Abstract
Metaproteomics is one of a suite of new approaches providing insights into the activities of
microorganisms in natural environments. Proteins, the final products of gene expression, indicate
cellular priorities, taking into account both transcriptional and posttranscriptional control
mechanisms that control adaptive responses. Here, we report the proteomic composition of the
o 1.2 lm fraction of a microbial community from Oregon coast summer surface waters, detected
with two-dimensional liquid chromatography coupled with electrospray tandem mass spectrometry.
Spectra corresponding to proteins involved in protein folding and biosynthesis, transport, and viral
capsid structure were the most frequently detected. A total of 36% of all the detected proteins were
best matches to the SAR11 clade, and other abundant coastal microbial clades were also well
represented, including the Roseobacter clade (17%), oligotrophic marine gammaproteobacteria
group (6%), OM43 clade (1%). Viral origins were attributed to 2.5% of proteins. In contrast to
oligotrophic waters, phosphate transporters were not highly detected in this nutrient-rich system.
However, transporters for amino acids, taurine, polyamines and glutamine synthetase were among
the most highly detected proteins, supporting predictions that carbon and nitrogen are more limiting
than phosphate in this environment. Intriguingly, one of the highly detected proteins was methanol
dehydrogenase originating from the OM43 clade, providing further support for recent reports that
the metabolism of one-carbon compounds by these streamlined methylotrophs might be an
important feature of coastal ocean biogeochemistry.
