Materials are sealed in and preserved by limiting their contact with air and water. We can then assume that retaining the same preservation models, the bacteria in ice could possibly have been conserved as inactive spores for as far back as our glacial records begin. Conversely, we should add that not all bateria have the capabilities of forming protective spores, and therefore only select species may be conserved through extremes. To relate these to quaternary ice formations, snow algae has indeed been conserved in ice, as we have seen in ice cores. Since most articles where passed on to me by colleagues, some articles have incomplete references.
All pertinent information is cited here.
For further consultation, I have the articles at my disposition. Richard Hoover, Taken from In Brief in EOS, Vol. 79, Number 14 April 7, 1998,n.p.