Anaerobic magnetite production by a marine, magnetotactic bacterium

Abstract

Bacterial production of magnetite represents a significant contribution to the natural remanent magnetism of deep-sea and other sediments^1–5. Because cells of the freshwater magnetotactic bacterium Aquaspirillum magnetotacticum require molecular oxygen for growth and magnetite synthesis⁶, production of magnetite by magnetotactic bacteria has been considered to occur only in surficial aerobic sediments⁷. Moreover, it has been suggested that deposits of single-domain magnetite crystals are palaeooxygen indicators presumably having been formed under predominantly microaerobic conditions^5–8. In contrast, some nonmagnetotactic, dissimilatory iron-reducing bacteria, such as the recently described strain GS-15 by Lovley et al.⁷, synthesize extracellular magnetite from hydrous ferric oxide under anaerobic conditions. We now report the first isolation and axenic culture of a marine, magnetotactic bacterium, designated MV-1, that can synthesize intracellular, single-domain magnetite crystals under strictly anaerobic conditions. We conclude that magnetotactic bacteria do not necessarily require molecular oxygen for magnetite synthesis and suggest that they, as well as dissimilatory iron-reducing bacteria, can contribute to the natural remanent magnetism of even long-term anaerobic sediments.