"What mammalian species would be most suited to live on a teraformed Mars. Primarily as a source of protein for humans"
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What are the Mg Isotopic-Signals for Photosynthesis?
PI: Casey, Bill
We propose research to assess whether Mg-isotope geochemistry can be used to detect the signal of photosynthesis, which addresses goals in the Astrobiology program to identify the signals for early life. We recently discovered that biosynthesis of chlorophyll-a in Synechococcus elongatus, a unicellular cyanobacterium, induces a distinct Mg-isotope fractionation. Magnesium extracted from chlorophyll-a is depleted in the heavier isotopes, relative to magnesium in the culture media. This fractionation may be common to all photosynthetic organisms, and, thus, global in extent. We propose a series of tasks to establish this fact.
The research is guided by two hypotheses. First, is the Mg-isotope fractionation occuring during the insertion of Mg(II) into the Protoporphyrin IX molecule, which is a tetrapyrrole that is common to the synthetic pathways for both chlorophyll and heme? To test this hypothesis, we propose to show that Mg-isotopic fractionation is insensitive to the taxonomy of the organism in a series of lab and field measurements where the pigments are separated and the Mg-isotopic compositions compared. We are also examining whether the recycling of Mg in photo-damaged chlorophyll allows for isotopic equilibrium to be established.
Our second hypothesis is that the pool of metal for pigment synthesis is recycled in magnesium-poor environments. The record of Mg-isotopes in chlorophyll in such an environment would then reflect Rayleigh distillation of the bioavailable magnesium isotopes, since chlorophyll biosynthesis favors lighter isotopes over heavy isotopes of magnesium. If so, then we expect to see different Mg-isotope values, and ranges of values, in environments that differ only in magnesium bioavailability.
Photosynthesis accounts for ~100 gigatons of carbon per year on Earth, which is fundamental to all geochemical cycles. Magnesium is the metal center in the chlorophyll molecule and thus is central to the history and geochemistry of life on the planet, and perhaps others.
