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Alphaproteobacteria facilitate Trichodesmium community trimethylamine utilization
Asa E Conover1, Michael Morando1, Yiming Zhao1
1Department of Marine and Environmental Biology, University of Southern California, CA, USA.
Environmental Microbiology
|September 14, 2021
Summary
Marine microbes help Trichodesmium, a nitrogen-fixing cyanobacterium, utilize trimethylamine (TMA) as an alternative nitrogen source. Roseobacter bacteria metabolize TMA, providing nitrogen to Trichodesmium and influencing ocean nutrient cycling.
Area of Science:
- Marine microbiology
- Biogeochemical cycles
- Cyanobacteria physiology
Background:
- Trichodesmium, a nitrogen-fixing cyanobacterium, forms nutrient-rich oases in oligotrophic oceans, supporting primary productivity.
- Associated microbes can influence Trichodesmium physiology, potentially aiding its growth.
- Trimethylamine (TMA) inhibits Trichodesmium nitrogen fixation but not growth, suggesting it as an alternative nitrogen source.
Purpose of the Study:
- To investigate the metabolism of trimethylamine (TMA) by Trichodesmium and its associated microbial community.
- To determine if TMA-nitrogen is directly assimilated or cross-fed by microbial associates.
- To identify the specific microbes involved in TMA metabolism.
Main Methods:
- Stable isotope probing (SIP) using 15N-labeled TMA on Trichodesmium enrichments.
- Genomic analysis to identify TMA-metabolizing bacteria and their metabolic pathways.
Main Results:
- Two members of the marine Roseobacter clade (MRC) of Alphaproteobacteria were identified as key TMA metabolizers.
- Genomic data indicate these MRC bacteria convert TMA into ammonium (NH4+).
- This ammonium is then utilized by Trichodesmium and the broader microbial community.
Conclusions:
- Microbiome-mediated transformations of carbon and nitrogen influence Trichodesmium nitrogen fixation.
- Host-associated heterotrophs play a crucial role in modulating nitrogen cycling in marine environments.
- This study highlights the ecological significance of microbial interactions in global biogeochemical processes.
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