| Summary: | Cobalamin has the potential to limit primary productivity and shape the structure and ecological interactions of marine microbial communities. The identification of major sources and sinks of this vitamin is needed in order to understand its availability in the ocean. In this thesis, assembly-based and short-read-based approaches were combined to analyze metagenomic samples from the Scotian Shelf and Slope region of the Northwest Atlantic. This resulted in the first identification of major producers, remodelers and consumers of cobalamin and related compounds in this region. Mass-spectrometry tools to monitor the contribution of Synechococcus, an important cyanobacterial group, to the cobalamin cycle in the Northwest Atlantic were also identified. The implementation of these tools in culture experiments enabled the identification of environmental and physiological factors with potential to affect cyanobacterial contributions to cobalamin cycling in this region. In sum, this thesis is a step towards elucidating the influence that cobalamin may have on marine primary productivity and microbial ecological interactions in the Northwest Atlantic.
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