Project description:Peptides and proteins were identified using a novel de novo-discovery approach in suspended and sinking organic particles from the eastern tropical North Pacific and in a culture of a dominant autotroph from the region, the cyanobacterium Prochlorococcus. De novo peptide sequencing, where the sequence of amino acids is determined directly from mass spectra rather than from comparison to theoretical spectra from a selected sequence database, was found to be a useful tool for discovery of peptides present in a sample but not initially included in the search database. Iterative de novo-informed database search results suggested the presence of fungal peptides and proteins in deep sinking particles, consistent with growing evidence that fungi play an important role in degradation of sinking material in the ocean. The de novo-discovery approach also allowed the tracking of modified autotrophic cyanobacterial peptides to the deep sea, where they contributed 0.63% of the phylum-level identifiable peptide pool in a bathymetric sediment trap sample. Overall, the amino acid composition of the peptides in the sinking material showed little change with depth, consistent with earlier observations of bulk organic matter and/or amino acid composition during the early stages of degradation. However, we identified an abundance of modified amino acids in sinking and suspended particles, including high levels of deamidation, suggesting that partial degradation of protein could potentially fuel observed anammox and contribute to observed pool of refractory organic nitrogen. We also observe methylation of arginine, which has previously been shown to slow degradation of peptides in seawater. Our results demonstrate several examples how de novo-discovery allows for a deeper evaluation of proteins and peptides in environmental systems undergoing degradation.
Project description:Untargeted proteomics from a 5,000 km+ transect across the central Pacific Ocean from Hawaii to Tahiti. The expedition crossed multiple biogeochemical provinces, inlcuding the oligotrophic North Pacific Subtropical Gyre, the extremety of the Eastern Tropical North Pacific Oxygen Deficient Zone, and the relatively productive equatorial region associated with upwelling. This dataset focuses on the microbial fraction (0.2-3.0 micrometer filter size) and the microbial community dynamics across these biogeochemical provinces, from the surface oceance to the mesopelagic (1,250 m depth maximum).