Date of Award

Spring 1991

Project Type

Dissertation

Program or Major

Microbiology

Degree Name

Doctor of Philosophy

First Advisor

Richard P Blakemore

Abstract

Of the many diverse forms of magnetotactic bacteria found in nature, very few have been isolated in axenic culture. Consequently, it has not been possible to address by conventional microbiological techniques the extent of phylogenetic conservation of magnetotaxis among prokaryotes. Modern methods of DNA amplification combined with nucleotide sequence analysis were considered, at the inception of this study, to provide a means of addressing phylogenetic relatedness among magnetotactic bacteria in the absence of axenic cultures. Analysis was made of the 16S ribosomal RNA of Aquaspirillum magnetotacticum strain MS1 and Bilophococcus magnetotacticus, to initiate phylogenetic characterization of magnetotactic organisms. These freshwater magnetotactic bacteria were found to belong to the proteobacteria group of Eubacteria. A. magnetotacticum grouped specifically among the alpha-proteobacteria while B. magnetotacticus branched deeply within the proteobacteria, but did not fall within either the alpha, beta, delta, or gamma groupings. These findings indicated that prokaryotic intracellular magnetosome formation and magnetotaxis might be limited to proteobacteria. However, considerable divergence between A. magnetotacticum and B. magnetotacticus suggests that magnetogenesis may be a relatively widespread trait, which is indicative of a primitive adaptation. Additional ribosomal RNA sequence information from diverse forms of magnetotactic prokaryotes, as well as detailed understanding of the molecular pathways responsible for prokaryotic magnetogenesis is needed to elucidate the evolution and phylogenetic distribution of the prokaryotic magnetotactic phenotype.

Biological magnetite synthesis by magnetogenic organisms such as A. magnetotacticum MS1 has potential industrial significance. Magnetite biogenesis can be exploited only if the molecular biology responsible for magnetosome synthesis is understood and easily manipulated. To this end, a plasmid transfer system was constructed for several members of the genus Aquaspirillum. A gene transfer system which might potentially provide access to magnetosome-encoding genomic sequences was sought as a means of better understanding the genetic basis of magnetogenesis.

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