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

Eleanor E Jackson,Anne D Jungblut,Ian Hawes

doi:10.1007/s00300-021-02843-2

Eleanor E Jackson, Anne D Jungblut + Show 1 more

Open Access

https://doi.org/10.1007/s00300-021-02843-2

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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.

Highlights

Microbial mats are horizontally stratified biofilms, typically comprising Bacteria and protists often embedded in a polymeric matrix, within which steep physicochemical gradients are formed
We examine within- and between-pond variability and produce the first 18S rRNA gene high-throughput sequencing report for the McMurdo Ice Shelf, Antarctica
The Bacteria and Archaea components were dominated by Cyanobacteria and Proteobacteria, which agrees with previous studies on polar microbial mats using 16S rRNA gene surveys and metagenomics (Varin et al 2010; Kleinteich et al 2017; Dillon et al 2020a, b)

Summary

Introduction

Microbial mats are horizontally stratified biofilms, typically comprising Bacteria and protists often embedded in a polymeric matrix, within which steep physicochemical gradients are formed. Across a wide range of environments, similar biological stratifications emerge, with oxygenic phototrophs dominating the upper (illuminated, oxic) parts of the mat structure, giving way to anoxygenic production and heterotrophic aerobic and anaerobic processes with increasing. Studies have captured the bacterial diversity of many extreme environments, including the Polar Regions, the relative importance of selective and neutral processes to community assembly, for Bacteria, Archaea and Eukaryotes, is still not well understood. It is important, for understanding biodiversity in extreme environments, and for Antarctica, with the potential acceleration of environmental change that may accompany polar warming (Cowan and Tow 2004; Kennicutt et al 2014; IPCC 2019)

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