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Title: Searches for Microbial Cells with Fluorescence Loggers with Single-cell Sensitivity
Author: Price, P.B., Rohde, R.A. and Bay, R.C.
Periodical: American Geophysical Union, Fall Meeting 2007, abstract #C33B-08
Abstract: Two known habitats for microbial metabolism in ice are surfaces of mineral grains and liquid veins along three- grain boundaries. Several problems suggest the need for a third habitat: veins usually contain toxic liquid; some microorganisms are too large to fit into a vein; veins may not be present at all depths; and the oxygen concentration in veins does not permit the coexistence of both strict anaerobes and aerobes in the same region. We show that a more general habitat avoids these problems. Isolated microbes frozen in ice and not in contact with a vein or grain can metabolize by redox reactions with dissolved small molecules diffusing through the ice lattice. The two requirements are that the gaseous reactants have sufficiently high equilibrium concentrations and diffusion coefficients to provide enough metabolic energy to repair macromolecular damage as it occurs. Molecules with less than ~6 atoms (e.g., H2, O2, N2-, CO, CO2, CH4, H2S, NH3, HNO3, HCHO, and HCOOH) have values of diffusion coefficient D(T) that exceed ~10- 15 m2 s-1, which is sufficient to sustain microbial life in ice. For terrestrial environments, we show that there is an adequate supply of such molecules diffusing throughout deep glacial ice to sustain metabolism for millions of years. Our recent noninvasive observations of ice cores from GISP2 and WAIS Divide provide evidence for this habitat. 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 consistent with as few as one microbial cell in a volume 0.16 microliter with the protein mapper and in 1.9 microliter with the methanogen mapper. With such precise localization one could use a nanomanipulator to extract single cells for molecular identification. Low- power, miniaturized versions of these instruments could search for single cells in subglacial lakes, Martian ice- rich permafrost, and Europan ice.
Year: 2007