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Degree

Doctor of Philosophy, Ohio State University, Microbiology, 2002.

Abstract

An extraction system has been constructed that melts ice from the interior of ice cores and collects the resulting melt water aseptically. Using this system, bacteria entrapped in modern and ancient glacial ice from worldwide locations and in an ice core extending into accreted Lake Vostok ice have been isolated using enrichment culture and identified by amplification and sequencing of DNA-encoding 16S rRNA genes. In general, ice cores from non-polar locations contained larger numbers and species of cultivable bacteria than samples from polar ices, presumably due to the closer proximity of terrestrial biological ecosystems and exposed landscape. When compared with other polar locations, higher numbers of isolates were obtained from ices adjacent to the Dry Valley complex of Antarctica, consistent with the influx of airborne biological particles from local environments serving as the primary factor controlling the numbers of microorganisms present. The numbers of recoverable bacteria did not correlate directly with the age of the ice, and isolates were recovered from the oldest samples examined (>500K years old). The 16S rDNA sequences from bacterial isolates and amplicons obtained directly from samples position within 6 different bacterial lines of descent (alpha, beta, and gamma-proteobacteria, high and low G+C gram positive bacteria, and the Cytophaga/Flavobacterium/Bacteroides). Some of the isolated bacteria have close phylogenetic relationships with species originating from permanently cold environments, and other ice core sites or different portions (time periods) of the same core. Macromolecular synthesis was demonstrated in bacteria frozen under conditions analogous to those in glacial ice, and the possibility exists that metabolic activity and repair may occur during extended periods of glacial entrapment. Several of the species identified in Lake Vostok accretion ice are also related to glacial isolates and species from other cold environments. These ice core studies have provided a glimpse of the microorganisms likely to inhabitant this potentially unique subsurface ecosystem. Investigating microbial survival in ice and exploring potential habitats for activity within the glacial and subglacial environment has confirmed that these could have served as refuge environments for life during periods of global glaciation (Snowball Earth), and has provided data for extrapolations to the likelihood of microorganisms surviving frozen in extraterrestrial habitats or during interplanetary transport.

Subject Headings

Biology, Microbiology

Keywords

microbial survival; glacial ice; extreme environment; exobiology; Lake Vostok

Advisor

John N. Reeve

Pages

194p.

Document number: osu1015965965
Permalink: http://rave.ohiolink.edu/etdc/view?acc_num=osu1015965965

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