key factors in BCCP (Beveridge 1989; Fortin et al. 1997; Douglas and Beveridge
1998).
Carbonate precipitation is essentially a function of carbonate alkalinity and the
availability of free calcium ions (Dupraz et al. 2009; Decho 2010), the two are
combined as a saturation index (SI). Concentrations of both free carbonate CO 3
2À
and Ca
2+ ions must exceed saturation for precipitation to occur.
According to Hammes and Verstraete (2002), CCP is a rather straightforward
chemical process governed by four key factors: (1) the calcium (Ca
2+ ) concentration, (2) the concentration of dissolved inorganic carbon (DIC), (3) the pH, and (4)
the availability of nucleation sites. The primary role of bacteria in the precipitation
process has been ascribed to their ability to create an alkaline environment by an
increase in pH to 8.0 and higher and a DIC increase through various physiological
activities (Castanier et al. 1999; Douglas and Beveridge 1998). Bacterial cells are
able to induce pH variations in the medium as a consequence of both metabolic
processes and ion input, which affect the pH in the surrounding microenvironment
(Fortin et al. 1997). Influence of bacterial metabolism on CCP is discussed in
Sect. 5.3.1.
Bacterial surfaces also play an important role in calcium precipitation (Fortin
et al. 1997). Surface bacterial (macro)molecules can induce CCP, providing a
template for carbonate nucleation, both as part of bacterial cell and as cell-free,
when released in the environment; in the latter case, primarily as esopolymeric
substances. Influence of bacterial surfaces on CCP is discussed in Sect. 5.4.
5.2.3 Bacterial CC Minerals
With the singular exception of Achromatium oxaliferum, which precipitates intracellular calcium carbonate crystals (Head et al. 1996), bacteria act upon calcium
compounds in the extracellular space and form CC minerals outside their cell. With
the exception of several cyanobacteria (Zavarzin 2002), prokaryotes do not build
particular inorganic structures of CC, but simple crystals.
Calcite, aragonite, and vaterite are the major crystalline structural polymorphs of
CaCO 3 in bacterial systems, as well as in all biogenic systems (Ben Omar et al.
1997), with the first two as the most represented isoforms and vaterite as the less
stable one. Mineral crystals often contain “substituent elements”, i.e., Mg
2+ ion
often substituted for Ca
2+ in CC precipitates under marine conditions (Decho 2010).
Calcium–magnesium carbonates are frequently produced by bacteria, i.e., dolomite
(Vasconcelos et al. 1995) or magnesium calcite and high-magnesium calcite
(Rivadeneyra et al. 1998; Decho 2010). The isoform produced (vaterite, aragonite,
or calcite) depends both on its growing features and the bacterial strain; different
bacteria precipitate different types of calcium carbonate, and the most common
crystalline forms are either spherical or polyhedral.
The same organism or species can form different kind of minerals in different
environmental conditions (Ben Omar et al. 1997; Brennan et al. 2004; Rivadeneyra
5 Molecular Basis of Bacterial Calcium Carbonate Precipitation
119
1998).
Carbonate precipitation is essentially a function of carbonate alkalinity and the
availability of free calcium ions (Dupraz et al. 2009; Decho 2010), the two are
combined as a saturation index (SI). Concentrations of both free carbonate CO 3
2À
and Ca
2+ ions must exceed saturation for precipitation to occur.
According to Hammes and Verstraete (2002), CCP is a rather straightforward
chemical process governed by four key factors: (1) the calcium (Ca
2+ ) concentration, (2) the concentration of dissolved inorganic carbon (DIC), (3) the pH, and (4)
the availability of nucleation sites. The primary role of bacteria in the precipitation
process has been ascribed to their ability to create an alkaline environment by an
increase in pH to 8.0 and higher and a DIC increase through various physiological
activities (Castanier et al. 1999; Douglas and Beveridge 1998). Bacterial cells are
able to induce pH variations in the medium as a consequence of both metabolic
processes and ion input, which affect the pH in the surrounding microenvironment
(Fortin et al. 1997). Influence of bacterial metabolism on CCP is discussed in
Sect. 5.3.1.
Bacterial surfaces also play an important role in calcium precipitation (Fortin
et al. 1997). Surface bacterial (macro)molecules can induce CCP, providing a
template for carbonate nucleation, both as part of bacterial cell and as cell-free,
when released in the environment; in the latter case, primarily as esopolymeric
substances. Influence of bacterial surfaces on CCP is discussed in Sect. 5.4.
5.2.3 Bacterial CC Minerals
With the singular exception of Achromatium oxaliferum, which precipitates intracellular calcium carbonate crystals (Head et al. 1996), bacteria act upon calcium
compounds in the extracellular space and form CC minerals outside their cell. With
the exception of several cyanobacteria (Zavarzin 2002), prokaryotes do not build
particular inorganic structures of CC, but simple crystals.
Calcite, aragonite, and vaterite are the major crystalline structural polymorphs of
CaCO 3 in bacterial systems, as well as in all biogenic systems (Ben Omar et al.
1997), with the first two as the most represented isoforms and vaterite as the less
stable one. Mineral crystals often contain “substituent elements”, i.e., Mg
2+ ion
often substituted for Ca
2+ in CC precipitates under marine conditions (Decho 2010).
Calcium–magnesium carbonates are frequently produced by bacteria, i.e., dolomite
(Vasconcelos et al. 1995) or magnesium calcite and high-magnesium calcite
(Rivadeneyra et al. 1998; Decho 2010). The isoform produced (vaterite, aragonite,
or calcite) depends both on its growing features and the bacterial strain; different
bacteria precipitate different types of calcium carbonate, and the most common
crystalline forms are either spherical or polyhedral.
The same organism or species can form different kind of minerals in different
environmental conditions (Ben Omar et al. 1997; Brennan et al. 2004; Rivadeneyra
5 Molecular Basis of Bacterial Calcium Carbonate Precipitation
119