Item

Abstract

Microbial communities exchange molecules with their environment, which
plays a major role in regulating global biogeochemical cycles and
climate. While extracellular metabolites are commonly measured in
terrestrial and limnic ecosystems, the presence of salt in marine
habitats limits the nontargeted analyses of the ocean exometabolome
using mass spectrometry (MS). Current methods require salt removal prior
to sample measurements, which can alter the molecular composition of the
metabolome and limit the types of compounds detected by MS. To overcome
these limitations, we developed a gas chromatography MS (GC-MS) method
that avoids sample altering during salt removal and that detects
metabolites down to nanomolar concentrations from less than 1 ml of
seawater. We applied our method (SeaMet) to explore marine metabolomes
in vitro and in vivo First, we measured the production and consumption
of metabolites during the culture of a heterotrophic bacterium,
Marinobacter adhaerens Our approach revealed successional uptake of
amino acids, while sugars were not consumed. These results show that
exocellular metabolomics provides insights into nutrient uptake and
energy conservation in marine microorganisms. We also applied SeaMet to
explore the in situ metabolome of coral reef and mangrove sediment
porewaters. Despite the fact that these ecosystems occur in
nutrient-poor waters, we uncovered high concentrations of sugars and
fatty acids, compounds predicted to play a key role for the abundant and
diverse microbial communities in coral reef and mangrove sediments. Our
data demonstrate that SeaMet advances marine metabolomics by enabling a
nontargeted and quantitative analysis of marine metabolites, thus
providing new insights into nutrient cycles in the oceans.IMPORTANCE
Nontargeted approaches using metabolomics to analyze metabolites that
occur in the oceans is less developed than those for terrestrial and
limnic ecosystems. One of the challenges in marine metabolomics is that
salt limits metabolite analysis in seawater to methods requiring salt
removal. Building on previous sample preparation methods for
metabolomics, we developed SeaMet, which overcomes the limitations of
salt on metabolite detection. Considering that the oceans contain the
largest dissolved organic matter pool on Earth, describing the marine
metabolome using nontargeted approaches is critical for understanding
the drivers behind element cycles, biotic interactions, ecosystem
function, and atmospheric CO2 storage. Our method complements both
targeted marine metabolomic investigations as well as other "omics"
(e.g., genomics, transcriptomics, and proteomics) approaches by
providing an avenue for studying the chemical interaction between marine
microbes and their habitats.