Inorganic Particles Produced by Microorganisms
- PDF / 217,551 Bytes
- 3 Pages / 420.48 x 639 pts Page_size
- 90 Downloads / 223 Views
INORGANIC
PARTICLES
PRODUCED
RICHARD B. FRANKEL Department of Physics, California Polytechnic State San Luis Obispo, CA 93407
BY
MICROORGANISMS
University,
ABSTRACT The processes by which microorganisms, particularly bacteria, produce inorganic mineral particles are reviewed. INTRODUCTION Biomineralization processes by which organisms form inorganic minerals are broadly distributed and occur in almost every phylum of the biological world [1-5]. There is a large diversity of minerals formed, with over 60 currently known [1]. Microorganisms, including eukaryotes (fungi, protozoa and algae) and prokaryotes (bacteria), are deeply involved in the geochemical cycling of inorganic elements via mineral formation and diagenesis. Biomineralization products include calcium carbonates, calcium phosphates, silica, iron oxides,, manganese oxides, iron phosphates, iron sulfides, and other heavy metal sulfides. The potency of bacteria in biomineralization is due to their high surface to volume ratio and to the negatively charged moieties that constitute their cell walls and are potential sites for the binding of cations [6]. BIOMINERALIZATION Lowenstam [7] has distinguished two general modes of biomineraliztion, namely, biologically-induced mineralization (BIM) and biologically controlled mineralization (BCM) (also referred to as boundary-organized biomineralization (BOB) [8]). In a BIM process, cellular export of metabolic products results in extracellular mineral formation with ions in the environment. The particles are essentially indistinguihable from those produced by purely inorganic processes. In a BCM process, the mineral phase is deposited in or on preformed organic vesicles or matrices produced by the organism. BIM processes are not controlled by the organism and the mineral particles typically have a large size distribution and no unique morphology. BCM processes involve highly controlled mineralization and the particles often have a narrow size distribution and species-specific morphology. Much of the current research on biomineralization phenomena is directed at elucidating the structure of the organic macromolecules involved in the BCM processes and the nature of the organic-inorganic interactions. In a very general way, all iron oxidation by molecular oxygen on the surface of the earth occurs by a BIM process because molecular oxygen in the atmosphere is a byproduct of photosynthesis. However, the distinction between BIM and BCM processes is more useful in considering more restricted situations, such as instances of iron biomineralization by bacteria.
Mat. Res. Soc. Symp. Proc. Vol. 218. @1991 Materials Research Society
78
Magnetite (Fe 3 0 4 ) formation by bacteria occurs by both BIM and BCM processes, in dissimilatory iron-reducing bacteria and magnetotactic bacteria, respectively. The dissimilatory ironreducing bacteria [9] respire Fe 3 + obtained from ferric oxyhydroxide in the environment, that is, they use ferric ions as terminal electron acceptors in their metabolism. The resulting ferrous ions are
Data Loading...
