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Magnetotactic bacteria and their mineral inclusions from Hungarian freshwater sediments

2000; Volume: 43; Issue: 4 Linguagem: Inglês

1588-2594

Mihály Pósfai, Balázs Arató,

Geology and Paleoclimatology Research

Magnetotactic bacteria produce nano-scale, intracellular magnetic minerals. The study of such minerals is of interest because it can shed light on biogenic mineral-forming processes, and on the potential contribution of biomagnets to the magnetic signal of sediments and rocks. We collected sediment and water samples from several Hungarian lakes and streams. Magnetotactic bacteria were present in all studied environments; in some samples they occurred in such large numbers that their mineral inclusions likely represent a major source for sediment magnetism. After magnetic enrichment of magnetotactic species, we characterized distinct morphological types using a light microscope. Our systematic study showed that a few bacterium types are widespread in most of the studied freshwater environments. Using transmission electron microscopy, we studied the composition, microstructure, sizes and habits of magnetite particles from a helicoid magnetotactic bacterium from Gyongyos stream, Szombathely. Size and shape distributions of the intracellular crystals show some distinct features that may be used for distinguishing bacterial from nonbiogenic magnetite and for identifying possible mechanisms of crystal growth. In particular, the crystal size distribution (CSD) curve is highly asymmetric, consistently with previous observations on magnetite from magnetotactic bacteria. The asymmetry and our new observation of two maxima in the CSD suggest that Ostwald ripening and crystal agglomeration played important roles in the formation of the nanoscale magnetite particles.