Mineral formation extracellular deposition

Figure 10.34 shows SEM images of the samples cultured for 5 days, demonstrating the cell proliferation and early stage cell differentiation [179]. On spinel surfaces, cells formed a confluent layer covering the entire surface, as shown in Fig. 10.34a, b. Cells were observed to adhere to each other with cellular microextensions and connected to substrate in addition to the neighboring cells, as demonstrated in Fig. 10.34b. On AlON surfaces, cell growth was observed to be less pronounced. From a low-magnification SEM image, as shown in Fig. 10.34c, it was observed that cells were stiU in the process of confluent layer formation on AlON , which was unlike spinel surface shown in Fig. 10.34b, where cells had already started to mineralize their extracellular matrix with the abundance deposition of apatite minerals [180, 181].

It will be apparent that if normal extracellular fluids were subjected to an isotonic resorption of sodium and chloride ions by the process, the net effect would be to concentrate other ions and precipitate minerals. This suggestion was made613 to explain one of the methods of forming deposits in the calciferious glands of earthworms. It was proposed that the posterior glands received blood directly from the intestine. Fluid was formed in these glands by a process of filtration and saline was then resorbed by the epithelial cells. This resulted in the formation of calcareous deposits (Fig. 5). 

Bone sialoprotein, osteopontin, and osteocalcin are synthesized and deposited as the mineralization process begins and mineral nodules form (Stein and Lian, 1993). Bone sialoprotein contains the cell-adhesive arginine-glycine-aspartic acid peptide sequence and may thus mediate osteoblast adhesion on the extracellular matrix (Gehron-Robey, 1989). Osteocalcin, a calcium-binding protein, interacts with hydroxyapatite and is thought to mediate coupling of bone resorption (by osteoclasts) and bone formation (by osteoblasts and/or osteocytes) (Stein and Lian, 1993). 

Fig. 2.3.4. Pathways of ions across cells in the formation of CaC03. (a) Ion movement through a cell to an extracellular space where mineral deposition occurs (large area marked diagonally), (b) Ion movement through intercellular space, (c) Ion movement into an intracellular vesicle where mineral deposition occurs (smaller circle with diagonal markings).

Layer-silicates Recent studies have also demonstrated the potential microbial influence on clay mineral (layer silicates) formation at hydrothermal vents. Bacterial cells covered (or completely replaced) with a Fe-rich silicate mineral (putative nontronite), in some cases oriented in extracellular polymers (as revealed by TEM analysis), were found in deep-sea sediments of Iheya Basin, Okinawa Trough (Ueshima Tazaki, 2001), and in soft sediments, and on mineral surfaces in low-temperature (2-50°C) waters near vents at Southern Explorer Ridge in the northeast Pacific (Fortin etal., 1998 Fig. 8.6). The Fe-silicate is believed to form as a result of the binding and concentration of soluble Si and Fe species to reactive sites (e.g. carboxyl, phosphoryl) on EPS (Ueshima Tazaki, 2001). Formation of Fe-silicate may also involve complex binding mechanisms, whereas metal ions such as Fe possibly bridge reactive sites within cell walls to silicate anions to initiate silicate nucleation (Fortin etal., 1998). Alt (1988) also reported the presence of nontronite associated with Mn- and Fe-oxide-rich deposits from seamounts on the EPR. The presence of bacteria-like filaments within one nontronite sample was taken to indicate that bacterial activity may have been associated with nontronite formation. Although the formation of clay minerals at deep-sea hydrothermal vents has not received much attention, it seems probable that based on these studies, biomineralisation of clay minerals is ubiquitous in these environments. 

Biofilm formation. In industrial systems, direct and indirect biomineralization processes can influence scale formation and mineral deposition within the biofilm. Clay particles and other debris become trapped in the extracellular slime, adding to the thickness and heterogeneity of the biofilm. Iron, manganese, and silica are often elevated in biofilms as a result of mineral deposition and ion exchange. In the case of iron-oxidizing bacteria found in aerobic water systems, metal oxides are an important component of the biofilm. In steel systems operating under anaerobic conditions, iron sulfides can be deposited when ferrous ions released by corrosion of steel surfaces precipitate with sulfide generated by bacteria in the biofilm. ... 

Calcium ions are fixed into the biofilm by the attraction of carboxy-late functional groups on the polysaccharides. In fact, divalent cations, such as calcium and magnesium, are integral in the formation of gels in some extracellular polysaccharides. A familiar biofilm-induced mineral deposit is the calcium phosphate scale that the dental hygienist removes from teeth. When biofilms grow on tooth surfaces, they are referred to as plaques. If these plaques are not continually removed, they will accumulate calcium salts, mainly calcium phosphate, and form tartar (scale). 

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