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

• Published in: Microbiome
• Main Authors: Pratibha Panwar, Michelle A. Allen, Timothy J. Williams, Alyce M. Hancock, Sarah Brazendale, James Bevington, Simon Roux, David Páez-Espino, Stephen Nayfach, Maureen Berg, Frederik Schulz, I-Min A. Chen, Marcel Huntemann, Nicole Shapiro, Nikos C. Kyrpides, Tanja Woyke, Emiley A. Eloe-Fadrosh, Ricardo Cavicchioli
• Format: Article in Journal/Newspaper
• Language: English
• Published: BMC 2020
• Subjects: Antarctic microbiology; Polar light cycle; Metagenome time series; Host-virus interactions; Meromictic lake; Microbial food web; Microbial ecology; QR100-130; Antarctic; Southern Ocean; East Antarctica; Vestfold Hills; Vestfold; Ace Lake; Antarc*; Antarctica
• Online Access: https://doi.org/10.1186/s40168-020-00889-8; https://doaj.org/article/deb2697ed2be469198ad3fe37eae0a3b

Abstract 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 ...