I dedicate this talk to Stanley Miller, a principal proponent of the view that life evolved in an icy environment. I will discuss our development of a new method to study evolution of bacteria over hundreds of millions of generations by analyzing changes in the genomes of cells frozen in several-thousand-meter ice cores. Their evolution in oceans is fast due to horizontal gene transfer during encounters of cells with each other. My student Ajeeth Adhikari and our collaborators Giovannoni and Vergin at Oregon State and Morris at Michigan State are developing techniques for studying evolution of submicron-size cells in ice, with age increasing through an ice core.            In 2000 I showed that polycrystalline ice is filled with liquid veins of diameter a few �m governed by the concentration of soluble impurities at grain boundaries, typically sulfuric acid, and containing bacteria trapped in the veins during grain development. Many of them adapt to the low pH and extract metabolic energy from the veins.            The most abundant microorganisms in today's oceans are the chlorophyll-bearing picocyanobacteria Prochlorococcus (Pro) and Synechococcus (Syn), which are the most ancient aerobes (origin ~3 Gyr ago). Most marine biologists still think they are confined to latitudes 40�N to 40�S. However, using flow cytometry to search for bacteria in cores drilled into glacial ice, we found that Pro and Syn are present at all depths in ice cores from Antarctica and Greenland, as a consequence of turbulent wind transport. ~2% of all bacteria in ice are Pro and Syn, and we have recently shown that their genomes change with depth and thus with age. Those two genera are the easiest to identify for genomic analysis because of their bright autofluorescence. Evolution of other bacteria wind-borne onto growing ice from oceans can also be studied.

Record of microbial evolution preserved in pure glacial ice

248th National Meeting (2014)

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