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Project Progress

We are examining the diversity of psychrophilic (cold-loving) microorganisms as models for the possible origin, evolution, and survival of organisms from other cold, non-terrestrial sources. Of specific interest to NASA is our analysis of the microbial diversity of an ice core taken from a > 120,000 year old Greenland glacier ice core sample. Epifluorescence microscopy showed that the ice sample contained over 60 million cells/ml. We inoculated a sterile, melted sample into anaerobic media and incubated cultures for several months at minus 2°C. The microorganisms in this sample were characterized in two ways. First, deoxyribonucleic acid (DNA) was extracted from the community and the ribosomal ribonucleic acid (rRNA) gene polymerase-chain-reaction (PCR) amplified. Approximately 60 bacterial inserts were screened by restriction endonuclease analysis and grouped into 27 unique types, and 24 sequences were compared phylogenetically. These sequences represented a wide physiological diversity, including Gram positive anaerobic rods and cocci and alpha, beta, and gamma Proteobacteria. In our second approach, we cultivated nearly 800 hundred aerobic isolates, many with pigmented and different colony morphologies. We amplified, cloned, and aligned rRNA gene sequences for 28 of these isolates. Phylogenetic analyses showed representatives from many different physiological groups, many of which had not been represented in the clone library. Several conclusions derive from these results. A rich, viable, microbial diversity was preserved in the >120,000 year old ice core. Both the extraction of DNA and isolation of organisms are needed to provide a comprehensive view of the microbial diversity. Many rRNA genes differed from known sequences and may represent the discovery of novel genera or families. Anaerobic incubation may aid the recovery of isolates that cannot grow when taken directly from the ice core sample. Further studies are important for understanding the possible existence, survival, and recovery of organisms in other extremely cold environments.