The response of the cryoconite microbial community to cryospheric stresses

Abstract

The cryosphere covers a substantial proportion of our planet and although a harsh environment, is home to various, relatively understudied, microbial ecosystems. Cryoconite holes are one such ecosystem and form when a mixture of windblown microbial and mineral particles accumulate on a glacier surface, and due to the low albedo of the dark coloured granular aggregates, melt down into the ice. Cryoconite harbours rich, biodiverse microbial communities which experience numerous cryospheric stresses and extreme conditions. Previously, the majority of cryoconite biological studies examined community productivity during the summer or focused on the primary producer Cyanobacteria. Few studies examined the stress response and physiological abilities of the community or of individual taxa under differing cryospheric stressors, or indeed the genomic foundations of such responses. Here, the cryoconite community and individual isolates were subjected to two cryospheric stressors, light and temperature. Both 24-hour dark and 24-hour light conditions as well as temperatures above (+2 °C ) and below (-5 °C ) freezing were applied. The community demonstrated a rapid recovery following a diurnal freeze-thaw (a return to pre-freeze levels of net O2 production within 48 hours). Additionally, isolates were able to produce increasing CFU/ml -1 values following incubation over a period of weeks at -5 °C, indicating an ability to not only withstand and recover from sub-zero temperatures but potentially to multiply at such temperatures. Furthermore, UV exposure as a form of light stress was applied to a selected cold-adapted heterotrophic representative, isolate A18.2, and although non-significant at this stage, results indicate the pigment produced by the isolate may confer some protection against UV irradiation. Sequencing and assembly of metagenomes and genomes followed by annotation and surveying of shock, stress, coldadaption associated, light-sensing and carotenoid biosynthesis genes provided additional insight to the responses observed to the given cryospheric stresses. As well as genes previously associated with cold-adaption, the gene encoding gsp69 (yhdN) was identified as one of the core shock, stress or cold-adapted genes. yhdN was one of the most abundant stress genes and was present in every metagenome and genome, which indicates its potential, previously unknown link to cold-adaption. Moreover, the prevalence of light-sensing and carotenoid biosynthesis genes as well as the lightinduced increase in pigment production demonstrated in both the community and the A18.2 implies this response to light stress could be a common tactic in cryoconite communities. By uncovering these adaptive abilities and responses to light and temperature stress as well as gaining genomic insight into the basis of these abilities, understanding how members of the cryoconite community, and further, how microbes overcome life in the cryosphere, has been furthered

Date of Award	2020
Original language	English
Awarding Institution	Aberystwyth University
Supervisor	Arwyn Edwards (Supervisor) & Luis Mur (Supervisor)