Magnetite (Fe₃O₄) and Greigite (Fe₃S₄) Crystals in Multicellular Magnetotactic Prokaryotes

Magnetotactic bacteria produce iron oxides, iron sulfides or both in organelles called magnetosomes. Most of these bacteria are unicellular and biomineralize magnetite (Fe₃O₄). In contrast, multicellular magnetotactic prokaryotes (MMPs) consisting of several gram-negative cells have only been known to crystallize the magnetic iron sulfide greigite (Fe₃S₄). In this work, we describe MMPs that mineralize magnetite in bullet-shaped crystals. Another unusual aspect is that magnetite occurs either as the only crystals or together with greigite crystals. MMPs containing only greigite in the magnetosomes occur in the same environment. These findings show that morphology, ultrastructure, and behavior are the main characteristics of the MMPs, not the type of magnetic crystal biomineralized in the magnetosomes.

Keywords:

• biomineralization
• greigite
• magnetite
• magnetosome
• magnetotactic bacteria
• magnetotactic multicellular organism
• multicellular magnetotactic prokaryote
• manycelled magnetotactic prokaryote
• MMP

Acknowledgments

We thank Dr. Laurence Garvie for help with EELS analysis and Dr. István Dódony for help with HRTEM imaging. Electron microscopy using the Philips EM400ST and TOPCON2B was done at ASU. Partial financial support came from Brazilian Agencies FUJB, FAPERJ, CAPES and CNPq, and also from TWAS. UL acknowledges support from a NASA grant to PRB.