Biomineralisation is the process by which living organisms produce minerals, often to harden or stiffen existing tissues. It is an extremely widespread phenomenon; all five taxonomic kingdoms contain members that are able to form minerals, and over 60 different minerals have been identified in organisms.^[1][2] Examples include silicates in algae and diatoms, carbonates in invertebrates, and calcium phosphates and carbonates in vertebrates. These minerals often form structural features such as sea shells and the bone in mammals and birds. Organisms have been producing mineralised skeletons for the past 550 million years. Other examples include copper, iron and gold deposits involving bacteria. Biologically-formed minerals often have special uses such as magnetic sensors in magnetotactic bacteria (Fe₃O₄), gravity sensing devices (CaCO₃, CaSO₄, BaSO₄) and iron storage and mobilization (Fe₂O₃•H₂O in the protein ferritin).

In terms of taxonomic distribution, the most common biominerals are the phosphate and carbonate salts of calcium that are used in conjunction with organic polymers such as collagen and chitin to give structural support to bones and shells. The structures of these biocomposite materials are highly controlled from the nanometer to the macroscopic level, resulting in complex architectures that provide multifunctional properties. Because this range of control over mineral growth is desirable for materials engineering applications, there is significant interest in understanding and elucidating the mechanisms of biologically controlled biomineralization.^[3][4]

Contents 1 Potential applications 1.1 Astrobiology 2 Evolution 3 Shell formation in molluscs 4 See also 5 References 5.1 Footnotes 5.2 Key reference 5.3 Additional sources 6 External links

[edit] Potential applications

Most traditional approaches to synthesis of nanoscale materials are energy inefficient, requiring stringent conditions (e.g., high temperature, pressure or pH) and often produce toxic byproducts. Furthermore, the quantities produced are small, and the resultant material is usually irreproducible because of the difficulties in controlling agglomeration.^[5] In contrast, materials produced by organisms have properties that usually surpass those of analogous synthetically manufactured materials with similar phase composition. Biological materials are assembled in aqueous environments under mild conditions by using macromolecules. Organic macromolecules collect and transport raw materials and assemble these substrates and into short- and long-range ordered composites with consistency and uniformity. The aim of biomimetics is to mimic the natural way of producing minerals such as apatites. Many man-made crystals require elevated temperatures and strong chemical solutions whereas the organisms have long been able to lay down elaborate mineral structures at ambient temperatures. Often the mineral phases are not pure but are made as composites which entail an organic part, often protein, which takes part in and controls the biomineralisation. These composites are often not only as hard as the pure mineral but also tougher, as at last, the micro-environment controls biomineralisation.

[edit] Astrobiology

It has been suggested that biominerals could be important indicators of estraterrestrial life and thus could play an important role in the search for past or present life on Mars. Furthermore, organic components (biosignatures) that are often associated with biominerals are believed to play crucial roles in both pre-biotic and biotic reactions.^[6]

[edit] Evolution

In most lineages, biomineralisation first occurred in the Cambrian or Ordovician periods. Organisms used whichever form of calcium carbonate was more stable in the water column at the point in time when they became biomineralised, and stuck with that form for the remainder of their biological history.^[7]

[edit] Shell formation in molluscs

The mollusc shell is a biogenic composite material that has been the subject of much interest in materials science because of its unusual properties and its model character for biomineralization. Molluscan shells consist of 95-99% calcium carbonate by weight, while an organic component makes up the remaining 1-5%. The resulting composite has a fracture toughness ~3000 times greater than that of the crystals themselves.^[8] In the biomineralization of the mollusc shell, specialized proteins are responsible for directing crystal nucleation, phase, morphology, and growths dynamics and ultimately give the shell its remarkable mechanical strength. The application of biomimetic principles elucidated from mollusc shell assembly and structure may help in fabricating new composite materials with enhanced optical, electronic, or structural properties.

[edit] See also

• Diatomaceous earth
• Magnetotactic bacteria
• Biocrystallization
• Biointerface

[edit] References

[edit] Footnotes

[edit] Key reference

• Lowenstam, H. A. (13 Mar 1981). "Minerals Formed by Organisms". Science 211 (4487). doi:10.2307/1685216. ISSN 00368075.  edit

[edit] Additional sources

• Addadi, L. and S. Weiner (1992). "Control And Design Principles In Biological Mineralization" (abstract). Angewandte Chemie International Edition in English 31 (2): 153–169. doi:10.1002/anie.199201531. http://www3.interscience.wiley.com/cgi-bin/abstract/106587877/ABSTRACT?CRETRY=1&SRETRY=0. 
• Boskey, A.L. (2003). "Biomineralization: An overview". Connective Tissue Research 44 (Supplement 1): 5–9. doi:10.1080/713713622.  PMID 12952166
• McPhee, Joseph (2006). "The Little Workers of the Mining Industry". Science Creative Quarterly (2). http://www.scq.ubc.ca/?p=342. Retrieved 2006-11-03. 
• Schmittner, Karl-Erich and Giresse, Pierre (1999). "Micro-environmental controls on biomineralization: superficial processes of apatite and calcite precipitation in Quaternary soils, Roussillon, France". Sedimentology 46 (3): 463–476. doi:10.1046/j.1365-3091.1999.00224.x. 
• Weiner, S. and L. Addadi (1997). "Design strategies in mineralized biological materials". Journal of Materials Chemistry 7 (5): 689–702. doi:10.1039/a604512j. http://www.rsc.org/Publishing/Journals/JM/article.asp?doi=a604512j. Retrieved 2006-11-03. 
• Dauphin, Y. (2005). "Biomineralization". Encyclopedia of Inorganic Chemistry (R.B. King ed)., Wiley & Sons 1: 391–404. 
• Cuif, J.P. and Sorauf, J.E. (2001). "Biomineralization and diagenesis in the Scleractinia : part I, biomineralization". Bull. Tohoku Univ. Museum, 1: 144–151. 
• Dauphin, Y. (2002). "Structures, organo mineral compositions and diagenetic changes in biominerals". Current Opinion in Colloid & Interface Science 7: 133–138. doi:10.1016/S1359-0294(02)00013-4. 

[edit] External links

• An overview of the bacteria involved in biomineralization from the Science Creative Quarterly
• [1] http://biomin.geol.u-psud.fr
• [2] http://biocalc.geol.u-psud.fr