Researchers in computational biology and marine science have combined their diverse expertise and found that trace-metal usage by present-day organisms probably derives from major changes in ocean chemistry occurring over geological time scales.
|Dust storms sweep iron-rich particles (mineral aerosols) from the continents into the atmosphere. They fall into, or are rained into, the oceans, where iron dissolves into a form that is used, along with other nutrients such as nitrate (N) and phosphate (P), by phytoplankton and bacteria to live and grow. Small marine animals (zooplankton) eat phytoplankton and bacteria. When they excrete fecal pellets or die, organic matter is transferred to the depths.
Credit: Jack Cook, Woods Hole Oceanographic Institution
Using protein structures for the first time in such a study, the research establishes one of the influences that geochemistry has had upon life.
The study, published in the Proceedings of the National Academy of Sciences, sought to verify the theory that the rise in atmospheric oxygen some 2.3 billion years ago, and attendant shifts in ocean chemistry, led to changes in types of metals used with protein structures. Such changes are hypothesized to have led to the diversification and increased complexity of the life we see today.
Scientists Chris Dupont, Song Yang, Brian Palenik and Philip Bourne from the San Diego Supercomputer Center (SDSC), Scripps Institution of Oceanography, and the departments of chemistry and biochemistry and pharmacology at the University of California, San Diego (UCSD) analyzed the metal-binding characteristics of all known protein structures found in all kingdoms of life.
Protein structures are ideal for this study, Bourne said, since they are much more conserved than protein sequences, traditionally used in such studies and, furthermore, metal binding can be inferred directly.
Using data generated by Dupont and Yang, the group established that the three superkingdoms of life Archaea, Bacteria and Eukarya -- all use metals differently. The differences reflect the availability of such metals in the ocean as the respective superkingdoms evolved.
The authors conclude that, these conserved trends are proteomic imprints of changes in trace-metal bioavailability in the ancient ocean that highlight a major evolutionary shift in biological trace-metal usage.
|Tree of life, divided between three major cell types, those with and without a nucleus (Bacterial Prokaryotes and Animal Eukaryotes), preceded by the root of the tree, Archea.
The changes in trace-metal availability are believed to have been brought about by the biologically caused rise in atmospheric oxygen some 2.3 billion years ago, highlighting the co-evolution of biology and geochemistry on a global scale.
Here, a biological phenomenon, photosynthesis, changed the availability of trace metals in the oceans, Dupont said, resulting in a reciprocal change in biological evolution still observable today.
The group notes that, such studies linking the study of the earth sciences with that of the life sciences are limited and certainly no one has previously looked at this exciting area from the perspective of protein structure. We hope this will encourage others to undertake such interdisciplinary work.
Such interdisciplinary studies are of immense interest to astrobiology and will help to clarify the connections between historic changes in the Earth's environment and the evolution of life.