Protein regulation in Trichodesmium and other marine bacteria: Observational and interpretive biomarkers of biogeochemical processes

Noelle Held, Ph.D., 2019
Mak Saito, Advisor
Marine microbes play key roles in global biogeochemistry by mediating chemical transformations and linking nutrient cycles to one another. Molecular biomarkers are important tools in chemical oceanography because they allow microbial behavior to be both observed and interpreted. In this thesis, I develop a holistic approach to the study of marine microbes. I begin by identifying unique patterns in the sensory systems of marine bacteria and suggest that these represent an adaptation to the marine environment. Building from this, I focus on the diazotroph Trichodesmium, whose activity affects multiple biogeochemical cycles. Metaproteomes of field Trichodesmium populations indicated that iron and phosphate co-stress is the norm rather than the exception owing to the biophysical limits of membrane space and diffusion. I next investigated metaproteomes of individual Trichodesmium colonies captured from a single site, demonstrating variability in iron acquisition including from minerals. Next, I investigated diel proteomes of Trichodesmium erythraeum IMS101 to understand how and why nitrogen fixation occurs in the day. This thesis develops a fundamental understanding of how Trichodesmium and other organisms affect, and are affected by, their surroundings. Future work can focus on benchmarking protein biomarkers and continued connection of systems biology frameworks to the study of ocean chemistry.