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We describe considerations and strategies for developing a nuclear magnetic resonance (NMR) sample preparation method to extract low molecular weight metabolites from high‐salt spent media in a model coculture system of phytoplankton and marine bacteria. Phytoplankton perform half the carbon fixation and oxygen generation on Earth. A substantial fraction of fixed carbon becomes part of a metabolite pool of small molecules known as dissolved organic matter (DOM), which are taken up by marine bacteria proximate to phytoplankton. There is an urgent need to elucidate these metabolic exchanges due to widespread anthropogenic transformations on the chemical, phenotypic, and species composition of seawater. These changes are increasing water temperature and the amount of CO2absorbed by the ocean at energetic costs to marine microorganisms. Little is known about the metabolite‐mediated, structured interactions occurring between phytoplankton and associated marine bacteria, in part because of challenges in studying high‐salt solutions on various analytical platforms. NMR analysis is problematic due to the high‐salt content of both natural seawater and culture media for marine microbes. High‐salt concentration degrades the performance of the radio frequency coil, reduces the efficiency of some pulse sequences, limits signal‐to‐noise, and prolongs experimental time. The method described herein can reproducibly extract low molecular weight DOM from small‐volume, high‐salt cultures. It is a promising tool for elucidating metabolic flux between marine microorganisms and facilitates genetic screens of mutant microorganisms.
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Biogeochemistry of Earth before exoenzymes
Microorganisms that transform and oxidize organic material (that is, heterotrophs) play a fundamental role in the geochemical cycling of key elements in the ocean. Through their growth and activity, heterotrophic microorganisms degrade much of the organic matter produced by phytoplankton in the surface ocean, leading to the regeneration and redistribution of nutrients and carbon back into the water column. However, most organic matter is physically too large to be taken up directly by heterotrophic microorganisms. Consequently, many heterotrophs secrete exoenzymes that break down large molecules outside the cell into smaller substrates that can then be directly taken up by the cell. The complex nature of the biochemical systems that microorganisms use to secrete these enzymes suggests that they were unlikely to have been present in the earliest heterotrophs. In a pre-exoenzyme ocean, heterotrophic microorganisms would only be able to access a small fraction of organic matter such that most dead phytoplankton biomass would have passed directly through the water column and settled onto the seafloor. Here we synthesize existing geobiological evidence to examine the fate of organic matter in the absence of exoenzymes in early oceans. We propose that on an Earth before exoenzymes, organic matter preservation, metal availability and phosphorus recycling would have operated differently than they do on the contemporary Earth.
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- Award ID(s):
- 2145434
- PAR ID:
- 10492131
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Nature Geoscience
- Volume:
- 16
- Issue:
- 10
- ISSN:
- 1752-0894
- Page Range / eLocation ID:
- 845 to 850
- Subject(s) / Keyword(s):
- early earth, biogeochemistry
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1038/s41561-023-01266-4
