Magnetotactic bacteria

About: Magnetotactic bacteria is a research topic. Over the lifetime, 1118 publications have been published within this topic receiving 43741 citations.

Chains of magnetosomes extracted from AMB-1 magnetotactic bacteria for application in alternative magnetic field cancer therapy.

Abstract: Chains of magnetosomes extracted from AMB-1 magnetotactic bacteria are shown to be highly efficient for cancer therapy when they are exposed to an alternative magnetic field. When a suspension containing MDA-MB-231 breast cancer cells was incubated in the presence of various amounts of extracted chains of magnetosomes, the viability of these cells remained high in the absence of an alternative magnetic field. By contrast, when this suspension was exposed to an alternative magnetic field of frequency 183 kHz and field strengths of 20, 40, or 60 mT, up to 100% of these cells were destroyed. The antitumoral activity of the extracted chains of magnetosomes is demonstrated further by showing that they can be used to fully eradicate a tumor xenografted under the skin of a mouse. For that, a suspension containing ∼1 mg of extracted chains of magnetosomes was administered within the tumor and the mouse was exposed to three heat cycles of 20 min, during which the tumor temperature was raised to ∼43 °C. We also dem...

A large gene cluster encoding several magnetosome proteins is conserved in different species of magnetotactic bacteria.

Abstract: In magnetotactic bacteria, a number of specific proteins are associated with the magnetosome membrane (MM) and may have a crucial role in magnetite biomineralization. We have cloned and sequenced the genes of several of these polypeptides in the magnetotactic bacterium Magnetospirillum gryphiswaldense that could be assigned to two different genomic regions. Except for mamA, none of these genes have been previously reported to be related to magnetosome formation. Homologous genes were found in the genome sequences of M. magnetotacticum and magnetic coccus strain MC-1. The MM proteins identified display homology to tetratricopeptide repeat proteins (MamA), cation diffusion facilitators (MamB), and HtrA-like serine proteases (MamE) or bear no similarity to known proteins (MamC and MamD). A major gene cluster containing several magnetosome genes (including mamA and mamB) was found to be conserved in all three of the strains investigated. The mamAB cluster also contains additional genes that have no known homologs in any nonmagnetic organism, suggesting a specific role in magnetosome formation.

Anaerobic magnetite production by a marine, magnetotactic bacterium

Abstract: Bacterial production of magnetite represents a significant contribution to the natural remanent magnetism of deep-sea and other sediments1–5. Because cells of the freshwater magnetotactic bacterium Aquaspirillum magnetotacticum require molecular oxygen for growth and magnetite synthesis6, production of magnetite by magnetotactic bacteria has been considered to occur only in surficial aerobic sediments7. Moreover, it has been suggested that deposits of single-domain magnetite crystals are palaeooxygen indicators presumably having been formed under predominantly microaerobic conditions5–8. In contrast, some nonmagnetotactic, dissimilatory iron-reducing bacteria, such as the recently described strain GS-15 by Lovley et al.7, synthesize extracellular magnetite from hydrous ferric oxide under anaerobic conditions. We now report the first isolation and axenic culture of a marine, magnetotactic bacterium, designated MV-1, that can synthesize intracellular, single-domain magnetite crystals under strictly anaerobic conditions. We conclude that magnetotactic bacteria do not necessarily require molecular oxygen for magnetite synthesis and suggest that they, as well as dissimilatory iron-reducing bacteria, can contribute to the natural remanent magnetism of even long-term anaerobic sediments.

Controlled Biomineralization of Magnetite (Fe(inf3)O(inf4)) and Greigite (Fe(inf3)S(inf4)) in a Magnetotactic Bacterium.

Abstract: A slowly moving, rod-shaped magnetotactic bacterium was found in relatively large numbers at and below the oxic-anoxic transition zone of a semianaerobic estuarine basin. Unlike all magnetotactic bacteria described to date, cells of this organism produce single-magnetic-domain particles of an iron oxide, magnetite (Fe(inf3)O(inf4)), and an iron sulfide, greigite (Fe(inf3)S(inf4)), within their magnetosomes. The crystals had different morphologies, being arrowhead or tooth shaped for the magnetite particles and roughly rectangular for the greigite particles, and were coorganized within the same chain(s) in the same cell with their long axes along the chain direction. Because the two crystal types have different crystallochemical characteristics, the findings presented here suggest that the formation of the crystal types is controlled by separate biomineralization processes and that the assembly of the magnetosome chain is controlled by a third ultrastructural process. In addition, our results show that in some magnetotactic bacteria, external environmental conditions such as redox and/or oxygen or hydrogen sulfide concentrations may affect the composition of the nonmetal part of the magnetosome mineral phase.