Stilianos Louca, Ph.D.

California Institute of Technology

Project: Multi-layered biogeochemical models, from genes to microbial communities

Microorganisms are the most ancient and the most diverse life-form on Earth. Through their metabolic activity, millions of different microorganisms are driving global biochemical fluxes and have been shaping the ocean’s chemistry for billions of years. Yet, we understand very little about how microbial metabolism affects marine biogeochemistry, partly because the enormous diversity of microbial communities makes it hard to model them mathematically. Despite the millions of extant microbial species, most global elemental fluxes are driven by a core set of genes for energy transduction, each found within multiple microbial clades. It is conceivable that the dynamics of these genes at ecosystem scales may, to a certain approximation, be modeled independently of the taxa hosting each gene. A gene-centric description of microbial metabolic networks, if accurate, would greatly simplify the modeling of marine ecosystems. The precise distribution of genes across genomes, and co-occurrences of genes with traits not directly related to energy transduction, such as susceptibility to viruses, may constitute “higher order” corrections to gene-centric models. The importance of such corrections is currently unknown. Understanding how genes and genomes interact with their environment to drive biochemical fluxes, is needed for constructing accurate models of the ocean. I will use sediment and biofilm microcosms to investigate the effects of geochemical conditions and microbial community structure on microbial metabolism. I will use DNA sequencing, isotope labeling techniques and substrate enrichments to investigate how the microcosms respond to stimuli. This will give insight into the dynamics of the microbial metabolic networks and allow comparison of these dynamics to various aspects of microbial community structure.

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