The reduction of Mn oxide is predicted based on standard redox potential of
+1.29 mV (Rusin and Ehrlich 1995) based on the equation
1
2
MnO 2 þ 2H
þ
þ e
À
!
1
2
Mn
2þ
þ H 2 O
In environment where Mn and iron oxides coexist such as in ferromanganese
nodules, bacteria preferentially attack manganese oxides. The possible explanation
suggested for the preference of Mn over Fe by bacteria was the lower midpoint
potential for the Fe(III)/Fe(II) couple relative to the Mn(IV)/Mn(II) couple (Ehrlich
1987). However, the exact reason is yet to be determined.
3.4 Effect of Salinity on Manganese Oxidation
The solubility of Mn is more in freshwater compared to salt water. However, the
oxidation rate of Mn
2+ decreased sixfold in creek water of an English estuary when
the salinity of water increased from 1 to 5 (Vojak et al. 1985). Likewise, Spratt et al.
(1994b) also demonstrated a fourfold decrease in the rates of manganese oxide
production in high marsh sediments than in creek bank sediments. In another study,
Spratt et al. (1994a) showed decrease in rate of Mn oxidation in high marsh
sediments experimentally exposed to hypersaline (102) conditions. They demonstrated that Mn oxidation in creek bank sediments exhibit much higher rates of
oxidation than high marsh sites (2.31 Æ 0.28 and 0.45 Æ 0.14 nmol mg dwt
À1 h
À1 ).
In mangrove swamp estuary, highest rates of microbial Mn oxide production was
encountered in sediments with salinities between 0 and 8 (50–119 pmol mg
dwt
À1 h
À1 , respectively) compared with sediments from the mouth of the estuary
with salinities of 24 and 34 (3–16 pmol mg dwt
À1 h
À1 , respectively). Nevertheless,
the overall rates of microbial Mn oxide production in salt-marsh sediments were
much higher than in mangrove sediments.
3.5 Toxicity of Manganese in the Presence of Other Metals
In an undisturbed marine environment, metal ions are more likely to occur in
combinations than in single (Yang and Ehrlich 1976). The microbial response to
individual metals may differ from the response to stress from multiple metals. When
interactions of one metal have a protective effect on the toxicity of other metal, the
resulting effect is referred as antagonistic and the reverse effect where toxicity of one
metal is enhanced in the presence of the other metal is synergistic. Third, interactions
where the final toxicity is simply a sum of the individual toxicities of the metal ions is
called additive (Babich and Stotzky 1983). The effect of Mn, Ni, Cu, and Co in
combinations of 10 mg mL
À1 in seawater enriched with 1% glucose and 0.05%
3 Manganese Oxidation by Bacteria: Biogeochemical Aspects
53
+1.29 mV (Rusin and Ehrlich 1995) based on the equation
1
2
MnO 2 þ 2H
þ
þ e
À
!
1
2
Mn
2þ
þ H 2 O
In environment where Mn and iron oxides coexist such as in ferromanganese
nodules, bacteria preferentially attack manganese oxides. The possible explanation
suggested for the preference of Mn over Fe by bacteria was the lower midpoint
potential for the Fe(III)/Fe(II) couple relative to the Mn(IV)/Mn(II) couple (Ehrlich
1987). However, the exact reason is yet to be determined.
3.4 Effect of Salinity on Manganese Oxidation
The solubility of Mn is more in freshwater compared to salt water. However, the
oxidation rate of Mn
2+ decreased sixfold in creek water of an English estuary when
the salinity of water increased from 1 to 5 (Vojak et al. 1985). Likewise, Spratt et al.
(1994b) also demonstrated a fourfold decrease in the rates of manganese oxide
production in high marsh sediments than in creek bank sediments. In another study,
Spratt et al. (1994a) showed decrease in rate of Mn oxidation in high marsh
sediments experimentally exposed to hypersaline (102) conditions. They demonstrated that Mn oxidation in creek bank sediments exhibit much higher rates of
oxidation than high marsh sites (2.31 Æ 0.28 and 0.45 Æ 0.14 nmol mg dwt
À1 h
À1 ).
In mangrove swamp estuary, highest rates of microbial Mn oxide production was
encountered in sediments with salinities between 0 and 8 (50–119 pmol mg
dwt
À1 h
À1 , respectively) compared with sediments from the mouth of the estuary
with salinities of 24 and 34 (3–16 pmol mg dwt
À1 h
À1 , respectively). Nevertheless,
the overall rates of microbial Mn oxide production in salt-marsh sediments were
much higher than in mangrove sediments.
3.5 Toxicity of Manganese in the Presence of Other Metals
In an undisturbed marine environment, metal ions are more likely to occur in
combinations than in single (Yang and Ehrlich 1976). The microbial response to
individual metals may differ from the response to stress from multiple metals. When
interactions of one metal have a protective effect on the toxicity of other metal, the
resulting effect is referred as antagonistic and the reverse effect where toxicity of one
metal is enhanced in the presence of the other metal is synergistic. Third, interactions
where the final toxicity is simply a sum of the individual toxicities of the metal ions is
called additive (Babich and Stotzky 1983). The effect of Mn, Ni, Cu, and Co in
combinations of 10 mg mL
À1 in seawater enriched with 1% glucose and 0.05%
3 Manganese Oxidation by Bacteria: Biogeochemical Aspects
53