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

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 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.

Genome Analysis of a Verrucomicrobial Endosymbiont With a Tiny Genome Discovered in an Antarctic Lake

“…Microbial biomass was obtained and field observations recorded from lakes in the Vestfold Hills, Antarctica (Supplementary Figure 1). Sampling at Organic Lake was performed by sequential size fractionation through a 20-µm prefilter onto 3.0-, 0.8-, and 0.1-µm large-format membrane-filters (293 mm diameter polyethersulfone), samples preserved and DNA extracted, as described previously (Yau et al, 2011(Yau et al, , 2013Tschitschko et al, 2018;Panwar et al, 2020).…”

Quantification of the covariation of lake microbiomes and environmental variables using a machine learning‐based framework

“…In principle, both the covariation framework as well as the bioindicator analysis can easily be applied to samples from different environmental sources and other sequencing methods, such as metagenomic and metatranscriptomic data sets, as long as there is a straightforward interpretation for the results of the IndVal method. This is especially noteworthy as the importance and popularity of metagenomic assays in microbial ecology has risen fast in the last years (Awasthi et al, 2020; Hugerth et al, 2015; Panwar et al, 2020; Vishnivetskaya et al, 2020; Zeng et al, 2016).…”

Linking Genomic and Physiological Characteristics of Psychrophilic Arthrobacter to Metagenomic Data to Explain Global Environmental Distribution

“…Metagenomic analyses have also begun to be used to uncover the ways in which communities in polar environments respond to changing environmental conditions; for example, the effects of the seasonal polar sunlight cycle on Antarctic marine and marine-derived lake communities [10,11], and the roles that Arctic bacteria play in melting permafrost acting as a CO 2 source and atmospheric CH 4 sink [12,13].…”