Question

consists of a nano-sized crystal of a magnetic iron mineral which is enveloped by a lipid bilayer membrane.

Answer 1

Ecology, Diversity, and Evolution of Magnetotactic Bacteria

Christopher T. Lefèvre and Dennis A. Bazylinski

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ABSTRACT

SUMMARY

Magnetotactic bacteria (MTB) are widespread, motile, diverse prokaryotes that biomineralize a unique organelle called the magnetosome. Magnetosomes consist of a nano-sized crystal of a magnetic iron mineral that is enveloped by a lipid bilayer membrane. In cells of almost all MTB, magnetosomes are organized as a well-ordered chain. The magnetosome chain causes the cell to behave like a motile, miniature compass needle where the cell aligns and swims parallel to magnetic field lines. MTB are found in almost all types of aquatic environments, where they can account for an important part of the bacterial biomass. The genes responsible for magnetosome biomineralization are organized as clusters in the genomes of MTB, in some as a magnetosome genomic island. The functions of a number of magnetosome genes and their associated proteins in magnetosome synthesis and construction of the magnetosome chain have now been elucidated. The origin of magnetotaxis appears to be monophyletic; that is, it developed in a common ancestor to all MTB, although horizontal gene transfer of magnetosome genes also appears to play a role in their distribution. The purpose of this review, based on recent progress in this field, is focused on the diversity and the ecology of the MTB and also the evolution and transfer of the molecular determinants involved in magnetosome formation.

INTRODUCTION

Magnetotactic bacteria (MTB) are aquatic prokaryotes whose direction of motility is directed by the Earth's geomagnetic and externally applied magnetic fields (1). These ubiquitous microorganisms represent a morphologically, phylogenetically, and physiologically diverse group of Gram-negative bacteria that biomineralize unique organelles called magnetosomes, which are responsible for the cells' magnetotactic behavior, which is referred to as magnetotaxis (2). Magnetosomes consist of magnetic mineral crystals, either magnetite (Fe3O4) or greigite (Fe3S4), enveloped by a bilayer membrane composed mostly of phospholipids, called the magnetosome membrane, that contains a number of proteins not present in the cytoplasmic and outer membranes (OMs) and are unique to MTB (3, 4). Although magnetosome magnetite and greigite crystals can have different morphologies, mature crystals of both minerals generally lie within the single-magnetic-domain size range, about 35 to 120 nm, in which they have the highest possible magnetic moment per unit volume