Magnetotactic bacteria (MTB) are a diverse group of microorganisms with the ability to orient and migrate along geomagnetic field lines. This unique feat is based on specific intracellular organelles, the magnetosomes, which, in most MTB, comprise nanometer-sized, membrane bound crystals of magnetic iron minerals and organized into chains via a dedicated cytoskeleton. Because of the special properties of the magnetosomes, MTB are of great interest for paleomagnetism, environmental magnetism, biomarkers in rocks, magnetic materials and biomineralization in organisms, and bacterial magnetites have been exploited for a variety of applications in modern biological and medical sciences. In this paper, we describe general characteristics of MTB and their magnetic mineral inclusions, but focus mainly on the magnetosome formation and the magnetisms of MTB and bacterial magnetosomes, as well as on the significances and applications of MTB and their intracellular magnetic mineral crystals.

The widely distributed Acidithiobacillus ferrooxidans (A. ferrooxidans) lives in extremely acidic conditions by fixing CO and nitrogen, and by obtaining energy from Fe oxidation with either downhill or uphill electron transfer pathway and from reduced sulfur oxidation. A. ferrooxidans exists as different genomovars and its genome size is 2.89-4.18 Mb. The chemotactic movement of A. ferrooxidans is regulated by quorum sensing. A. ferrooxidans shows weak magnetotaxis due to formation of 15-70 nm magnetite magnetosomes with surface functional groups. The room- and low-temperature magnetic features of A. ferrooxidans are different from other magnetotactic bacteria. A. ferrooxidans has potential for removing sulfur from solids and gases, metals recycling from metal-bearing ores, electric wastes and sludge, biochemical production synthesizing, and metal workpiece machining.

Bacterial magnetosome, synthetized by magnetosome-producing microorganisms including magnetotactic bacteria (MTB) and some non-magnetotactic bacteria (Non-MTB), is a new type of material comprising magnetic nanocrystals surrounded by a phospholipid bilayer. Because of the special properties such as single magnetic domain, excellent biocompatibility and surface modification, bacterial magnetosome has become an increasingly attractive for researchers in biology, medicine, paleomagnetism, geology and environmental science. This review briefly describes the general feature of magnetosome-producing microorganisms. This article also highlights recent advances in the understanding of the biochemical and magnetic characteristics of bacterial magnetosome, as well as the magnetosome formation mechanism including iron ions uptake, magnetosome membrane formation, biomineralization and magnetosome chain assembly. Finally, this review presents the potential applications of bacterial magnetosome in biomedicine, wastewater treatment, and the significance of mineralization of magnetosome in biology and geology.

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We used conventional methods to investigate the mechanism by which Acidithiobacillus ferrooxidans colonizes a solid surface by assessing pili-mediated sliding, twitching motility, and adherence. A. ferrooxidans slided to form circular oxidized zones around each colony. This suggested that slide motility occurs through pili or flagella, though A. ferrooxidans strains ATCC 19859 and ATCC 23270 lack flagella. The results of reverse transcription-PCR demonstrated that the putative major pili gene of A. ferrooxidans strains ATCC 19859, ATCC 23270, and BY3 genes were transcribed. Culture of A. ferrooxidans between silicone gel and glass led to the production of type IV pili and the formation of rough twitching motility zones. When the bacteria were grown on lean ore cubes, pyrite was colonized readily by A. ferrooxidans and there is a correlation between pilus expression and strong attachment. However, non-pili bacteria attached minimally to the mineral surface. The results show a correlation between these functions and pilus expression.

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