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Abstract

Algae produce massive amounts of dimethylsulfoniopropionate
(DMSP), which fuel the organosulfur cycle1,2. On a global scale,
several petagrams of this sulfur species are produced annually,
thereby driving fundamental processes and the marine food web1.
An important DMSP transformation product is dimethylsulfide,
which can be either emitted to the atmosphere3,4 or oxidized
to dimethylsulfoxide (DMSO) and other products5. Here we
report the discovery of a structurally unusual metabolite,
dimethylsulfoxonium propionate (DMSOP), that is synthesized by
several DMSP-producing microalgae and marine bacteria. As with
DMSP, DMSOP is a low-molecular-weight zwitterionic metabolite
that carries both a positively and a negatively charged functional
group. Isotope labelling studies demonstrate that DMSOP is
produced from DMSP, and is readily metabolized to DMSO by
marine bacteria. DMSOP was found in near nanomolar amounts
in field samples and in algal culture media, and thus represents—
to our knowledge—a previously undescribed biogenic source
for DMSO in the marine environment. The estimated annual
oceanic production of oxidized sulfur from this pathway is in the
teragram range, similar to the calculated dimethylsulfide flux to
the atmosphere3. This sulfoxonium metabolite is therefore a key
metabolite of a previously undescribed pathway in the marine sulfur
cycle. These findings highlight the importance of DMSOP in the
marine organosulfur cycle.