taking samples in Antarctica.
Summer to summer sampling.
A complete seasonal cycle of samples.

Then, after several years for DNA extractions by Tim Williams and sequencing by JGI, Pratibha Panwar performed three solid years of analysis as the core of her PhD studies.

Pratibha hard at work.

Pratibha analysed 120 metagenomes → 20 Gbp of data → 25 million assembled contigs → 40 million protein-coding genes.

Years of Research Associate hours were also poured into the project by Michelle Allen and Tim Williams. Co-assemblies, rhodopsins, food webs.
All underpinned by dedicated efforts of JGI scientists who have collaborated for over 20 years.

And the outcome.

You may like to start with the publicity video, which is also available on Vimeo.

Then the article.

And check out the movie in supplementary information and look for this….!?

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