The goal of our research is to learn how cells communicate with their environment and how that information is used to control gene expression and enhance survival. We are specifically interested in a ubiquitous group of marine heterotrophic bacteria, members of the Roseobacter clade, and their interactions with other bacteria and eukaryotes in the ocean. Our Roseobacter research projects cover five areas: (1) genomics, (2) motility and chemotaxis, (3) biofilm formation, (4) production of antibiotics, and (5) coral bleaching and ocean health.

Some roseobacters, like Silicibacter sp. TM1040 (our model roseobacter), form symbioses with phytoplankton many of which are associated with harmful algal blooms (HABs). Bacteria may affect phytoplankton physiology in many ways, including the production of growth-modifying metabolites, the synthesis, modification, or breakdown of algal toxins and precursors, and through interactions that modify eukaryotic behavior. The goal of our research is to elucidate the molecular mechanisms used by the bacteria in this symbiosis.

Through a combination of genomics, bioinformatics, molecular biology, microbiology, and microbial genetics we have ascertained that Silicibacter sp. TM1040 uses a variety of mechanisms to initiate and maintain its symbiosis with phytoplankton. For example, TM1040 uses chemotactic signaling and flagellar motility to sense dimethylsulfoniopropionate (DMSP) and amino acids produced by the phytoplankton. The bacteria respond by moving towards the phytoplankton. Once near the surface of the eukaryote, other (unknown) stimuli trigger a change in the bacteria that allows them to attach to the cell surface of the alga and form a biofilm. During the process of biofilm formation, the physiology of the cells changes. One of these changes that occurs in the biofilm is the production of an antibiotic, tropodithietic acid. Tropodithietic acid (TDA) may serve multiple functions during this symbiosis, e.g., it likely prevents other bacteria that may harm the phytoplankton from occupying the niche on the surface of the alga. TDA also may be involved in maintaining the health of coral reefs and in aspects of global climate control, topics that we are actively pursuing.