We cannot observe microbes eating in their natural environment, so figuring out how microorganisms in the ocean get their food and energy is one of the largest challenges in marine microbiology. The diet of these microbes ultimately controls how materials like carbon cycle through the ocean. While the smallest microbes can take up their nutrients directly from the surrounding seawater, larger microbial cells may rely on a variety of strategies, often switching between different ways of acquiring food and energy. They may switch from plant-like modes of growth (using sunlight for energy) and animal-like modes of growth (eating other microbes). They may also be reliant on partnerships with other microbes that provide them with essential nutrients. Our project will investigate “who is eating who” in the ocean, and whether some microbes have eluded cultivation because of their unique lifestyles.
Ecological interactions determine community composition and therefore the flow of carbon and nutrients through ecosystems. Like some prokaryotic taxa, specific microbial eukaryotic taxa may act as keystone species determining community assembly through primary production, grazing, symbiosis, parasitism and recycling of biological material. Although photosynthetic eukaryotes have been studied intensively, heterotrophic and mixotrophic eukaryotes are among the most poorly studied marine microbes. This project addresses the complex interactions among microbial eukaryotes and interactions with other domains of life by investigating model trophic interactions in the central California Current system. The study region encompasses a gradient from highly productive coastal waters to the oligotrophic gyre. We are combining field experiments, metagenomic sequencing, single cell sorting, and stable isotope tracers to unravel these complex trophic interactions. New efforts at cultivating uncultivated microbial eukaryotes will help bring more species into culture to act as model systems for these understudied nutritional modes.