This emerging construction biotechnology that uses microorganisms to extend
the durability of concrete structures relies on one of nature’s intriguing phenomena,
biomineralization.
2 Biomineralization
The use of biological agents in sealing concrete cracks seems to be one of the recent
alternative methods of combating concrete degradation. This approach is based on
biomineralization, a biochemical process in which organisms stimulate the formation of minerals [22]. The process is broadly classified into two groups: biologically
controlled mineralization (BCM) and biologically induced mineralization (BIM)
[23–25]. In BCM process, cell-associated minerals are synthesized within specific
conditions. It happens when cations interact with macromolecules such as lipids,
proteins, polysaccharides, etc. that initiate mineral crystal growth. On the other hand,
in BIM process, the minerals generally form by nucleation and grow extracellularly
through chemical reactions involving metabolic byproducts. Cell walls or exopolymers of bacteria such as slimes, sheaths, biofilms, etc. can serve as mineral
nucleation and growth sites [26–28]. One of the most interesting features of biomineralization is its ability of making minerals in highly remarkable precision and
reproducibility that are very difficult to achieve under the conventional synthetic
process. A classic example could be the bio-fabrication of biosilica glass, which
organisms such as diatoms, sponges, radiolarians, choanoflagellates, and plants form
in an astonishing variety that cannot be achieved by means of the existing chemical
methods [29]. The traditional synthetic process of nanoscale materials is known to be
energy intensive, involve stringent synthetic conditions (like high temperature,
pressure, or pH), and often release toxic by-products [30]. Moreover, not only the
quantities produced are small but also usually irreproducible due to the difficulties of
controlling agglomeration [31]. On the other hand, biologically synthesized materials often have properties that surpass the properties of the analogous products made
by the synthetic route [32]. Unlike the traditional chemical synthetic process,
biomineralization happens under mild conditions with the help of macromolecules
such as proteins [33]. Thus, biominerals are usually composites in nature due to the
presence of organic molecules; however, these materials are often not only as hard as
the pure mineral but are also tougher [32].
Different organisms are known to be involved in mineral formation. In higher
organisms, biomineralization involves production of cystolith inclusions in leaves
and strong body parts like bones, teeth, and shells. Currently, there are over
60 different mineral groups that are formed by organisms [34, 35] and deposited
in their body for various biological functions. Algal and diatoms silicates, invertebrate carbonates, and vertebrate calcium phosphates and carbonates can be mentioned as examples. As in the case of higher organisms, lower group of organisms,
especially prokaryotes such as bacteria, are highly potent agents of biomineralization. These organisms form an enormous variety of minerals such as carbonates,
298
G. Mamo and B. Mattiasson
the durability of concrete structures relies on one of nature’s intriguing phenomena,
biomineralization.
2 Biomineralization
The use of biological agents in sealing concrete cracks seems to be one of the recent
alternative methods of combating concrete degradation. This approach is based on
biomineralization, a biochemical process in which organisms stimulate the formation of minerals [22]. The process is broadly classified into two groups: biologically
controlled mineralization (BCM) and biologically induced mineralization (BIM)
[23–25]. In BCM process, cell-associated minerals are synthesized within specific
conditions. It happens when cations interact with macromolecules such as lipids,
proteins, polysaccharides, etc. that initiate mineral crystal growth. On the other hand,
in BIM process, the minerals generally form by nucleation and grow extracellularly
through chemical reactions involving metabolic byproducts. Cell walls or exopolymers of bacteria such as slimes, sheaths, biofilms, etc. can serve as mineral
nucleation and growth sites [26–28]. One of the most interesting features of biomineralization is its ability of making minerals in highly remarkable precision and
reproducibility that are very difficult to achieve under the conventional synthetic
process. A classic example could be the bio-fabrication of biosilica glass, which
organisms such as diatoms, sponges, radiolarians, choanoflagellates, and plants form
in an astonishing variety that cannot be achieved by means of the existing chemical
methods [29]. The traditional synthetic process of nanoscale materials is known to be
energy intensive, involve stringent synthetic conditions (like high temperature,
pressure, or pH), and often release toxic by-products [30]. Moreover, not only the
quantities produced are small but also usually irreproducible due to the difficulties of
controlling agglomeration [31]. On the other hand, biologically synthesized materials often have properties that surpass the properties of the analogous products made
by the synthetic route [32]. Unlike the traditional chemical synthetic process,
biomineralization happens under mild conditions with the help of macromolecules
such as proteins [33]. Thus, biominerals are usually composites in nature due to the
presence of organic molecules; however, these materials are often not only as hard as
the pure mineral but are also tougher [32].
Different organisms are known to be involved in mineral formation. In higher
organisms, biomineralization involves production of cystolith inclusions in leaves
and strong body parts like bones, teeth, and shells. Currently, there are over
60 different mineral groups that are formed by organisms [34, 35] and deposited
in their body for various biological functions. Algal and diatoms silicates, invertebrate carbonates, and vertebrate calcium phosphates and carbonates can be mentioned as examples. As in the case of higher organisms, lower group of organisms,
especially prokaryotes such as bacteria, are highly potent agents of biomineralization. These organisms form an enormous variety of minerals such as carbonates,
298
G. Mamo and B. Mattiasson