Project: Models of Marine Microbial Biogeography and Biogeochemistry
Microbial communities in the sea mediate the global cycles of elements including climatically significant carbon, sulfur and nitrogen. Photosynthetic microbes in the surface ocean fix carbon and other elements into organic molecules, fueling food webs that sustain fisheries and most other life in the ocean. Sinking and subducted organic matter is remineralized and respired in the dark, sub-surface ocean maintaining a store of carbon about three times the size of the atmospheric inventory of CO2. The communities of microbes that sustain these global-scale cycles are functionally and genetically extremely diverse, non-uniformly distributed and sparsely sampled. Their biogeography reflects selection according to the relative fitness of myriad combinations of traits that govern interactions with the environment and other organisms. Trait-based theory and simulations provide tools with which to interpret biogeography and microbial mediation of biogeochemical cycles. Several outstanding challenges remain: observations to constrain the biogeography of marine microbes are still sparse and based on eclectic sampling methods, theories of the organization of the system have not been quantitatively tested, and the models used to simulate the system still lack sufficiently mechanistic biological foundations that will enable meaningful, dynamic simulations and state estimation.
We propose: to integrate key new data sets in real time as they are collected at sea to facilitate direct tests of theoretical predictions; to synthesize an atlas of marine microbial biogeography suitable for testing some specific ecological theories and quantifying the skill of numerical simulations; to develop new trait-based models and simulations of regional and global microbial communities bringing to bear the power of metabolic constraints and knowledge of macro-molecular composition; to analyze these data and models using statistical tools to interpolate and extrapolate the sparse data sets, formally quantify the skill of numerical simulations, and employ data assimilation technologies to identify and optimize compatible model frameworks. Together, the results of these efforts will advance new theoretical approaches and lead to improved global ocean-scale predictions and regional state-estimates, constrained by observed biogeography. They will provide a quantification of the associated biogeochemical fluxes.
Project: Interpreting the organization of microbial communities in the North Pacific using theory and numerical simulations.
Natural microbial populations can appear bewilderingly complex, with assemblages of organisms spanning many orders of magnitude in size, diverse biochemical functionality, and extremely rich genetic variation. In any system we seek to understand which actors are present, which are absent, and why? What are the consequences for the ecosystem function and the flow of elements in that environment? Idealized theory and numerical simulations provide a means to synthesize and organize understanding of the pressures that shape microbial systems. They help frame hypotheses that can be tested in the laboratory and field.
In this collaborative effort we will employ data, theory and numerical simulations to test the hypothesis that the large-scale horizontal and vertical structures of the microbial communities of North Pacific Subtropical Gyre reflect a system close to equilibrium, organized by resource supply ratios. We will develop new, quantitative descriptions of the costs and benefits to the individual of specific functionality, including nitrogen fixation, and of both competition and cooperation between diverse microbes. Basin-scale numerical simulations the circulation, chemistry and ecosystem of the North Pacific will provide a means to illustrate and explore the large-scale consequences of these small-scale interactions.
Mick Follows is a professor of oceanography in the Department of Earth, Atmospheric and Planetary Sciences at MIT. He seeks to understand how the interactions of physical, chemical and biological processes modulate the structure and function of marine microbial communities and regulate elemental cycles on the global. To this end he develops and employs idealized theory, numerical simulations, and analysis of observed data. Over the past decade, he has become increasingly fascinated by the biological and ecological aspects of global elemental cycles and developed a new platform for simulating and interpreting the structure, function and biodiversity of marine microbial populations. The approach relies upon the self-assembly of communities from a diverse pool of virtual phenotypes. It provides a bridge between clean concepts from theoretical ecology and the typically sparse observational data from marine ecosystems. To date, this work has focused on marine phytoplankton populations. Currently, Follows and his group are extending the approach to provide more general description of marine microbes including a broader set of trophic strategies. To understand the ecological sorting of populations, we seek to quantitatively understand and model the costs and benefits of particular organismal traits and interactions, constrained by conservation of mass, electron and energy flow. Follows is a Fellow of the American Academy of Microbiology.