Microbial decision-making and the link to ocean biogeochemical cycles

Marine microbes play critical roles in global biogeochemistry by mediating chemical transformations and linking elemental cycles to one another. As the molecular machines that drive biogeochemical transformations, microbial proteins reveal aspects of both a microbe’s internal state and its external environment. Protein biomarkers, similar to those used in paleo-oceanography but now applied to the modern ocean, can be used to “diagnose,” for example, nutrient limitation of microbial growth, the rates of reactions such as nitrogen fixation, and the chemical speciation of nutritive elements. Biological complexity such as biochemical regulatory networks, biophysical constraints, and microbial individuality can complicate the interpretation of protein biomarkers, but can also be leveraged to understand new aspects of life-environment interactions.  In this seminar, I will take as a case study the nitrogen fixing marine cyanobacterium Trichodesmium, which provides up to 80Tg of fixed nitrogen to the surface ocean annually. Through protein biomarkers, computational modelling, and nutrient chemistry I describe the intricate inner workings of this keystone marine microbe and reveal new aspects of its role as an integrator of the carbon, nitrogen, phosphorus, and iron cycles. Specifically I will demonstrate that the biogeochemical niche of Trichodesmium can be understood only through a holistic, systems-level lens. This example sets the stage to build global biogeochemical understandings from the ground up, beginning from the biochemistry of individual marine microbial cells.