| Summary: | Thesis (PhD (Genetics))--University of Pretoria, 2022. Understanding the ecological patterns of microbiota in natural ecosystems is fundamental for predicting their responses to global change. As mediators of biogeochemical cycles, microbiota are essential for ecosystem functioning in the oceans. Estimates suggest that nearly half of the Earth’s net primary productivity occurs in the oceans. Yet surprisingly, the oceans are the least studied ecosystems. Physical oceanographic studies have shown that the Southern Ocean (SO) is a crucial marine carbon and heat storage. This research supports the solubility pump as the main driver of oceanographic processes in the SO. Recent studies on phytoplankton have shown the centrality of biological processes, but comparatively less is known regarding the role played by microorganisms. In this study, we performed a comprehensive analysis of the structure and function of SO microbial communities. We assessed microbiota from the epipelagic to the bathy- and abyssopelagic zones of the ocean, revealing remarkable insights regarding microbial community dynamics. The applications of several culture-independent techniques allowed us to substantially reduce the knowledge deficit regarding SO microbiomes and the effect of nutrient variables on their diversity and structure. The effect of an early spring phytoplankton bloom on the abundance, diversity, and structure of prokaryotes was assessed. Our results showed that an early spring bloom had limited effects on microbiota but increased total prokaryotic abundances in epipelagic waters. We also observed some compositional changes including an increase of Cyanobacteria. However, diversity and community structure remained consistent. Specific physicochemical parameters factors appear to drive microbial communities , including the availability of various nutrients and oceanographic variables determining SO water masses. Shotgun metagenomic sequencing allowed us to provide a compendium dataset of 628 metagenome-assembled genomes. Of ...
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