Properties of intracellular magnetite crystals produced by Desulfovibrio magneticus strain RS-1

Abstract

Desulfovibrio magneticus strain RS-l is an anaerobic sulfate-reducing bacterium. Cells form intracellular nanocrystals of magnetite but are only weakly magnetotactic. In order to understand the unusual magnetic response of this strain, we studied magnetite crystals within cells grown with fumarate and sulfate. Many cells grown under either condition did not form magnetic crystals while others contained only 1 to 18 small (~40 nm) magnetite-containing magnetosomes. Bulk magnetic measurements of whole cells showed a superparamagnetic-like behavior, indicating that many of the magnetite crystals are too small to have a permanent magnetic moment at ambient temperature. The temperature of the Verwey transition is lower (~ 86 K) than of magnetite from other magnetotactic strains, likely indicating partial oxidation of magnetite into maghemite. As a result of the small size and small number of magnetite magnetosomes, the magnetic moments of most cells grown anaerobically with fumarate or sulfate are insufficient for magnetotaxis.In addition to intracellular magnetite, in some cultures another iron oxide, hematite, formed on the surfaces of cells. The hematite grains are embedded in an extracellular polymeric material, indicating that the crystals likely resulted from a biologically induced mineralization process. Although the hematite particles appear to consist of aggregations of many small (5 to 10 nm) grains, the grains have a consensus orientation and thus the whole particle diffracts as a single crystal. The aligned arrangement of nanoparticles within larger clusters may reflect either a templated nucleation of hematite crystallites in an extracellular organic matrix, or result from a self-assembling process during the crystallization of hematite from ferric gels or ferrihydrite.

Ecology, Diversity, and Evolution of Magnetotactic Bacteria

“…To obtain a stronger magnetotactic response, the iron concentration was increased from 20 to 200 M, and the headspace of the cultures was purged every other day with oxygen-free argon gas in order to decrease the concentration of hydrogen sulfide in the cultures (28). This issue of iron availability may be true for other sulfatereducing MTB such as Desulfovibrio magneticus, since this organism produces very few magnetosomes when grown anaerobically with sulfate compared to growth with fumarate (63). When a culture of the magnetite-and greigite-producing organism "Ca.…”

Formation of magnetite by bacteria and its application

“…The production of BacMPs within the RS-1 strain is substrate dependent, whereby RS-1 cells produced an average of six BacMPs per individual cell when fumarate was used as an electron acceptor, while almost no BacMPs were produced when sulphate was used. This bacterium also produces extracellular magnetic iron sulphide ) and hematite (Posfai et al 2006) on its surface. Magnetotaxis in the RS-1 strain is distinctly different from that in the other strains of magnetotactic bacterial cells that swim or orient themselves along a single direction on applying a magnetic field.…”

Whole genome sequence of Desulfovibrio magneticus strain RS-1 revealed common gene clusters in magnetotactic bacteria

“…Strain RS-1 therefore represents a bacterium with a novel metabolic feature among the magnetotactic bacteria (Sakaguchi et al 2002). Moreover, this bacterium synthesizes irregular bullet-shaped magnetite crystals; the crystals are morphologically irregular, but share distinct crystallographic characteristics (Posfai et al 2006), suggesting the presence of a unique biological regulation system of crystal morphology (Sakaguchi et al 2002).…”