RECONSTRUCTING PAST ECOLOGIES USING PEPTIDOMICS

The project will try to understand what the ocean was like in the past by looking at proteins in mud found at the bottom of the ocean. When marine organisms die they sometimes sink to the bottom of the ocean and their carcasses accumulate in the mud. This happens even for very small organisms, and some of their proteins are left behind.

Like the rings of a tree trunk, sediment at the bottom of the ocean slowly accumulates and acts as a recording of the past. The deeper you go into the sediment the older the proteins are. The study will extract protein from sediment that goes back about 150,000-years.

The proteins will be sorted by the functions the proteins had when they were in the living organism, and by the organisms that they came from. The study should discover hundreds of ancient proteins. Those proteins will provide information about the types of organisms living in the past at that spot and what they were doing.

Those data will make it possible to reconstruct the ecology of the past ocean. The study will use sediments from the Pacific coast of Mexico where conditions are good to preserve proteins, and where the community of microscopic organisms living in the past is expected to be dramatically different from today. The project will support a Mexican-American woman postdoc and a high school internship program.

In that program three high school students from groups underrepresented in the earth sciences will be paired with undergraduate and grad student mentors.

Past ocean environments are often evaluated using specific organic proxies that are linked to important oceanic processes such as primary production. A new tool for reconstructing the past ecology of the water column (e.g. estimating community structure and composition) is proposed. Peptides extracted from a well-characterized marine sediment that extends back into the Last Glacial Maximum will be used to reconstruct the past community ecology of the overlying water.

Simultaneous assessment of the diagenetic status of extracted peptides provides a built-in measure of how much degradation has occurred, allowing for back-calculation of primary production. The development of new peptide-based biomarkers will allow for past oceanic conditions to be assessed in much greater ecological detail, thus enabling better prediction of future change.

Peptides will be extracted from a well-characterized varved sediment core collected in the Eastern Tropical North Pacific along the Baja peninsula. A novel de novo-directed peptidomic approach based on computational analyses of resultant tandem mass spectra will be used to identify peptides in subsamples of the core from the Holocene and the LGM. These are believed to be among the first successful peptide extractions from marine sediments.

The peptides to be evaluated include highly conserved peptides that are found only associated with photosynthesis but are universal across kingdoms. Because these peptides are universal but unique to autotrophs, they serve as a proxy for the total chloroplast (e.g. chlorophyll, primary production) of a sample. Peptides that identify other community functions such as nitrogen fixation and denitrification will also be sought.

The overall peptide composition records a slice in time of the overlying water. The core has a well-constructed age model and has already been analyzed for biogenic silica and pigments, thus providing other measures to compare against. Modern samples of plankton and sinking particles collected at and near the ETNP core location will also be assessed.

The intent is to develop a quantitative understanding of the paleo record that can be extracted from the peptides in the core and relate it back to the processes in the overlying water that deliver the signal to the sediment.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.