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Insights Into Vitamin B12 Production, Use, and Acquisition by Marine Microbes

Erin Bertrand, Ph.D., 2012
Mak Saito, Advisor

Understanding factors controlling the distribution and magnitude of marine primary production is important for constraining global carbon cycling and elucidating selective pressures in marine ecosystems.  Although the potential for vitamin B12 availability to impact marine primary production has long been recognized, a lack of molecular-level tools has limited inquiry into the role of this cobalt-containing micronutrient in marine systems. This thesis describes the development of such tools and implements them to study B12 dynamics in the Ross Sea of the Southern Ocean.  Nucleic acid probes for B12 biosynthesis genes were designed and used to identify a group of B12 producers in this region. Bioassay experiments were used to show that iron availability may impact both B12production and consumption in natural communities. Lab-based studies profiled changes in diatom proteomes induced by low B12 availability and identified protein CBA1, a novel B12 acquisition protein in eukaryotic phytoplankton. Quantitative triple quadrupole mass spectrometry methods were developed to measure peptides from B12-related proteins in diatom cultures and field communities from McMurdo Sound in the Ross Sea, revealing that there is both B12 utilization and starvation in natural diatom communities and that direct peptide measurements hold promise as new tools in marine biogeochemistry.