Simulating Dead-End State Distributions for Microbial Metabolism

Session: (In-Person) Poster Presentation

In this project, I simulate the influence of microbial metabolism on ocean geochemistry using the Cariaco Basin, Venezuela as a model system. In my investigation, I used bifurcation diagrams to visualize the distribution of possible dead-end states: geochemical configurations at which all metabolic reactions become energetically unfavorable and microbial metabolism slows to a halt. In a radically novel approach, I used an Ornstein-Uhlenbeck process to stochastically model kinetic rates.

My rationale for doing this was to show how stoichiometry and energetics alone could potentially determine long-term biogeochemical states. By running N=9,336 simulations written in Python, I found that the dead-end state of an isolated system with aerobic sulfide-oxidizing microbes could be determined fairly consistently based on varying oxygen levels. At high oxygen concentrations (>100 micromolars), oxygen was utilized to the fullest metabolic extent (until the Gibbs free energy yield reached 0 kJ / mol) by the simulated microbes in order to convert all available sulfide to sulfate.

At lower oxygen levels, nitrate was utilized instead due to its biochemical role as an alternative electron acceptor. At higher oxygen levels, final nitrate concentrations were far less predictable, and significant variation in nitrate consumption can be seen in the associated bifurcation plot. This theoretical exercise may aid in the development of biogeochemical models of climate-influenced ocean processes.