| Summary: | Marine microorganisms harbour the potential to either amplify or attenuate global warming through their ability the control the ocean-atmosphere flux of climatically important gases, such as carbon dioxide. The aims of this study were to investigate both community and individual level responses of marine microorganisms in response to rising CO2 levels. Chapter one reports the effects of elevated CO2 on biofilm formation across a naturally occurring pH gradient. Biofilm biomass increased in both light communities dominated by bacteria and highlight communities dominated by microalgae. The microalgae showed a significant increase along the pH gradient and a community shift was present at each site along the gradient. The increase in biomass will help support coastal ecosystems in which maintenance and reproduction at lower pH increases the energetic requirement of marine benthos. Chapter two aimed to identify key baseline physiological functions of model bacterial representatives from an ecologically significant clade to gain a greater understanding of their role in biogeochemical cycling. Octadecabacter arcticus 238, a polar bacterium, displayed light stimulated growth due to the presence of a putative light-driven proton pump, but did not increase its bacterial growth efficiency. A number of representatives from the Marine Roseobacter Clade harbouring genes for inorganic sulfur oxidation were screened for their ability to utilize thiosulfate as an auxiliary energy source. Across six different strains, a variable response from inhibition to enhanced growth was observed. Ruegeria pomeroyi DSS-3 was severely inhibited when grown on agar plates but showed a completely opposite response when grown in a planktonic state of living. In the planktonic state, R. pomeroyi DSS-3 appeared to assimilate more carbon into biomass which was evident through an increase in final cell yields. The different physiological roles for sulfur oxidation between these strains illustrate the importance of physiological experimentation to supplement genomic investigation. The different outcomes of supplementary energy generation in two divergent strains of bacteria could have fundamentally opposite implications for carbon cycling within marine surface waters. Faculty of Science
|
|---|