| Summary: | Thesis (Ph. D.)--University of Washington, 1996 Over 250 gas vesicle producing (gas vacuolate) bacteria have been isolated from arctic and antarctic sea ice and water (Irgens et al., 1989; Staley et al., 1989; Gosink et al., 1993; Gosink and Staley, 1995). These strains are the first reported examples of heterotrophic gas vacuolate bacteria from a marine environment and the first reported examples of gas vacuolate bacteria from the beta Proteobacteria and Cytophaga/Flavobacteria/Bacteroides (CFB) phylogenetic groups (Gosink and Staley, 1995). Investigation of these isolates tested three hypotheses: (1) that there are several distinct groups of gas vacuolate bacteria associated with the sea ice; (2) that the species of gas vacuolate bacteria from the Arctic and Antarctic are biogeographically distinct; and (3) that the gas vesicle phenotype in polar isolates, particularly among CFB members, is the result of a recent horizontal gene transfer event. The results of this study show that several distinct groups of gas vacuolate bacteria can be cultivated from the north and south polar regions, each representing a unique species. Because none of the isolates were of the same species, there is no evidence for cosmopolitan species of polar gas vacuolate bacteria. Due to an unexpectedly high level of species diversity, however, insufficient numbers of any one group were sampled to demonstrate exclusive species in either the Arctic or Antarctic. Analysis of the CFB gas vesicle structural gene (gvpA) sequences showed that they formed a monophyletic clade that was not associated with any other gvpA sequences. This suggests that gvpA was not acquired by a recent horizontal gene transfer event in these species.
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