Isolation and pure culture of a freshwater magnetic spirillum in chemically defined medium

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Abstract
A bipolarly flagellated magnetotactic spirillum containing intracellular chains of single domain-sized magnetite crystals was isolated by applying a magnetic field to sediments from a freshwater swamp. The organism was cultured in a chemically defined medium containing ferric quinate and succinate as sources of Fe and C, respectively. Non-magnetic variants of this isolate were maintained in chemically defined medium lacking ferric quinate. In contrast to magnetic cells, these had less Fe and lacked measurable magnetic remanence and the intracytoplasmic crystals. In other respects, including moles percent G + C content, growth characteristics, nutrition and physiology, the 2 types were similar. The isolate reduced nitrate without accumulating nitrite and produced NO3- during growth. NH3 or NH4+ served as a N source. The organism was microaerophilic and did not grow anaerobically with nitrate in the medium. In chemically defined medium, cells synthesized magnetite only if the initial O2 concentration in the atmosphere of sealed cultures was 6% (vol/vol) or less.