Differential activity of coexisting cells
There are 100,000 Prochlorococcus cells in every milliliter of surface water across Earth's vast open oceans making these cells the most abundant photosynthetic cell on the planet. We know these cells are incredibly diverse. They form distinct clades based on light, temperature, and nutrient acquisition strategies and exhibit extensive diversity in the leaves of the trees even between single cells. One major unanswered question is: Do coexisting Prochlorococcus of distinct genetic lineages contribute equally to primary productivity in the microbial community? Through oceanographic field studies and laboratory work with cultivated isolates that represent wild Prochlorococcus communities our research group aims to understand how small differences in genome sequences allow these cells to contribute to nutrient and energy cycles on global scales in different ways. This work is funded by the NSF Biological Oceanography Program (NSF-OCE #1646709).
Microbes as prey
Picocyanobacteria population sizes are remarkably stable. Each day, cell division is balanced with mortality, to maintain large stable populations. Viruses are one known source of mortality. Likewise, single celled alga have been observed to consume cyanobacteria. Gathering evidence suggests that large gelatinous zooplankton may also be a significant source of mortality to microbes of the open ocean. However, the difficulty of studying these delicate gelatinous creatures, and their patchy distributions, leave much to be learned of their grazing rates and selectivity. We have teamed up with the Sutherland Lab at the University of Oregon to measure the grazing rates and selectivity of five understudied groups of pelagic tunicates (gelatinous grazers, e.g. pyrosomes, salps, etc.) coupling SCUBA-based sampling, videography, and microbiome techniques in open-ocean ecosystems. This project is funded through NSF-OCE (Award #1851412).
Physical oceanographic processes create complex patterns of light availability for marine picocyanobacteria. Phytoplankton of the surface ocean are kept in constant motion by physical processes in the surface mixed layer. Thus, cells have evolved to depend on an energy source (light) that varies on time scales from hours to days in predictable and sometimes unpredictable fashions. From static light availability in a stratified water column to periodic mixing below the euphotic zone, the range of different light regimes phytoplankton may experience is great. To measure the impact of variable light on picocyanobacterial growth we are recreating ocean mixing scenarios in the lab and "stress-testing" cells for their ability to withstand different mixing scenarios. In addition, we are linking photoacclimation state of natural picocyanobacterial assemblages to fine-scale measurements of physical processes in the Pacific Ocean.
Great Lake Picocyanobacteria
Picocyanobacteria form the base of the food web in the Great Lakes. As in marine environments, these Great Lake picocyanobacterial populations are genetically diverse and occupy a range of distinct environments across lakes and depths. Through NSF-OCE Award# 1830002 we are working with the Coleman Lab at the University of Chicago to connect picocyanobacterial genotypes and phenotypes in the Great Lakes towards better understanding of how these populations shift with environmental change. Specifically, we will be applying our 5-laser flow cytometry technique to distinguish coexisting Synechococcus populations based on their pigments.