Hidden biofilms in a far northern lake and implications for the changing Arctic

Abstract

Shallow lakes are common across the Arctic landscape and their ecosystem productivity is often dominated by benthic, cyanobacterial biofilms. Many of these water bodies freeze to the bottom and are biologically inactive during winter, but full freeze-up is becoming less common with Arctic warming. Here we analyzed the microbiome structure of newly discovered biofilms at the deepest site of a perennially ice-covered High Arctic lake as a model of polar microbial communities that remain unfrozen throughout the year. Biofilms were also sampled from the lake’s shallow moat region that melts out and refreezes to the bottom annually. Using high throughput small subunit ribosomal RNA sequencing, we found more taxonomic richness in Bacteria, Archaea and microbial eukaryotes in the perennially unfrozen biofilms compared to moat communities. The deep communities contained both aerobic and anaerobic taxa including denitrifiers, sulfate reducers, and methanogenic Archaea. The water overlying the deep biofilms was well oxygenated in mid-summer but almost devoid of oxygen in spring, indicating anoxia during winter. Seasonally alternating oxic-anoxic regimes may become increasingly widespread in polar biofilms as fewer lakes and ponds freeze to the bottom, favoring prolonged anaerobic metabolism and greenhouse gas production during winter darkness.

Pole-to-Pole Connections: Similarities between Arctic and Antarctic Microbiomes and Their Vulnerability to Environmental Change

“…We conclude that the microbiota of both polar regions may be more connected than previously assumed and our data suggest a biogeographical connection between both poles, consistent with some previous studies Jungblut et al, 2010;Chrismas et al, 2015;Cox et al, 2016;Biersma et al, 2017;Mohit et al, 2017). The polar microbial communities in our study are an assemblage of ubiquitously-distributed and potentially endemic taxa.…”

“…These findings suggest that the global dispersal of certain (microbial) species is combined with environmental selection shaping bacterial communities in the polar regions (Vyverman et al, 2010;Chong et al, 2015;Cox et al, 2016), though temporal (Rochera et al, 2010) or spatial (Villaescusa et al, 2013) variability in environmental conditions can cause differences among prokaryotic meta-communities in polar habitats. Highly seasonal conditions in the polar regions (Chong et al, 2015), such as the absence of light in winter (Alonso-Saez et al, 2012) freezing and limited freshwater availability Mohit et al, 2017) and low temperatures (Yergeau et al, 2007(Yergeau et al, , 2012Kleinteich et al, 2012) may cause the observed differences between polar and non-polar communities, since non-polar regions exhibit more moderate environmental conditions. In fact, large differences in temperature and annual solar radiation but not regional precipitation explained community differences in the present dataset.…”

“…The harsh conditions prevent the survival of most macroorganisms but allow diverse microbial life to thrive and dominate (Vincent, 2000a;Vincent and Quesada, 2012). A common group of microbial communities found in the terrestrial and lacustrine environments of both polar regions are those forming "macro-biofilms, " which are highly organized structures which can have vertical differentiation of functional and physiological assemblages (Fernández-Valiente et al, 2007;Mohit et al, 2017).…”

Microbial genomes retrieved from High Arctic lake sediments encode for adaptation to cold and oligotrophic environments

“…To date, culture-independent studies of microbial communities in Arctic lakes have been most 50 often performed by amplifying and sequencing taxonomic markers like the 16S rRNA gene (e.g., 51 Crump et al, 2012;Mohit et al, 2017;Ruuskanen et al, 2018;Stoeva et al, 2014;Wang et al, 2016Wang et al, , 52 2019). However, amplicon-based methods are subject to PCR amplification bias, which might alter the 53 estimates of microbial community composition and diversity.…”

Photoecology of the Antarctic cyanobacterium Leptolyngbya sp. BC1307 brought to light through community analysis, comparative genomics and in vitro photophysiology

“…Cyanobacterial mats are found in both the depths of lakes and their shallow moats (Jungblut et al, ; Mohit, Culley, Lovejoy, Bouchard, & Vincent, ; Zhang et al, ). Deep mats are distinctly laminated, sometimes forming large pinnacles, while those at lake margins and in shallow pools are less structurally complex.…”