Life in solid ice

Some microbes appear to be able to metabolize in glacial ice or permafrost. The rate depends on temperature, nutrient level and bioelement availability, among other factors. I have developed a plausible argument that they do this while confined in veins filled with acidic or saline solution that provides nutrients and elements necessary for growth (78). Here I develop this scenario further and discuss some of its implications for ice-covered planetary bodies and for the origin of life. An accompanying paper (7) discusses plans to test this hypothesis using epifluorescence microscopy of pristine (unmelted) ice samples and an optical biospectrologging tool to assay living and dead microbes in a borehole in glacial ice. Table 1 lists some of the data on concentrations of bacteria and archaea, especially those that live in low-temperature environments. Bacteria are found essentially everywhere on earth in concentrations that do not vary by more than a few orders of magnitude. Archaea are generally nearly as abundant as bacteria when methods for identifying them are used. Table 2 lists some of the types of microbial life found in glacial and permafrost ice. Challenges to survival include extremes of temperature, pressure, pH, dryness, salinity, oxygen concentration, radiative flux (including sunlight), and availability of nutrients and bio-elements. Glacial ice provides a time machine from which can be extracted microorganisms of known age, whose response to extreme cold and lack of nutrients can be studied. One of the unsolved problems in microbiology is the length of time in conditions of extreme temperatures and nutrient deprivation over which microorganisms can remain viable. No one has yet carried out a thorough study of the depth-dependence of the types of microbes or of the fractions that were viable and metabolizing, that were viable but not culturable, that were dormant, and that were dead. In fact, the definition of " death " may require revision as techniques for cultivating microbes found in ice improve. We first discuss studies of microbes as a function of depth in the deep Vostok ice core. Abyzov et al. (2) searched for microbes at intervals of ~100 m at depths from 1500 to 2750 m in glacial ice from the Vostok core by passing melted ice through 0.2 µm filters. They reported concentration vs depth, studied morphology with SEM and epifluorescence microscopy of stained samples, and studied the fraction of viable organisms in various nutrients. The great majority of the …