C. acetobutylicum, an increase in NADH accumulation was expected. Experimental
data showed cytoplasmic levels of NADH 37 times higher in the mutant than in the
wild-type strain (Marvasi et al. 2010). Cytosolic accumulation of NADH could
explain proton extrusion excess. If this deregulated proton extrusion might interfere
with the active coupled Ca
2+ /2H
+ transport through membrane involved in
the precipitation model proposed by Hammes and Verstraete (2002; Fig. 5.3), it
remains at the moment only a hypothesis.
5.3.2.2 Evolution and Meaning of CC Mineralization By Organisms
Since the early Precambrian, microbes have had an impact on the evolution of
the Earth’s surface, including the uppermost lithosphere and hydrosphere, as well
as of the atmosphere (Ehrlich 1998). During the Precambrian, the calcium cycle
(with both deposition and dissolution phenomena) was sustained by the prokaryotes,
and played a key part in the emergence of the biosphere (Zavarzin 2002). The
participation of bacteria in the geochemical calcium cycle is the most important
factor maintaining neutral conditions on Earth. This cycle has profound influence on
the fate of inorganic carbon, and, thereby, on the removal of CO 2 from the primitive
atmosphere. Deposition of CaCO 3 minerals is one of the main processes of the
biogeochemical calcium cycle. Most calcium deposits were formed in the Precambrian, when the prokaryotic biosphere predominated, as proved by the extensive
development of stromatolite deposits. After that, calcium recycling based on biogenic deposition by skeletal organisms became the main process (Zavarzin 2002).
The ability of CC mineralization, as well as other biomineralization processes
evolved then with prokaryotes (Ben Omar et al. 1997), even if apparently without a
specific aim or function (Zavarzin 2002). The necessity to immobilize calcium
outside the cell to avoid intracellular [Ca
2+ ] rising to dangerous levels might have
enabled bacteria to produce CaCO 3 , as discussed above. Similarly to what might
have occurred to Prokaryotes, calcium biomineralization could have occurred as
an accident also to eukaryotes, which might have made a virtue of necessity.
According to Brennan et al. (2004), marine shells would be a form of solid waste
produced by marine organisms due to a geologic process which filled oceans with
calcium. One of the most dramatic and confounding events in evolutionary and
geologic history (an unresolved issue in Earth’s history) was the sudden onset of
biomineralization in the Early Cambrian during the “Cambrian explosion”, i.e., the
sudden onset of hard structures of insoluble calcium minerals built by organisms by
biologically controlled calcification (see Sect. 5.2.1). Brennan et al. (2004)
analyzed major ion composition of primary fluid inclusions (evaporated seawater)
in Terminal Proterozoic (ca. 544 Ma) and Early Cambrian (ca. 515 Ma) marine
halites and found that the major ion composition of seawater changed between
544 Ma and 515 Ma, highlighted by a large increase (threefold higher) in [Ca
2+ ].
The timing of this shift in seawater chemistry broadly coincides with the “Cambrian
explosion”, a brief drop in marine 87Sr/86Sr values, and an increase in tectonic
activity, suggesting a link between the advent of biocalcification, hydrothermal
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B. Perito and G. Mastromei
data showed cytoplasmic levels of NADH 37 times higher in the mutant than in the
wild-type strain (Marvasi et al. 2010). Cytosolic accumulation of NADH could
explain proton extrusion excess. If this deregulated proton extrusion might interfere
with the active coupled Ca
2+ /2H
+ transport through membrane involved in
the precipitation model proposed by Hammes and Verstraete (2002; Fig. 5.3), it
remains at the moment only a hypothesis.
5.3.2.2 Evolution and Meaning of CC Mineralization By Organisms
Since the early Precambrian, microbes have had an impact on the evolution of
the Earth’s surface, including the uppermost lithosphere and hydrosphere, as well
as of the atmosphere (Ehrlich 1998). During the Precambrian, the calcium cycle
(with both deposition and dissolution phenomena) was sustained by the prokaryotes,
and played a key part in the emergence of the biosphere (Zavarzin 2002). The
participation of bacteria in the geochemical calcium cycle is the most important
factor maintaining neutral conditions on Earth. This cycle has profound influence on
the fate of inorganic carbon, and, thereby, on the removal of CO 2 from the primitive
atmosphere. Deposition of CaCO 3 minerals is one of the main processes of the
biogeochemical calcium cycle. Most calcium deposits were formed in the Precambrian, when the prokaryotic biosphere predominated, as proved by the extensive
development of stromatolite deposits. After that, calcium recycling based on biogenic deposition by skeletal organisms became the main process (Zavarzin 2002).
The ability of CC mineralization, as well as other biomineralization processes
evolved then with prokaryotes (Ben Omar et al. 1997), even if apparently without a
specific aim or function (Zavarzin 2002). The necessity to immobilize calcium
outside the cell to avoid intracellular [Ca
2+ ] rising to dangerous levels might have
enabled bacteria to produce CaCO 3 , as discussed above. Similarly to what might
have occurred to Prokaryotes, calcium biomineralization could have occurred as
an accident also to eukaryotes, which might have made a virtue of necessity.
According to Brennan et al. (2004), marine shells would be a form of solid waste
produced by marine organisms due to a geologic process which filled oceans with
calcium. One of the most dramatic and confounding events in evolutionary and
geologic history (an unresolved issue in Earth’s history) was the sudden onset of
biomineralization in the Early Cambrian during the “Cambrian explosion”, i.e., the
sudden onset of hard structures of insoluble calcium minerals built by organisms by
biologically controlled calcification (see Sect. 5.2.1). Brennan et al. (2004)
analyzed major ion composition of primary fluid inclusions (evaporated seawater)
in Terminal Proterozoic (ca. 544 Ma) and Early Cambrian (ca. 515 Ma) marine
halites and found that the major ion composition of seawater changed between
544 Ma and 515 Ma, highlighted by a large increase (threefold higher) in [Ca
2+ ].
The timing of this shift in seawater chemistry broadly coincides with the “Cambrian
explosion”, a brief drop in marine 87Sr/86Sr values, and an increase in tectonic
activity, suggesting a link between the advent of biocalcification, hydrothermal
132
B. Perito and G. Mastromei