Biomineralization

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Biomineralization, or biomineralisation is the process by which living organisms produce minerals, often to harden or stiffen existing tissues. Biomineralization_sentence_0

Such tissues are called mineralized tissues. Biomineralization_sentence_1

It is an extremely widespread phenomenon; all six taxonomic kingdoms contain members that are able to form minerals, and over 60 different minerals have been identified in organisms. Biomineralization_sentence_2

Examples include silicates in algae and diatoms, carbonates in invertebrates, and calcium phosphates and carbonates in vertebrates. Biomineralization_sentence_3

These minerals often form structural features such as sea shells and the bone in mammals and birds. Biomineralization_sentence_4

Organisms have been producing mineralised skeletons for the past 550 million years. Biomineralization_sentence_5

Ca carbonates and Ca phosphates are usually crystalline, but silica organisms (sponges, diatoms...) are always non crystalline minerals. Biomineralization_sentence_6

Other examples include copper, iron and gold deposits involving bacteria. Biomineralization_sentence_7

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). Biomineralization_sentence_8

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. Biomineralization_sentence_9

The structures of these biocomposite materials are highly controlled from the nanometer to the macroscopic level, resulting in complex architectures that provide multifunctional properties. Biomineralization_sentence_10

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. Biomineralization_sentence_11

Biological roles Biomineralization_section_0

Among metazoans, biominerals composed of calcium carbonate, calcium phosphate or silica perform a variety of roles such as support, defense and feeding. Biomineralization_sentence_12

It is less clear what purpose biominerals serve in bacteria. Biomineralization_sentence_13

One hypothesis is that cells create them to avoid entombment by their own metabolic byproducts. Biomineralization_sentence_14

Iron oxide particles may also enhance their metabolism. Biomineralization_sentence_15

Biology Biomineralization_section_1

If present on a super-cellular scale, biominerals are usually deposited by a dedicated organ, which is often defined very early in the embryological development. Biomineralization_sentence_16

This organ will contain an organic matrix that facilitates and directs the deposition of crystals. Biomineralization_sentence_17

The matrix may be collagen, as in deuterostomes, or based on chitin or other polysaccharides, as in molluscs. Biomineralization_sentence_18

Shell formation in molluscs Biomineralization_section_2

Further information: Mollusc shell Biomineralization_sentence_19

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. Biomineralization_sentence_20

Molluscan shells consist of 95–99% calcium carbonate by weight, while an organic component makes up the remaining 1–5%. Biomineralization_sentence_21

The resulting composite has a fracture toughness ≈3000 times greater than that of the crystals themselves. Biomineralization_sentence_22

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. Biomineralization_sentence_23

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. Biomineralization_sentence_24

The most described arrangement in mollusc shells is the nacre - prismatic shells, known in large shells as Pinna or the pearl oyster (Pinctada). Biomineralization_sentence_25

Not only the structure of the layers differ, but their mineralogy and chemical composition also differ. Biomineralization_sentence_26

Both contain organic components (proteins, sugars and lipids) and the organic components are characteristic of the layer, and of the species. Biomineralization_sentence_27

The structures and arrangements of mollusc shells are diverse, but they share some features: the main part of the shell is a crystalline Ca carbonate (aragonite, calcite), despite some amorphous Ca carbonate occurs; and despite they react as crystals, they never show angles and facets. Biomineralization_sentence_28

The examination of the inner structure of the prismatic units, nacreous tablets, foliated laths... shows irregular rounded granules. Biomineralization_sentence_29

Mineral production and degradation in fungi Biomineralization_section_3

Fungi are a diverse group of organisms that belong to the eukaryotic domain. Biomineralization_sentence_30

Studies of their significant roles in geological processes, "geomycology", has shown that fungi are involved with biomineralization, biodegradation, and metal-fungal interactions. Biomineralization_sentence_31

In studying fungi's roles in biomineralization, it has been found that fungi deposit minerals with the help of an organic matrix, such as a protein, that provides a nucleation site for the growth of biominerals. Biomineralization_sentence_32

Fungal growth may produce a copper-containing mineral precipitate, such as copper carbonate produced from a mixture of (NH4)2CO3 and CuCl2. Biomineralization_sentence_33

The production of the copper carbonate is produced in the presence of proteins made and secreted by the fungi. Biomineralization_sentence_34

These fungal proteins that are found extracellularly aid in the size and morphology of the carbonate minerals precipitated by the fungi. Biomineralization_sentence_35

In addition to precipitating carbonate minerals, fungi can also precipitate uranium-containing phosphate biominerals in the presence of organic phosphorus that acts a substrate for the process. Biomineralization_sentence_36

The fungi produce a hyphal matrix, also known as mycelium, that localizes and accumulates the uranium minerals that have been precipitated. Biomineralization_sentence_37

Although uranium is often deemed as toxic towards living organisms, certain fungi such as Aspergillus niger and Paecilomyces javanicus can tolerate it. Biomineralization_sentence_38

Though minerals can be produced by fungi, they can also be degraded; mainly by oxalic-acid producing strains of fungi. Biomineralization_sentence_39

Oxalic acid production is increased in the presence of glucose for three organic acid producing fungi – Aspergillus niger, Serpula himantioides, and Trametes versicolor. Biomineralization_sentence_40

These fungi have been found to corrode apatite and galena minerals. Biomineralization_sentence_41

Degradation of minerals by fungi is carried out through a process known as neogenesis. Biomineralization_sentence_42

The order of most to least oxalic acid secreted by the fungi studied are Aspergillus niger, followed by Serpula himantioides, and finally Trametes versicolor. Biomineralization_sentence_43

These capabilities of certain groups of fungi have a major impact on corrosion, a costly problem for many industries and the economy. Biomineralization_sentence_44

Chemistry Biomineralization_section_4

The majority of biominerals fall into three distinct mineral classes: carbonates, silicates and phosphates. Biomineralization_sentence_45

Carbonates Biomineralization_section_5

The major carbonates are CaCO3. Biomineralization_sentence_46

The most common polymorphs in biomineralization are (e.g. foraminifera, coccolithophores) and aragonite (e.g. corals), although metastable vaterite and amorphous calcium carbonate can also be important, either structurally or as intermediate phases in biomineralization. Biomineralization_sentence_47

Some biominerals include a mixture of these phases in distinct, organised structural components (e.g. bivalve shells). Biomineralization_sentence_48

Carbonates are particularly prevalent in marine environments, but also present in fresh water and terrestrial organisms. Biomineralization_sentence_49

Silicates Biomineralization_section_6

Silicates are particularly common in marine biominerals, where Diatoms and Radiolaria form frustules from hydrated amorphous silica (Opal). Biomineralization_sentence_50

Phosphates Biomineralization_section_7

The most common phosphate is hydroxyapatite, a calcium phosphate (Ca10(PO4)6(OH)2) which is a primary constituent of bone, teeth, and fish scales. Biomineralization_sentence_51

Other Minerals Biomineralization_section_8

Beyond these main three categories, there a number of less common types of biominerals, usually resulting from a need for specific physical properties or the organism inhabiting an unusual environment. Biomineralization_sentence_52

For example, teeth that are primarily used for scraping hard substrates may be reinforced with particularly tough minerals, such as the iron minerals Magnetite in Chiton, or Goethite in Limpets. Biomineralization_sentence_53

Gastropod molluscs living close to hydrothermal vents reinforce their carbonate shells with the iron-sulphur minerals pyrite and greigite. Biomineralization_sentence_54

Magnetotactic bacteria also employ magnetic iron minerals magnetite and greigite to produce magnetosomes to aid orientation and distribution in the sediments. Biomineralization_sentence_55

Planktic acantharea (radiolaria) form strontium sulphate (Celestine) spicules. Biomineralization_sentence_56

Evolution Biomineralization_section_9

The first evidence of biomineralization dates to some  million years ago, and sponge-grade organisms may have formed skeletons  million years ago. Biomineralization_sentence_57

But in most lineages, biomineralization first occurred in the Cambrian or Ordovician periods. Biomineralization_sentence_58

Organisms used whichever form of calcium carbonate was more stable in the water column at the point in time when they became biomineralized, and stuck with that form for the remainder of their biological history (but see for a more detailed analysis). Biomineralization_sentence_59

The stability is dependent on the Ca/Mg ratio of seawater, which is thought to be controlled primarily by the rate of sea floor spreading, although atmospheric CO 2 levels may also play a role. Biomineralization_sentence_60

Biomineralization evolved multiple times, independently, and most animal lineages first expressed biomineralized components in the Cambrian period. Biomineralization_sentence_61

Many of the same processes are used in unrelated lineages, which suggests that biomineralization machinery was assembled from pre-existing "off-the-shelf" components already used for other purposes in the organism. Biomineralization_sentence_62

Although the biomachinery facilitating biomineralization is complex – involving signalling transmitters, inhibitors, and transcription factors – many elements of this 'toolkit' are shared between phyla as diverse as corals, molluscs, and vertebrates. Biomineralization_sentence_63

The shared components tend to perform quite fundamental tasks, such as designating that cells will be used to create the minerals, whereas genes controlling more finely tuned aspects that occur later in the biomineralization process – such as the precise alignment and structure of the crystals produced – tend to be uniquely evolved in different lineages. Biomineralization_sentence_64

This suggests that Precambrian organisms were employing the same elements, albeit for a different purpose — perhaps to avoid the inadvertent precipitation of calcium carbonate from the supersaturated Proterozoic oceans. Biomineralization_sentence_65

Forms of mucus that are involved in inducing mineralization in most metazoan lineages appear to have performed such an anticalcifatory function in the ancestral state. Biomineralization_sentence_66

Further, certain proteins that would originally have been involved in maintaining calcium concentrations within cells are homologous to all metazoans, and appear to have been co-opted into biomineralization after the divergence of the metazoan lineages. Biomineralization_sentence_67

The galaxins are one probable example of a gene being co-opted from a different ancestral purpose into controlling biomineralization, in this case being 'switched' to this purpose in the Triassic scleractinian corals; the role performed appears to be functionally identical to the unrelated pearlin gene in molluscs. Biomineralization_sentence_68

Carbonic anhydrase serves a role in mineralization in sponges, as well as metazoans, implying an ancestral role. Biomineralization_sentence_69

Far from being a rare trait that evolved a few times and remained stagnant, biomineralization pathways in fact evolved many times and are still evolving rapidly today; even within a single genus it is possible to detect great variation within a single gene family. Biomineralization_sentence_70

The homology of biomineralization pathways is underlined by a remarkable experiment whereby the nacreous layer of a molluscan shell was implanted into a human tooth, and rather than experiencing an immune response, the molluscan nacre was incorporated into the host bone matrix. Biomineralization_sentence_71

This points to the exaptation of an original biomineralization pathway. Biomineralization_sentence_72

The most ancient example of biomineralization, dating back 2 billion years, is the deposition of magnetite, which is observed in some bacteria, as well as the teeth of chitons and the brains of vertebrates; it is possible that this pathway, which performed a magnetosensory role in the common ancestor of all bilaterians, was duplicated and modified in the Cambrian to form the basis for calcium-based biomineralization pathways. Biomineralization_sentence_73

Iron is stored in close proximity to magnetite-coated chiton teeth, so that the teeth can be renewed as they wear. Biomineralization_sentence_74

Not only is there a marked similarity between the magnetite deposition process and enamel deposition in vertebrates but some vertebrates even have comparable iron storage facilities near their teeth. Biomineralization_sentence_75

Biomineralization_table_general_0

Type of mineralizationBiomineralization_header_cell_0_0_0 Examples of organismsBiomineralization_header_cell_0_0_1
Calcium carbonate ( or aragonite)Biomineralization_cell_0_1_0 Biomineralization_cell_0_1_1
SilicaBiomineralization_cell_0_2_0 Biomineralization_cell_0_2_1
Apatite (phosphate carbonate)Biomineralization_cell_0_3_0 Biomineralization_cell_0_3_1

Astrobiology Biomineralization_section_10

It has been suggested that biominerals could be important indicators of extraterrestrial life and thus could play an important role in the search for past or present life on Mars. Biomineralization_sentence_76

Furthermore, organic components (biosignatures) that are often associated with biominerals are believed to play crucial roles in both pre-biotic and biotic reactions. Biomineralization_sentence_77

On January 24, 2014, NASA reported that current studies by the Curiosity and Opportunity rovers on the planet Mars will now be searching for evidence of ancient life, including a biosphere based on autotrophic, chemotrophic and/or chemolithoautotrophic microorganisms, as well as ancient water, including fluvio-lacustrine environments (plains related to ancient rivers or lakes) that may have been habitable. Biomineralization_sentence_78

The search for evidence of habitability, taphonomy (related to fossils), and organic carbon on the planet Mars is now a primary NASA objective. Biomineralization_sentence_79

Potential applications Biomineralization_section_11

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. Biomineralization_sentence_80

Furthermore, the quantities produced are small, and the resultant material is usually irreproducible because of the difficulties in controlling agglomeration. Biomineralization_sentence_81

In contrast, materials produced by organisms have properties that usually surpass those of analogous synthetically manufactured materials with similar phase composition. Biomineralization_sentence_82

Biological materials are assembled in aqueous environments under mild conditions by using macromolecules. Biomineralization_sentence_83

Organic macromolecules collect and transport raw materials and assemble these substrates and into short- and long-range ordered composites with consistency and uniformity. Biomineralization_sentence_84

The aim of biomimetics is to mimic the natural way of producing minerals such as apatites. Biomineralization_sentence_85

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. Biomineralization_sentence_86

Often, the mineral phases are not pure but are made as composites that entail an organic part, often protein, which takes part in and controls the biomineralisation. Biomineralization_sentence_87

These composites are often not only as hard as the pure mineral but also tougher, as the micro-environment controls biomineralisation. Biomineralization_sentence_88

Uranium contaminants in groundwater Biomineralization_section_12

Biomineralization may be used to remediate groundwater contaminated with uranium. Biomineralization_sentence_89

The biomineralization of uranium primarily involves the precipitation of uranium phosphate minerals associated with the release of phosphate by microorganisms. Biomineralization_sentence_90

Negatively charged ligands at the surface of the cells attract the positively charged uranyl ion (UO2). Biomineralization_sentence_91

If the concentrations of phosphate and UO2 are sufficiently high, minerals such as autunite (Ca(UO2)2(PO4)2 10-12H2O) or polycrystalline HUO2PO4 may form thus reducing the mobility of UO2. Biomineralization_sentence_92

Compared to the direct addition of inorganic phosphate to contaminated groundwater, biomineralization has the advantage that the ligands produced by microbes will target uranium compounds more specifically rather than react actively with all aqueous metals. Biomineralization_sentence_93

Stimulating bacterial phosphatase activity to liberate phosphate under controlled conditions limits the rate of bacterial hydrolysis of organophosphate and the release of phosphate to the system, thus avoiding clogging of the injection location with metal phosphate minerals. Biomineralization_sentence_94

The high concentration of ligands near the cell surface also provides nucleation foci for precipitation, which leads to higher efficiency than chemical precipitation. Biomineralization_sentence_95

List of minerals Biomineralization_section_13

Examples of biogenic minerals include: Biomineralization_sentence_96

Biomineralization_unordered_list_0

See also Biomineralization_section_14

Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Biomineralization.