CAREER: Determining microbial metabolisms that transform primary production and mediate biogeochemical cycling on coral reefs

Microbes are master manipulators of metabolites in the sea, promoting nutrient recycling through mineralization of organic matter, and transformation of organic matter via enzymatic activity. Reef-associated microbes play key roles in nitrogen fixation, nitrification, transformation of dimethylsulfoniopropionate into amino and nucleic acids, iron scavenging, and synthesis of B vitamins, contributing widely to the exchange of mineral nutrients and cofactors essential for reef fauna.

Prior research has illustrated consistent enrichment of distinct microbial populations on coral reefs relative to the ocean, a pattern demonstrated across the globe. The abundances of these taxa fluctuate diurnally suggesting their metabolism is linked to biophysical factors such as light, resource availability or oxygen concentrations. This project seeks to understand how coral reef-derived organic substrates select for distinct microbial taxa and determine how the metabolism of these core reef microbes influences ecological processes.

Understanding how organisms interact to exchange metabolites or signal a physiochemical event is also essential to successfully mitigate complex environments for restoration or resource management. Ongoing macroalgal phase shifts on coral reefs are hypothesized to be a consequence of coastal pollution, and this project will directly inform knowledge about how these changes are impacting microbial populations and their metabolism on the reefs of Moorea.

This project includes the development of a 4-week undergraduate research experience and field course centered around marine microbiology and biogeochemistry at Gump Station in Moorea, followed by sustained mentorship until graduation through engagement with the SIO community.

Coral reef microbes facilitate the exchange of metabolites among different community members through chemical transformations as part of their diverse metabolic repertoire. The proposed study will test the overarching hypothesis that nutrient-rich organic matter released into the seawater environment by benthic primary producers selects for specific microbial taxa which in turn facilitate central ecosystem processes, such as nutrient retention, calcification, homeostasis, and maintenance of biodiversity.

This research will be accomplished through three main objectives that combine molecular approaches (genomics and metabolomics) with biogeochemical measurements and evaluates these parameters across scales, from mesocosm experiments to in situ reef habitats. The first campaign will construct high-quality metagenomic assembled genomes (MAGs) of core microbial taxa consistently enriched in coral reef environments.

These genomes will be used to inform a second experimental campaign that measures the metabolic gene expression of core microbial populations in a controlled mesocosm setting. Third, in situ samples will be used to compare gene expression of core microbial populations collected across established spatial gradients of benthic cover and nutrient availability, providing a robust context to determine the differences in microbial metabolism between coral- and algal-dominated reef habitats.

This project will be conducted within the Moorea Coral Reef Long Term Ecological Research program, leveraging a wealth of time series data on multiple reef habitats.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.