Growth and physiology of the green microalga, Coccomyxa subellipsoidea

: a comparison of an Antarctic and temperate strain and the influence of temperature and irradiance

Abstract

Coccomyxa is a genus of unicellular green algae with a cosmopolitan distribution. Species of this genus have been suggested to be physiologically plastic due to their diverse range of lifestyles. The genome of an Antarctic isolate of Coccomyxa subellipsoidea was the first polar green alga to be sequenced and it became a model organism for cold tolerance because it was revealed to possess a range of genes associated with survival at low temperature. It has been proposed that C. subellipsoidea may be a potential candidate for biofuel generation due to the large quantity and diversity of lipids synthesised. However, knowledge of the growth, physiology and biochemistry of this species is scarce. The aim of this thesis was to investigate these aspects of C. subellipsoidea and to determine if latitudinally-separated strains are physiologically distinct. The growth, photosynthetic activity, pigment composition and rate of respiration were measured for two strains: a strain isolated from algal peat in the Antarctic and a strain isolated from a lichen in a temperate region. Both were grown across a range of temperatures and irradiances. The Antarctic strain was tolerant of low temperature and demonstrated eurythermal behaviour with remarkably consistent levels of growth, photosynthetic activity and respiration between 6 and 18 °C. However, the temperate strain was much more sensitive to temperature, with a significant impairment of growth and photosynthetic activity at 6 °C. The Antarctic strain may be relatively resilient to climate change, whereas the temperate strain could be more sensitive to climate change. These findings suggest that C. subellipsoidea is a plastic species which may be segregated into physiologically distinct populations, each uniquely adapted to their latitude of origin. The cold tolerance genes previously identified in the genome of the Antarctic strain may not be present or expressed to same extent in temperate strain. Future studies could employ molecular techniques to compare gene expression levels in these strains of C. subellipsoidea.

Date of Award	24 Mar 2020
Original language	English
Awarding Institution	The University of Bristol
Supervisor	Marian L Yallop (Supervisor)