Complete Sequencing and Comparative Analysis of the Genomes of the First Magnetotactic Gammaproteobacteria Isolated in Pure Culture: Strains BW-2 and SS-5

The genomes of the first two discovered magnetotactic bacteria (MTB) belonging to the ammaproteobacteria, strains BW-2 and SS-51, were sequenced, sealed, annotated and compared to MTB of other phylogenetic groups. Cells of both strains are rod-shaped and biomineralize cuboctahedral and elongated octahedral crystals of magnetite, respectively, that are enveloped in a protein-embedded, lipid-bilayer membrane referred to as the magnetosome membrane or vesicle. The crystals and their associated membranes are known as magnetosomes. Magnetosome crystals consist of either magnetite (Fe3O4) or greigite (Fe3S4) and, because of their specific mineral compositions, crystal morphologies and sizes, the biomineralization processes involved in magnetosome formation are thought to be under strict genetic and (bio)chemical control through the action of the proteins associated with the magnetosome membrane. These biomineralization proteins are referred to as the Mam and Mms proteins, and the genes encoding them, the mam or mms genes. Known species of MTB phylogenetically belong to the Alpha-, Gamma-, and Deltaproteobacteria subgroups of the Proteobacteria phylum, the Nitrospira phylum and the candidate phyla Latescibacteria (WS3) and Omnitrophica (OP3). Complete or partial genomes sequences are available for MTB of most of these phylogenetic groups. A notable exception is genomic sequences from MTB from the Gammaproteobacteria. The focus of this doctoral dissertation is the presentation of the first complete genome sequences of gammaproteobacterial MTB as well as a comparison of the genomes and, in particular, a comparison of the magnetosome genes of MTB of other phylogenetic groups. Specific goals were to determine the origin and evolution of the magnetosome genes as well as to determine the metabolic potential of these MTB strains. The genomes of strains BW-2 and SS-5 are 4,103,727 bp and 3,729,439 bp in size, respectively, containing 3,838 and 3,724 coding sequences, respectively. Magnetosome genes form a single cluster about 32,781 kb in length in the genome of strain BW-2, while magnetosome genes make up two clusters in the strain SS-5 genome, of about 29,446 and 5,034 kb in length. Interspersed among the magnetosome genes of both MTB strains are unique coding sequences that share high homology to uncharacterized, hypothetical magnetosome-associated genes of other MTB. As to general metabolism, the genomes of both MTB strains contain the genes necessary for the utilization of the Calvin-Benson-Bassham cycle for autotrophy as well as the genes necessary for the oxidation of reduced sulfur compounds as a source of electrons. This is consistent with their ability to grow as microaerophilic chemolithoautotrophs using thiosulfate and sulfide as electron donors. Finally, numerous sets of genes are present in both genomes that explain other important and minor metabolic features of the strains. In this work genes common to octahedral magnetite producers across phylogenetic groups are identified as well as potential uncharacterized magnetosome genes and the mode of acquisition and molecular evolution of the phenotype across phylogenies will be assessed