Desulfovibrio magneticus sp. nov., a novel sulfate-reducing bacterium that produces intracellular single-domain-sized magnetite particles

Researchers isolated a novel sulfate-reducing bacterium designated strain RS-1T from freshwater sediments in Japan. Using 16S rRNA gene sequencing and other molecular analyses, they determined this organism belongs to the genus Desulfovibrio and represents a new species, named Desulfovibrio magneticus. The bacterium is unique among known Desulfovibrio species for producing intracellular magnetite particles (magnetosomes) that range from bullet-shaped to irregular in morphology. D. magneticus is a strict anaerobe that uses lactate, pyruvate, and other organic acids as electron donors while reducing sulfate, thiosulfate, or fumarate. Notably, the bacterium produces significantly more magnetite particles when fumarate rather than sulfate serves as the electron acceptor, with approximately 70% of cells displaying magnetotaxis under fumarate-reducing conditions versus less than 1% under sulfate reduction. The organism contains desulfoviridin and c-type cytochromes and uniquely carries menaquinone MK-7(H₂) instead of the MK-6 variants found in other Desulfovibrio species. Growth occurs optimally at 30°C and pH 7.0 in freshwater medium.

Key findings

• D. magneticus is the first known dissimilatory sulfate-reducing bacterium capable of synthesizing intracellular magnetite particles.
• Magnetite particle production is significantly enhanced when fumarate is used as electron acceptor (mean of 6 particles per cell) compared to sulfate, and magnetotaxis frequency increases accordingly.
• The bacterium possesses menaquinone MK-7(H₂), distinguishing it from all other characterized Desulfovibrio species which contain MK-6 variants.
• Phylogenetic analysis places D. magneticus in the δ-Proteobacteria genus Desulfovibrio, with 98.7% similarity to D. burkinensis but only 51% DNA-DNA hybridization, confirming it as a distinct species.