Characterisation of cyanobacterial mats from perennially ice-covered lakes in Antarctica

Abstract

Cyanobacteria are ubiquitous in Antarctic perennially ice-covered lakes, where they dominate the benthic landscape forming extensive microbial mats and complex stromatolite and microbialite structures. Despite their importance as primary producers and ecosystem engineers in the cryosphere, few genomic studies have focused on polar cyanobacteria to date, and many cyanobacterial microbial mat communities remain unstudied using DNA-based methods.
The research presented in this thesis aimed to characterise the diversity of cyanobacterial mat communities originating from perennially ice-covered lakes, assess the contributions of organisms towards nutrient cycling across spatial scales, and investigate the potential contributions of cyanobacteria to the formation of stromatolite and microbialite structures. Additionally, adaptations of cyanobacteria and their associated communities to permanently low temperatures were investigated. The community structures of two Antarctic lakes, Lake Joyce and Lake Untersee, were explored through the use of 16S and 18S rRNA gene amplicon sequencing. In Lake Joyce, distinct communities were observed between planktonic and benthic environments, confirming distinct ecological niches in the lake. In Lake Untersee, cone and pinnacle shaped structures were composed of different bacterial communities, highlighting a role of cyanobacterial behaviours in the mediation of structure morphology. Metagenomic analyses of Lake Untersee revealed a partitioning of nutrient cycling between upper and lower layers of the mats, with an increased functional potential for nitrification in the lower layers. Additionally, several coldinducible proteins, including cold-shock proteins and ice-binding proteins, and genes involved in nutrient-scavenging were identified in the communities implying that the mats are well-suited to the extreme polar habitat in which they reside. Finally, twelve novel cyanobacterial genomes were sequenced, unveiling potential genome-wide cold temperature related amino acid patterns as well as general mechanisms of stress-response and photoprotection. The work carried-out in this thesis significantly expands our knowledge of the unique benthic microbial mats of Antarctic perennially ice-covered lakes in the context of diversity, ecosystem function, and survival in extreme environments.

Date of Award	6 Dec 2022
Original language	English
Awarding Institution	University of Bristol
Supervisor	Marian Yallop (Supervisor), Gary L A Barker (Supervisor) & Anne Jungblut (Supervisor)