As stated in an Chapter 4, prokaryotes of both Domains or Superkingdoms, the Bacteria and the Archaea, mediate the formation of a large number of diverse minerals. They are known to do this either through biologically induced mineralization (BIM) (Lowenstam 1981) (the subject of Chapter 4 in this volume; Frankel and Bazylinski 2003) or biologically controlled mineralization (BCM). The latter has also been referred to as organic matrix-mediated mineralization (Lowenstam 1981) and boundary-organized biomineralization (Mann 1986). There are several important differences between BIM and BCM that will be discussed in detail in this chapter, most notably those dealing with aspects of the mineral crystals and the biomineralization process (see also Weiner and Dove 2003). However, there is another significant difference between the two modes of biomineralization and this is the aspect of functionality. Generally, in BIM there is no function to the biomineralized particles except, perhaps, as a solid substrate for attachment in the case of bacteria or as a form of protection against certain environmental conditions or attack from predators. However, it is easier to recognize the primary function of bone or shells produced by molluscs; two well-characterized examples of BCM by higher organisms. Functionality should always be examined when dealing with examples of biomineralization particularly in situations where the mineral product displays some qualities of both BIM and BCM.

In BCM, the organism exerts a great degree of crystallochemical control over the nucleation and growth of the mineral particles. For the most part, the minerals are directly synthesized at a specific location within or on the cell and only under certain conditions. The mineral particles produced by bacteria in BCM are characterized as well-ordered crystals with narrow size distributions, and specific, consistent particle morphologies. Because of these features, BCM processes are likely to be under specific chemical/biochemical and …

Biologically Controlled Mineralization in Prokaryotes

http://magneticliquid.narod.ru/autority/578.pdf

Diversity and vertical distribution of magnetotactic bacteria along chemical gradients in freshwater microcosms.

We characterized a population of bilophotrichously flagellated freshwater magnetotactic cocci (MC), referred to as ARB-1, morphologically, chemically, and phylogenetically. Cells examined using light microscopy, fluorescence microscopy, environmental scanning electron microscopy (ESEM), and transmission electron microscopy (TEM) contained three types of intracellular inclusions placed in a specific arrangement within the cell. Elemental compositions of the inclusions were determined using energy dispersive X-ray spectroscopy (EDS) from both ESEM and TEM. The spherical to ovoid cells contained two large phosphorus-rich inclusions that occupied most of the cell volume and appeared to be enclosed in a membrane or coating. Several smaller sulfur-rich inclusions were located at the end of the cell opposite the flagellar bundles. The magnetosomes, arranged either as a cluster, a chain, or a combination of both, were located proximal to the two flagellar bundles. Magnetite was identified as the mineral phase of ...

Organization and Elemental Analysis of P-, S-, and Fe-rich Inclusions in a Population of Freshwater Magnetococci

Magnetite-producing magnetotactic bacteria collected from the oxic–anoxic transition zone of chemically stratified marine environments characterized by O2/H2S inverse double gradients, contained internal S-rich inclusions resembling elemental S globules, suggesting they oxidize reduced S compounds that could support autotrophy. Two strains of marine magnetotactic bacteria, MV-1 and MV-2, isolated from such sites grew in O2-gradient media with H2S or thiosulfate (S2O32−) as electron sources and O2 as electron acceptor or anaerobically with S2O32− and N2O as electron acceptor, with bicarbonate (HCO3−)/CO2 as sole C source. Cells grown with H2S contained S-rich inclusions. Cells oxidized S2O32− to sulfate (SO42−). Both strains grew microaerobically with formate. Neither grew microaerobically with tetrathionate (S4O62−), methanol, or Fe2+ as FeS, or siderite (FeCO3). Growth with S2O32− and radiolabeled 14C-HCO3− showed that cell C was derived from HCO3−/CO2. Cell-free extracts showed ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO) activity. Southern blot analyses indicated the presence of a form II RubisCO (cbbM) but no form I (cbbL) in both strains. cbbM and cbbQ, a putative post-translational activator of RubisCO, were identified in MV-1. MV-1 and MV-2 are thus chemolithoautotrophs that use the Calvin–Benson–Bassham pathway. cbbM was also identified in Magnetospirillum magnetotacticum. Thus, magnetotactic bacteria at the oxic–anoxic transition zone of chemically stratified aquatic environments are important in C cycling and primary productivity.

Chemolithoautotrophy in the marine, magnetotactic bacterial strains MV-1 and MV-2.

This chapter examines and reviews features of biologically induced mineralization (BIM)- and biologically controlled mineralization (BCM)-type magnetic particles. It describes microorganisms that produce magnetic minerals (focusing mainly on the magnetotactic bacteria) and also describes the biomineralization processes involved in the synthesis of magnetic minerals. The chapter also reviews the physics and function of magnetotaxis in light of recent findings. In the microbial world, the most widely recognized example of BCM is magnetosome production by the magnetotactic bacteria. Although all freshwater magnetotactic bacteria synthesize magnetite as the mineral phase of their magnetsomes, many marine, estuarine, and salt marsh species produce an iron sulfide-type magnetosome which consists primarily of the magnetic iron sulfide greigite. The chapter discusses stoichiometry changes and specifically whether iron can be replaced with other transition metal ions and whether sulfur and oxygen can replace each other as the nonmetal component in the magnetosome mineral phase. The fact that many higher creatures biomineralize single-magnetic-domain magnetite crystals of similar morphologies suggests the intriguing idea that all these organisms have the same or a similar set of genes responsible for magnetite biomineralization that would probably have originated in the magnetotactic bacteria. Thus, studying how magnetotactic bacteria biomineralize magnetite might have a scientific impact far beyond the studies of microbiology and geology.

/pdf/biologically-controlled-mineralization-of-magnetic-iron-2cynbyqwxb.pdf

Iida Akihiko

Papers

Crystalline sulfur inclusions in magnetotactic bacteria