Cellular content of biomolecules in sub-seafloor microbial communities

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    Stefan Braun, Yuki Morono, Geomicrobiology Group, Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, Nankoku, JapanKevin W. Becker, Organic Geochemistry Group, MARUM and Department of Geosciences, University of Bremen, GermanyKai-Uwe Hinrichs, MARUM, Bremen University, Germany
  • Kasper Urup Kjeldsen
  • Bo Barker Jørgensen
  • Bente Aagaard Lomstein
Microbial biomolecules, typically from the cell envelope, can provide crucial information about distribution, activity, and adaptations of sub-seafloor microbial communities. However, when cells die these molecules can be preserved in the sediment on timescales that are likely longer than the lifetime of their microbial sources. Here we provide for the first time measurements of the cellular content of biomolecules in sedimentary microbial cells. We separated intact cells from sediment matrices in samples from surficial, deeply buried, organic-rich, and organic-lean marine sediments by density centrifugation. Amino acids, amino sugars, muramic acid, and intact polar lipids were analyzed in both whole sediment and cell extract, and cell separation was optimized and evaluated in terms of purity, separation efficiency, taxonomic resemblance, and compatibility to high-performance liquid chromatography and mass spectrometry for biomolecule analyses. Because cell extracts from density centrifugation still contained considerable amounts of detrital particles and non-cellular biomolecules, we further purified cells from two samples by fluorescence-activated cell sorting (FACS). Cells from these highly purified cell extracts had an average content of amino acids and lipids of 23–28 fg cell-1 and 2.3 fg cell-1, respectively, with an estimated carbon content of 19–24 fg cell-1. In the sediment, the amount of biomolecules associated with vegetative cells was up to 70-fold lower than the total biomolecule content. We find that the cellular content of biomolecules in the marine subsurface is up to four times lower than previous estimates. Our approach will facilitate and improve the use of biomolecules as proxies for microbial abundance in environmental samples and ultimately provide better global estimates of microbial biomass.
Original languageEnglish
JournalGeochimica et Cosmochimica Acta
Volume188
Pages (from-to)330-351
Number of pages21
ISSN0016-7037
DOIs
StatePublished - 17 Jun 2016

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