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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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Elevated p CO 2 alters marine heterotrophic bacterial community composition and metabolic potential in response to a pulse of phytoplankton organic matter
Summary Factors that affect the respiration of organic carbon by marine bacteria can alter the extent to which the oceans act as a sink of atmospheric carbon dioxide. We designed seawater dilution experiments to assess the effect ofpCO2enrichment on heterotrophic bacterial community composition and metabolic potential in response to a pulse of phytoplankton‐derived organic carbon. Experiments included treatments of elevated (1000 p.p.m.) and low (250 p.p.m.)pCO2amended with 10 μmol L−1dissolved organic carbon fromEmiliana huxleyilysates, and were conducted using surface‐seawater collected from the South Pacific Subtropical Gyre. To assess differences in community composition and metabolic potential, shotgun metagenomic libraries were sequenced from low and elevatedpCO2treatments collected at the start of the experiment and following exponential growth. Our results indicate bacterial communities changed markedly in response to the organic matter pulse over time and were significantly affected bypCO2enrichment. ElevatedpCO2also had disproportionate effects on the abundance of sequences related to proton pumps, carbohydrate metabolism, modifications of the phospholipid bilayer, resistance to toxic compounds and conjugative transfer. These results contribute to a growing understanding of the effects of elevatedpCO2on bacteria‐mediated carbon cycling during phytoplankton bloom conditions in the marine environment.
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- Award ID(s):
- 1637396
- PAR ID:
- 10462664
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Environmental Microbiology
- Volume:
- 21
- Issue:
- 2
- ISSN:
- 1462-2912
- Format(s):
- Medium: X Size: p. 541-556
- Size(s):
- p. 541-556
- Sponsoring Org:
- National Science Foundation
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