16S rRNA gene and 18S rRNA gene diversity in microbial mat communities in meltwater ponds on the McMurdo Ice Shelf, Antarctica

Abstract

The undulating ice of the McMurdo Ice Shelf, Southern Victoria Land, supports one of the largest networks of ice-based, multiyear meltwater pond habitats in Antarctica, where microbial mats are abundant and contribute most of the biomass and biodiversity. We used 16S rRNA and 18S rRNA gene high-throughput sequencing to compare variance of the community structure in microbial mats within and between ponds with different salinities and pH. Proteobacteria and Cyanobacteria were the most abundant phyla, and composition at OTU level was highly specific for the meltwater ponds with strong community sorting along the salinity gradient. Our study provides the first detailed evaluation of eukaryote communities for the McMurdo Ice Shelf using the 18S rRNA gene. They were dominated by Ochrophyta, Chlorophyta and Ciliophora, consistent with previous microscopic analyses, but many OTUs belonging to less well-described heterotrophic protists from Antarctic ice shelves were also identified including Amoebozoa, Rhizaria and Labyrinthulea. Comparison of 16S and 18S rRNA gene communities showed that the Eukaryotes had lower richness and greater similarity between ponds in comparison with Bacteria and Archaea communities on the McMurdo Ice shelf. While there was a weak correlation between community dissimilarity and geographic distance, the congruity of microbial assemblages within ponds, especially for Bacteria and Archaea, implies strong habitat filtering in ice shelf meltwater pond ecosystems, especially due to salinity. These findings help to understand processes that are important in sustaining biodiversity and the impact of climate change on ice-based aquatic habitats in Antarctica.

Microbial Community Composition of the Antarctic Ecosystems: Review of the Bacteria, Fungi, and Archaea Identified through an NGS-Based Metagenomics Approach

“…In a study comparing McMurdo Dry Valleys' microbial mat communities exposed to different environmental factors, salinity was the best predictor for community composition, followed by temperature and pH [107]. More specifically, Cyanobacteria dominated the mats in high salinity ponds, with Pseudanabaenales replacing Phormidiaceae as the dominant family in these conditions.…”

“…Thus, Cyanobacteria provide substrates and nutrients for the rest of the community, which in turn are capable of degrading those compounds. However, multiple studies of the Antarctic mats show that Proteobacteria (mostly Alphaproteobacteria and Betaproteobacteria) and Bacteroidetes are often equally found, if not more abundant [7,[107][108][109][110]. In fact, a study comparing the Artic and Antarctic bacterial mats revealed the same high abundance of Proteobacteria on both poles and similar overall community composition [110].…”

“…A comparative study of the mats in different ponds in the McMurdo Dry Valleys based on both 16S and 18S sequencing found that eukaryotes had lower community richness and less diversity between sample sites compared to bacteria and archaea [107]. There was also a strong correlation between bacteria and archaea communities, pointing to either speciesspecific interactions within these groups or habitat filtering leading to high homogeneity across the ponds.…”

Lipid Biomarkers From Microbial Mats on the McMurdo Ice Shelf, Antarctica: Signatures for Life in the Cryosphere

“…Metagenomic and small subunit rRNA gene studies have confirmed microscopy surveys identifying diverse and highly productive cyanobacterial communities in the 'dirty ice' of the McMurdo Ice Shelf (Varin et al, 2012;Jackson et al, 2021). Major taxa comprise the heterocyte forming genera Anabaena, Nostoc, and Nodularia and filamentous non-heterocyte forming genera including Oscillatoria, Phormidium, Pseudanabaena, and Leptolyngbya (Jungblut et al, 2005;Varin et al, 2012;Jackson et al, 2021).…”

Insight Into Ecology, Metabolic Potential, and the Taxonomic Composition of Bacterial Communities in the Periodic Water Pond on King George Island (Antarctica)

“…To date, studies of Antarctic ponds have given insight into the structure of communities forming dense microbiological mats (Fernández-Valiente et al, 2001;Peeters et al, 2011Peeters et al, , 2012Sutherland et al, 2020;Jackson et al, 2021), lining mats of benthic zone and sediments (Archer et al, 2015;Callejas et al, 2018), and phytoplankton (Vinocur and Unrein, 2000;Allende and Mataloni, 2013;Archer et al, 2014). A limited study was conducted to characterize microbial communities in water columns (Archer et al, 2016) and determine their metabolic properties (Ferrés et al, 2015).…”