LexEn Collaborative research: Glacial "hitchhiking:" A mechanism for bacterial speciation in an extremely cold environment Principal Investigator: Wade H. Jeffrey, PhD Co-Principal Investigator: David L. Mitchell, PhD. MD Anderson Cancer Center, Smithville, TX Support Agency: National Science Foundation Location of Study: Polar Glacial Ice Samples

Bacteria are "hitchhikers" in glaciers; deposited from above on windborne dust particles and aerosols, overlayered by thousands of years of deposition and accretion, and finally returned to the coastal marine environment by glacial calving and melting. Bacteria have been detected in and cultured from glacial ice ranging from a few hundred to many thousands of years old. Evidence suggests that glacial ice cannot support bacterial growth but rather traps these organisms for considerable lengths of time in an anabiotic state. In the absence of DNA replication and repair, we hypothesize that DNA degradation occurs at a significant rate and that base modifications resulting from spontaneous depurinations, depyrimidinations, and deaminations accumulate. Although much of the DNA degradation would be lethal to dividing bacteria, it is probable that organisms that are successful in recovering from the ice replicate their DNA using a template containing significant levels of base modifications; this would lead to a significant mutation frequency.
In the context of "glacial hitchhiking", we propose to test the hypothesis that bacteria sustain significant levels of base damage during glacial entrapment and that this base damage leads to mutations. In the course of our studies we will culture, preserve, and characterize a diverse array of bacteria extracted from glacial ice. We will examine the lethal effects of glaciation on bacteria using clonability, transcription, protein synthesis, and fluorescence in situ hybridization using rRNA probes as biological endpoints. Mutations will be analyzed as heteroduplex molecules formed after an incipient round of DNA replication using immoblized mismatch binding protein (mutS). From our work we will gain insight into basic mechanisms of mutagenesis that may be relevant to bacterial speciation, diversity and the evolution of life on earth as well as in extremely cold environments found elsewhere in our solar system. We also expect to show a correlation between DNA damage, cell lethality, and mutagenesis with respect to time spent in the glacier, thus providing a novel and facile approach for ice core dating.