Diffusion-controlled metabolism for long-term survival of single isolated microorganisms trapped within ice crystals

Two known habitats for microbial metabolism in ice are surfaces of mineral grains and liquid veins along three-grain boundaries. We propose a third, more general, habitat in which a microbe frozen in ice can metabolize by redox reactions with dissolved small molecules such as CO2, O-2, N-2, CO, and CH4 diffusing through the ice lattice. We show that there is an adequate supply of diffusing molecules throughout deep glacial ice to sustain metabolism for >10(5) yr. Using scanning fluorimetry to map proteins (a proxy for cells) and F420 (a proxy for methanogens) in ice cores, we find isolated spikes of fluorescence with intensity consistent with as few as one microbial cell in a volume of 0.16 mu l with the protein mapper and in 1.9 mu l with the methanogen mapper. With such precise localization, it should be possible to extract single cells for molecular identification.