phenol, propanol, propionate, pyruvate, toluene, valerate
(Lovley 2006). Some examples (Lovley 1991):
benzoate
À
þ 30 Fe III
ð Þ þ 19 H 2 O
! 7 HCO 3
À
þ 30 Fe II
ð Þ þ 36 H
þ
toluene þ 36 Fe III
ð Þ þ 21 H 2 O
! 7 HCO 3
À
þ 36 Fe II
ð Þ þ 43 H
þ
phenol þ 28 Fe III
ð Þ þ 17 H 2 O
! 6 HCO 3
À
þ 28 Fe II
ð Þ þ 34 H
þ
p‐cresol þ 34 Fe III
ð Þ þ 20 H 2 O
! 7 HCO 3
À
þ 34 Fe II
ð Þ þ 41 H
þ
Metabolism of sugars has also been demonstrated. It
produces enough energy to allow growth; oxidation may be
total (Ku ¨sel et al. 1999) or incomplete (Coates et al. 1998):
C 6 H 12 O 6 þ 2 H 2 O þ 8 Fe III
ð Þ
! 2 CH 3 COOH þ 2 CO 2 þ 8 Fe II
ð Þ þ 8 H
þ
C 6 H 12 O 6 þ 24 Fe III
ð Þ þ 24 OH
À
! 6 CO 2 þ 24 Fe II
ð Þ þ 18 H 2 O
The metabolic capacities of microbial iron-reducers have
many environmental applications. The Geobacteraceae can
play an important role in the rehabilitation of deep anoxic
environments contaminated with aromatic hydrocarbons
(benzene, toluene, ethylbenzene, o-xylene, p-cresol, phenol). Their action in the cleanup of groundwaters or
sediments contaminated by hydrocarbons was observed
and provides opportunities for the development of remediation techniques against contaminated sites (Jahn et al. 2005)
(cf. Sect. 16.8.3).
14.5.3 The Cycle of Manganese
14.5.3.1 Manganese in the Environment
The abundance of manganese in the earth’s crust was
estimated to be 0.1 %. Manganese can exist in different
oxidation states ranging from 0 to +VII (permanganate). In
the nature, only the states +II, +III, and +IV are commonly
found. The oxidation state of manganese is influenced by
chemical and physical characteristics of their environment.
In reduced sediments and at low pH, the form Mn(II), equivalent to the soluble manganese ion Mn
2+ , is the most abundant. The appearance of the insoluble (in water) oxidized
form, Mn(IV) that corresponds to the manganese dioxide
(MnO 2 ), is favored at high pH and in oxidized environments.
However, even if environmental conditions favor changes in
the oxidation state, these chemical conversions are slow. The
oxidation and reduction of manganese in many biotopes are
mainly related to bacterial metabolism.
In some marine and freshwater habitats, precipitation of
manganese forms the so-called polymetallic nodules which
also contain other elements. Chemical analysis of these
nodules shows that they mainly consist of manganese
(20–30 %) and iron (6–15 %). Other metallic elements
such as nickel (1.34 %), copper (1.25 %), cobalt (0.25 %),
titanium (0.60 %), and aluminum (2.90 %) are also present
in these nodules. They also contain sodium, magnesium,
silica, oxygen, and hydrogen. The problem of the genesis
of these nodules is far from being resolved. Four origins are
possible:
1. “Hydrogenated”, slow precipitation of metallic elements
from seawater which leads to concretions with equivalent
concentrations of Fe and Mn and relatively high Ni, Cu,
and Co contents;
2. “Hydrothermal”, giving concretions which are generally
rich in iron and poor in Mn, Ni, Cu, and Co;
3. “Diagenetic,” known from the remobilization of manganese in the sediments and its precipitation at the watersediment interface, giving nodules which are rich in Mn
and poor in Fe, Ni, Cu, and Co;
4. “Halmyrolitic,” where the source of metallic compounds
is the attack of basaltic debris by seawater
These theories, termed “mineral theories,” contrast with
the so-called “biologic theories” (Graham and Cooper 1959)
where detritus from organisms are responsible for the
enrichments in Cu and Ni.
14.5.3.2 Biological Functions
Manganese is an essential trace element in several biological
systems. It is essential in the diet of micro-organisms, plants,
and animals. It is necessary in the oxygenic photosynthesis
where it is involved in the functioning of photosystem II. It is
also a cofactor of various enzymes such as pyruvate kinase
which is involved in glycolysis. For some bacteria, the Mn
(II) can be used as an energy source and the forms Mn(III)
and Mn(IV) as terminal electron acceptors. The importance
of microorganisms that are capable to oxidize and reduce
the manganese is demonstrated by their ubiquity in terrestrial, freshwater, and marine environments. After oxygen,
manganese oxides are among the most effective oxidizing
agents encountered in the environment.
14.5.3.3 Oxidation by Microorganisms
In the nature, Mn oxidation takes place in two ways: either
by spontaneous reaction which is enhanced in alkaline
conditions or by enzymatic reactions (Fig. 14.48). The
608
J.-C. Bertrand et al.
(Lovley 2006). Some examples (Lovley 1991):
benzoate
À
þ 30 Fe III
ð Þ þ 19 H 2 O
! 7 HCO 3
À
þ 30 Fe II
ð Þ þ 36 H
þ
toluene þ 36 Fe III
ð Þ þ 21 H 2 O
! 7 HCO 3
À
þ 36 Fe II
ð Þ þ 43 H
þ
phenol þ 28 Fe III
ð Þ þ 17 H 2 O
! 6 HCO 3
À
þ 28 Fe II
ð Þ þ 34 H
þ
p‐cresol þ 34 Fe III
ð Þ þ 20 H 2 O
! 7 HCO 3
À
þ 34 Fe II
ð Þ þ 41 H
þ
Metabolism of sugars has also been demonstrated. It
produces enough energy to allow growth; oxidation may be
total (Ku ¨sel et al. 1999) or incomplete (Coates et al. 1998):
C 6 H 12 O 6 þ 2 H 2 O þ 8 Fe III
ð Þ
! 2 CH 3 COOH þ 2 CO 2 þ 8 Fe II
ð Þ þ 8 H
þ
C 6 H 12 O 6 þ 24 Fe III
ð Þ þ 24 OH
À
! 6 CO 2 þ 24 Fe II
ð Þ þ 18 H 2 O
The metabolic capacities of microbial iron-reducers have
many environmental applications. The Geobacteraceae can
play an important role in the rehabilitation of deep anoxic
environments contaminated with aromatic hydrocarbons
(benzene, toluene, ethylbenzene, o-xylene, p-cresol, phenol). Their action in the cleanup of groundwaters or
sediments contaminated by hydrocarbons was observed
and provides opportunities for the development of remediation techniques against contaminated sites (Jahn et al. 2005)
(cf. Sect. 16.8.3).
14.5.3 The Cycle of Manganese
14.5.3.1 Manganese in the Environment
The abundance of manganese in the earth’s crust was
estimated to be 0.1 %. Manganese can exist in different
oxidation states ranging from 0 to +VII (permanganate). In
the nature, only the states +II, +III, and +IV are commonly
found. The oxidation state of manganese is influenced by
chemical and physical characteristics of their environment.
In reduced sediments and at low pH, the form Mn(II), equivalent to the soluble manganese ion Mn
2+ , is the most abundant. The appearance of the insoluble (in water) oxidized
form, Mn(IV) that corresponds to the manganese dioxide
(MnO 2 ), is favored at high pH and in oxidized environments.
However, even if environmental conditions favor changes in
the oxidation state, these chemical conversions are slow. The
oxidation and reduction of manganese in many biotopes are
mainly related to bacterial metabolism.
In some marine and freshwater habitats, precipitation of
manganese forms the so-called polymetallic nodules which
also contain other elements. Chemical analysis of these
nodules shows that they mainly consist of manganese
(20–30 %) and iron (6–15 %). Other metallic elements
such as nickel (1.34 %), copper (1.25 %), cobalt (0.25 %),
titanium (0.60 %), and aluminum (2.90 %) are also present
in these nodules. They also contain sodium, magnesium,
silica, oxygen, and hydrogen. The problem of the genesis
of these nodules is far from being resolved. Four origins are
possible:
1. “Hydrogenated”, slow precipitation of metallic elements
from seawater which leads to concretions with equivalent
concentrations of Fe and Mn and relatively high Ni, Cu,
and Co contents;
2. “Hydrothermal”, giving concretions which are generally
rich in iron and poor in Mn, Ni, Cu, and Co;
3. “Diagenetic,” known from the remobilization of manganese in the sediments and its precipitation at the watersediment interface, giving nodules which are rich in Mn
and poor in Fe, Ni, Cu, and Co;
4. “Halmyrolitic,” where the source of metallic compounds
is the attack of basaltic debris by seawater
These theories, termed “mineral theories,” contrast with
the so-called “biologic theories” (Graham and Cooper 1959)
where detritus from organisms are responsible for the
enrichments in Cu and Ni.
14.5.3.2 Biological Functions
Manganese is an essential trace element in several biological
systems. It is essential in the diet of micro-organisms, plants,
and animals. It is necessary in the oxygenic photosynthesis
where it is involved in the functioning of photosystem II. It is
also a cofactor of various enzymes such as pyruvate kinase
which is involved in glycolysis. For some bacteria, the Mn
(II) can be used as an energy source and the forms Mn(III)
and Mn(IV) as terminal electron acceptors. The importance
of microorganisms that are capable to oxidize and reduce
the manganese is demonstrated by their ubiquity in terrestrial, freshwater, and marine environments. After oxygen,
manganese oxides are among the most effective oxidizing
agents encountered in the environment.
14.5.3.3 Oxidation by Microorganisms
In the nature, Mn oxidation takes place in two ways: either
by spontaneous reaction which is enhanced in alkaline
conditions or by enzymatic reactions (Fig. 14.48). The
608
J.-C. Bertrand et al.