Lecture-4 (general principles of biomineralization)

General Principles of Biomineralization‣ Information is available about the structures ofbiominerals‣ How they vary in different organisms‣ Little is known about the detailed molecularinteractions governing their construction‣ However, there are some “general principles”

Biologically induced biomineralization‣ OH - fluxes are involved with precipitation of oxides,carbonates and phosphates‣ H 2 S and electrons induce precipitation of sulfides andmixed-valence iron oxides‣ Some bacteria are able to accumulate and passivatetoxic metal ions, such as UO 22+, Pb 2+ , Cd 2+‣ Biologically induced biomineralization could have animportant role in clean up of polluted waters andsoils

Biologically induced biomineralization

Biologically induced biomineralizationEpicellular biomineralization

Epicellular biomineralization‣ Minerals form along the surface of the cell‣ They remain firmly attached to the cell wall‣ In some cases individual cells become totally encrustedin the mineral deposit. They increase in weight andsink to the bottom of the ocean forming sediments‣ Organic components (lipids, proteins, polysaccharides)of the cell wall are involved, by creating surfaces forprecipitation

Control and Morphology inEpicellular biomineralization‣ There is no strict cellular control‣ Size, shape, structure, composition and organization arepoorly defined and heterogenous20 nmIrregularly shaped Fe 3 O 4(magnetite) particlesProduced by a bacteriumCalled GS-15

Biologically Controlled biomineralization‣ Biologically controlled biomineralization is a highlyregulated process‣ It produces minerals such as bones, shells, and teeththat have specific biological functions and structures‣ These biominerals are identified by their species-specificcrystallochemical properties

Characteristics of these biominerals

Example: Magnetotactic Bacteria

Site-directedbiomineralization: : it occursAt specific sites‣ Epicellular(on the cell wall)‣ Intercellular(in the spaces between closely packed cells)‣ Intracellular(inside enclosed compartments within the cell)‣ Extracellular(on or within an insoluble macromolecularframework outside the cell)

Lipid VesiclesMineralization in small spaces

Macromolecular frameworks‣ Vesicles are not suitable for building large structuressuch as bones, shells or teeth‣ An organic matrix is needed‣ It is composed of insoluble proteins andpolysaccharides such as collagen or chitin‣ The mineral phase is deposited in close associationwith the organic matrixEarly stages of egshellFormation showing calciteCrystals and macromolecularfibers

Site RequirementsAlthough the mechanisms that govern the biological control ofBiomineralization vary enormously in different systems, there areFour basic requirements associated with mineralization sites, suchAs vesicles and macromolecuar frameworks‣ Spatial delineationFor size and shape control‣ Diffusion-limited ion flowFor controlling solution composition‣ Chemical regulationfor increasing ionic concentrations‣ Organic surfacesFor controlling nucleation

Control mechanisms: regulation of chemistry,space, structure, morphology, and construction

Chemical controlFour fundamental physicochemical factors‣ Solubility‣ Supersaturation‣ Nucleation‣ Crystal growthThese are chemically controlled in biomineralization bycoordinated ion transport and molecular-based inhibitorsand promoters

Spatial controlThe control of space in biomineralization occurs throughthe supramolecular pre-organization of organicmolecules, and impacts on the size and shape ofmineral deposits and the chemical mechanisms of theirdeposition

Structural controlNon-oriented mosaic Iso-orientedThe organic matrix acts as an organic templatefor inorganic nucleationInterfacial molecular recognition

Morphological control

‣ Vectorial regulationMorphological control‣ Mineral growth process is controlled by organicboundaries that change in size and shape withtime‣ The inorganic phase is progressively routed alongspecific directions set by a biological program‣ Patterning program… morphogenesis

Constructional control‣ Controlled construction of hierarchical structures‣ Assembly of mineral-based building blocks into aseries of progressively higher-order structures‣ In bone, tiny crystals of hydroxyapatite are interwovenwith collagen fibers‣ Biomineral tectonics

General model