H-Aquil: a chemically defined cell culture medium for trace metal studies in Vibrios and other marine heterotrophic bacteria
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A variety of trace metals, including prominently iron (Fe) are necessary for marine microorganisms. Chemically defined medium recipes have been used for several decades to study phytoplankton, but similar methods have not been adopted as widely in studies of marine heterotrophic bacteria. Medium recipes for these organisms frequently include tryptone, casamino acids, as well as yeast and animal extracts. These components introduce unknown concentrations of trace elements and organic compounds, complicating metal speciation. Minimal medium recipes utilizing known carbon and nitrogen sources do exist but often have high background trace metal concentrations. Here we present H-Aquil, a version of the phytoplankton medium Aquil adapted for marine heterotrophic bacteria. This medium consists of artificial seawater supplemented with a carbon source, phosphate, amino acids, and vitamins. As in Aquil, trace metals are controlled using the synthetic chelator EDTA. We also address concerns of EDTA toxicity, showing that concentrations up to 100 µM EDTA do not lead to growth defects in the copiotrophic bacterium Vibrio harveyi or the oligotrophic bacterium Candidatus Pelagibacter ubique HTCC1062, a member of the SAR11 clade. H-Aquil is used successfully to culture species of Vibrio, Phaeobacter, and Silicibacter, as well as several environmental isolates. We report a substantial decrease in growth rate between cultures grown with or without added Fe, making the medium suitable for conducting Fe-limitation studies in a variety of marine heterotrophic bacteria.
KeywordsVibrio Iron Marine heterotrophic bacteria EDTA Defined medium SAR11
This work was funded by the National Science Foundation (OCE 1657639 Granted to F.M.M.), the Princeton Environmental Institute (Grand Challenges to F.M.M. and Mary and Randall Hack Water Quality Award to D.L.M.), and the Princeton University Department of Geosciences (Undergraduate research funding support awarded to D.E.M.). We thank the Dyhrman lab (Columbia U.), Giovannoni lab (Oregon State U.), Bassler lab (Princeton U.) and Seyedsayamdost lab (Princeton U.) for providing bacterial cultures. We are especially grateful to K. R. Frischkorn for assistance with Trichodesmium epibionts, J. S. Valastyan for assistance with V. harveyi and S. Noell for assistance with SAR11.
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