Foraging at microscale

Current theory assumes that, while evolution has “optimized” microbes via natural selection, diverse species coexist because of trade-offs in their foraging, nutrient uptake, and metabolic strategies. To better understand the structure and dynamics of microbial ecosystems, we must therefore relate microbial behaviors to growth rates in their natural environments. Specifically, we study how microscale nutrient heterogeneity determines the success of different foraging strategies, and ultimately impacts macroscale biogeochemical cycles in the ocean. We use concepts from optimal foraging theory to model the foraging behaviors and growth rates of microbes, allied with microfluidic experiments implementing different nutrient landscapes. We are currently working to understand the benefits and costs of copiotrophic strategies, such as motility, metabolic specialization, and surface attachment. For example, our previous experimental work showed that motility increases nutrient uptake from lysing diatoms, and that different strains of a marine microbe coexist by differentially attaching to nutrient particles based on a competition-dispersal trade-off. To gain insight into the swimming strategies of marine bacteria, we used stochastic stability theory to mathematically model them and explore differences in their performance in responding to chemical gradients. Now we are adapting tools from robotics to develop molecular-level resource allocation models that allow us to quantify the proteomic, energetic, and genomic costs of microbial behaviors from first principles. For more information, please contact Francesco Carrara (carraraf@ethz.ch) or Noele Norris (norris@ifu.baug.ethz.ch).