An integrated approach for ecological, cultivational, ultrastructural, and genomic analysis of the uncultivated giant magnetotactic rod cand. "Magnetobacterium bavaricum"

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Magnetotactic bacteria (MTB) are a highly diverse group of aquatic procaryotes whose swimming motility is directed by complex intracellular magnetic organelles, the magnetosomes, which are formed by controlled biomineralization. Despite of their ecological importance and abundance in many aquatic ecosystems, their biology has remained largely unknown, since most MTB from natural populations have resisted conventional attempts of isolation. We plan to characterize the uncultivated magnetotactic rod cand. “Magnetobacterium bavaricum”, which is distinct from all other known MTB by its unique affiliation with the deep-branching Nitrospira group, its complex cell biology and large size, and its ability to biomineralize up to 1000 bullet-shaped magnetite crystals. In the proposed project we plan to investigate its ecology, physiology, cell biology and genetic characteristics by using an integrated approach comprising a set a of innovative methods. Geochemical characteristics obtained by microelectrode measurements from two freshwater sampling sites including a dedicated mesocosm will be correlated with the abundance and spatial distribution of cells. Cells of M.bavaricum will be magnetically enriched from environmental microcosms for thorough ultrastructural analysis by various methods including cryo-sectioning and FIB-milling followed by SEM and electron tomography. We will establish the prerequisites for partial and, ultimately, complete genome analysis of M. bavaricum. First, genomic DNA isolated from collected cells will be used for the construction of large-insert fosmid libraries that will be screened for homologs of known magnetosome island gene clusters. Second, cells selected by micromanipulation will be employed in whole genome amplification experiments, and amplified DNA will be subjected to pyrosequencing. Finally, results from ecological and genomic characterization will be used to guide a high-throughput cultivational approach.