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for bacterially mediated/induced mineralization.
This review will attempt to show that, with the
exception of bacterially controlled mineralization
by magnetobacteria (Bazylinsky & Moskowitz
1997), the mechanisms which control bacterial
biomineralization are not mineral- or bacterium-
specific, but rather appear to be universal: they
seem to depend on the environment in which
bacteria dwell and not on any specific type of
bacteria. It is believed that this can be evidenced
by evaluating how Myxococcus activity induces
mineral precipitation.
controversy on the origins of natural dolomite (the
so-called 'dolomite problem'). The suggestion that
carbonates in Martian meteorite ALH84001 could
be bacterial in origin (McKay et al. 1996) has
prompted much debate. These Martian carbonate
microfossils were assumed to be precipitated by
dwarf bacteria, the so-called 'nanobacteria' (Folk
1993), the existence of which has been strongly
disputed (e.g. Kirkland et al. 1999; Southan &
Donald 1999). For instance, Aloisi et al. (2006)
have shown that such calcified 'nanobacteria' are
in fact nanoglobules originated from bacterial cell
surface that act as calcium carbonate nucleation
sites once released into the culture medium. In
general,
Types of minerals produced by bacterially
induced or mediated processes
recognition
of
microbial
carbonates
in
nature is controversial (Riding 2000).
Iron oxides and hydroxides have been observed
to precipitate within, on and outside microbial cells
(Konhauser 1998). Magnetite (Fe
3
O
4
) appeared to
form the striking precipitates lined in magneto-
somes of magnetotactic bacteria (Bazylinski &
Moskowitz 1997). Komeili et al. (2004) have shown
that a magnetosome-associated protein, MamA, is
required for the formation of functional magneto-
somes and the growth of magnetite in magnetotactic
bacteria. These works proved the intimate relation-
ship between cell biology and bacterially contro-
lled mineralization. Iron oxyhydroxides such as
ferrihydrite (Fe
2
O
3
.
0.5H
2
O) precipitate on bacterial
cells (Casanova et al. 1999; Banfield et al. 2000).
Chan et al. (2004) reported bacterial precipitation
of akaganeite (FeOOH) pseudo-single crystals
with unusual 1000:1 aspect ratios. They concluded
that the bacterial cells extruded the polysaccharide
strands to localize FeOOH precipitation in proxi-
mity to the cell membrane. Such work has opened
new ways for engineering novel materials. Ferris
et al. (1988) concluded that iron binding to and silica
precipitation on bacterial cells was an important
contributing factor to the fossilization of microbes.
It should be indicated that the Fe(II) - Fe(III) redox
cycle represents a major energy flux at the Earth
surface (Lower et al. 2001). Schewanella is known
to be an active element in this cycle by contributing
to Fe reduction and the precipitation of iron oxides
(Lower et al. 2001). Bacterial mineralization of
other metal oxides such as Mn, has also been
reported (Fortin et al. 1998; Northup & Lavoie
2001). For instance, several studies have proposed
microbial participation in the formation of cave
manganese deposits that include pyrolusite (MnO
2
),
romanechite (Ba
0.7
Mn
4.8
Si
0.1
O
10
.
1.2H
2
O), todoro-
kite (Na
0.2
Ca
0.05
K
0.02
Mn
4
4
Mn
3
2
O
12
.
3H
2
O), and bir-
messite (Na
0.3
Ca
0.1
K
0.1
Mn
4þ
Mn
3þ
O
4
.
1.5H
2
O) (see
review by Northup & Lavoie 2001).
Bacterially induced or mediated precipitation
of iron and manganese oxides is commonly asso-
ciated with Siderocapsa, Gallionella, Leptothrix,
Several pioneering works on the role of bacteria in
mineral precipitation were published during the
19th century (see Ehrlich 2002 and references
therein). However, it was not until the early 20th
century that the study of bacterial mineralization
gained momentum. Drew (1914) demonstrated
that bacteria isolated from natural marine waters
were able to precipitate calcium carbonate. This
type of research prompted the systematic study of
possible associations between bacteria and mineral
precipitation. Since then, it has been shown that
different kinds of bacteria produce mineral precipi-
tates in both laboratory and natural environments
(Banfield
&
Nealson
1997;
McIntosh
&
Groat
1997; Ehrlich 2002).
A substantial amount of research has focused
on the precipitation of carbonate minerals (Boquet
et al. 1973; Buczynski & Chafetz 1991; Knorre &
Krumbein 2000; Rodriguez-Navarro et al. 2003;
Ben Chekroun et al. 2004). Bacterial precipitation
of calcium carbonate polymorphs (calcite, aragonite
and vaterite) (Ben Chekroun et al. 2004; Rodriguez-
Navarro et al. 2007) has become an attractive
research topic because it has important implications
in past and present formation of carbonate rocks and
sediments (Krumbein 1979; Buczynski & Chafetz
1991; Braissant et al. 2003; Dupraz & Visscher
2005). Besides its geological significance, bacterial
carbonate precipitation in terrestrial environments
appears to be crucial for atmospheric CO
2
budgeting
(Braissant et al. 2002). While early work (until the
1980s) examined the ability of bacteria to precipi-
tate calcium carbonates in marine environments,
precipitation of carbonates in other environments
such as lakes, travertines, caves, soils and monu-
ments, has become the subject of much research in
recent decades (Boquet et al. 1973; Chafetz &
Folk 1984; Folk 1993; Urzi et al. 1999; Blyth &
Frisia 2008). The study of dolomite [CaMg(CO
3
)
2
]
precipitation in the presence of bacteria (Vasconce-
los et al. 1995) is helping to solve the long standing
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