Research Topics

Phytoplankton physiological ecology, Biocomplexity and microbial diversity, Planktonic ecosystem processes in marine estuarine and freshwater systems

The long-term goal of my research program is to improve our understanding of phytoplankton physiological ecology, population dynamics, community structure, and ecosystem roles by taking an autecological approach to investigating the lives of these microorganisms. The tools we use to answer these questions include observational and experimental (e.g., dilution gradient and nutrient addition) field studies, which are analyzed by techniques such as flow cytometry; lab-based investigations of phytoplankton physiology using various isolates growing in culture; and a variety of molecular biological, molecular genetic, and biochemical techniques. For many reasons, the cyanobacteria are the predominant model system used in my lab.

One part of my lab is focused on investigating basic cyanobacterial molecular genetics and physiology. For example, with support from DOE we are investigating the function of a thioredoxin-like gene, TxlA, which is found only in cyanobacteria and photosynthetic eukaryotes. Also with support from DOE and in collaboration with Chip Lawrence and coworkers at Wadsworth, we are just embarking on a new project that will take advantage of the availability of several complete cyanobacterial genome sequences to define the transcription regulation networks in cyanobacteria.

Another major focus of work in my lab grew out of my interest in the utilization of urea as a nitrogen source by marine Synechococcus. As part of an NSF-funded Biocomplexity project (http://geoweb.princeton.edu/research/biocomplexity/index.html), we are investigating the biochemically-defined functional group of microorganisms that can degrade urea, which is one of many potentially important but poorly understood forms of organic nitrogen present in aquatic ecosystems. Since most organisms use the well-conserved enzyme urease to degrade urea, we have designed oligonucleotide primers that are expected to be universal; that is, they should enable us to amplify any urease gene. Application of these primers to samples from Chesapeake Bay has revealed a very high diversity of urease sequences. Our current efforts are focused on developing a similar approach to describe the diversity of phytoplankton, and to adapt both to high-throughput technologies, such as gene array hybridization.

A third part of my lab is focused on investigating the comparative ecology of the small (<2 mm) planktonic picocyanobacteria that are found in both marine and freshwater ecosystems. We have been using flow cytometry and molecular techniques to investigate the picocyanobacteria in Lake George, NY, which we have found to be numerically dominated by organisms very much like marine Synechococcus. A similar project, funded by the Hudson River Foundation, is underway in the Hudson River Estuary, where we are seeking to define the role of picophytoplankton in the estuarine food web.