The Influence of Changing Temperatures on Cyanobacterial Oxic Methanogenesis

Abstract

Methanogenesis has long been considered to be a strictly anaerobic process, but in recent years researchers have proposed that it can occur in oxic environments from oxygen phototrophs such as cyanobacteria. Methane is a greenhouse gas that is 28-34 times stronger than carbon dioxide and plays a large role in the ongoing climate crisis. Methane’s high potency stress the importance in understanding its sources in the hope of developing better mitigation and adaptation methods in the future. This thesis examines how the headspace concentration of methane, alongside carbon dioxide and nitrous oxide, vary between four cyanobacterial strains, in axenic and non-axenic cultures, at three different temperatures. Cyanobacterial growth curves were determined using optical density and headspace concentrations analysed with gas chromatography. Cyanobacteria were determined to both positively and negatively influence methane concentrations, but ambiguity still remains as to
whether these concentration changes can be attributed to oxic methanogenesis, interactions with the wider microbiome or from other processes such as organic matter decay or formation of microanoxic zones. Temperature was not found to have a statistically significant relationship (p < 0.05) with methane for any of the cyanobacterial cultures. But, it was concluded that higher temperatures typically resulted in more variability of methane concentration. The exact cause of these variations remained uncertain and highlighted areas of the research that are critical to explore further to fully understand oxic methanogenesis and its implications on the methane budget and climate change.

Date of Award	10 Dec 2024
Original language	English
Awarding Institution	University of Bristol
Supervisor	Patricia Sanchez-Baracaldo (Supervisor) & Joshua F Dean (Supervisor)