overview: marine microbes & carbon flux
Each year, unicellular algae (aka, phytoplankton) in the oceans generate nearly as much organic carbon as plants on land. About half of this phytoplankton-derived carbon (~20 Gt C) is degraded by heterotrophic bacteria within minutes to weeks, through a process referred to as the microbial loop. This trophic transfer between phytoplankton and bacteria accounts for the largest flux of carbon through the ocean and regulates the balance between remineralization to CO2 and carbon storage in the deep ocean. We are interested in understanding the metabolic relationships between the microorganisms and substrates that mediate this large flux of energy and matter.
Diatoms under microscope.
model systems approaches to study marine microbe-microbe interactions in the lab
To explore metabolite exchange in phytoplankton-bacterial interactions, we employ model microbial system approaches where marine phytoplankton and bacteria are co-cultured together in the lab. Then, gene expression (transcriptomics) and chemical analyses (metabolomics) are used to assay for compounds passed between the two organisms. Through these approaches, we have detected exchange of novel organosulfur molecules (sulfonates) between diatoms and bacteria. Genes for biosynthesis and degradation of sulfonates have limited distribution among phytoplankton and bacteria, respectively, suggesting that sulfonated substrates underlie targeted microbial interactions.
In a two-member model system between the diatom T. pseudonana and the bacterium R. pomeroyi, transcript and metabolite patterns reveal exchange of the diatom-derived sulfonate DHPS (dihydroxypropane sulfonate).
field-based ‘omics measurements to decipher microbial community activity
We also use field-based observations to track how organic metabolites are cycled in natural plankton populations. By combining environmental measurements of cellular metabolite and transcript abundances, we can “watch” metabolite cycling by simultaneously tracking compound abundances inside plankton cells along with gene expression in the phytoplankton and bacterial taxa that synthesize and catabolize them, respectively. This integrative approach allows us to better understand how microbial interactions and metabolite exchange contribute to marine carbon flux and ecosystem interdependencies.
Collection of plankton samples onboard the Research Vessel Thomas G. Thompson; Photo credit: Robyn Von Swank.
organic sulfur metabolisms
We are broadly interested in understanding the flow or organic sulfur between marine phytoplankton and bacteria. While our model systems approaches implicate sulfonates in phytoplankton-bacteria interactions, the production of sulfonates, as well as other organic sulfur compounds, is critical to phytoplankton physiology. Using combined laboratory and field observations, we are interested in defining the organic sulfur pool, identifying metabolic pathways of organic sulfur metabolism in marine microbes, and quantifying the contribution of organic sulfur to marine carbon and energy flux.
Some of the sulfonates identified in marine plankton samples that are implicated in microbial interactions.
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