free Mn (Mn
2+ ) and the other that acts only on Mn
2+ bound to Mn(IV) oxide and
derive energy from the reaction. At the same time, Arcuri and Ehrlich (1980)
proposed that cytochromes were involved in Mn
2+ oxidation by Oceanospirillum
BIII 45. They could observe that addition of periplasmic/intracellular fraction
to membrane fraction was essential for Mn oxidation. Yet in another study on the
removal efficiency of Mn
2+ from seawater by marine sediments and clay minerals
with the same organism, Ehrlich (1982) observed that ferric chloride pretreatment
of clays is essential when intact cells are used and not when cell-free extracts are
used. He remarked that ferric chloride pretreatment was necessary for activating the
sediment for bacterial oxidation of sorbed Mn
2+ .
Another interesting observation on Mn
2+ oxidation by bacterial isolates from
hydrothermal area (Ehrlich 1983) showed that Mn
2+ oxidation could occur through
an inducible enzyme system and an initial fixation of Mn(II) to Mn(IV) oxide was
not essential for oxidation to proceed. Our earlier observation on the bacteriology of
Fe–Mn nodules from the Indian Ocean region showed that psychrotrophic heterotrophic bacteria were capable of mobilizing and immobilizing Mn. The maximum
percentage of Mn oxidizers (32.2%) was restricted to nodule surface and possessed
various hydrolytic enzymes (Chandramohan et al. 1987). Later on, Ehrlich and
Salerno (1990) demonstrated the coupling of ATP synthesis with that of Mn
2+
oxidation by a marine bacterial strain SSW22. They proposed chemiosmosis
(diffusion of ions across a selectively permeable membrane) as the probable
mechanism for energy coupling by intact cells, membrane vesicles, or cell extracts.
In a different study, Rosson and Nealson (1982) observed that live/killed mature
spores of Bacillus Strain SG-1 could oxidize Mn
2+ once bound but not when free in
solution. They hypothesized that Mn
2+ may form complex with exosporium or a
spore coat protein. In another observation, Kepkay and Nealson (1982) identified
that spores rather than vegetative cells are responsible for Mn
2+ oxidation by SG-1.
The adherence of bacterial cells to solid surfaces was found to be essential for
proper sporulation and Mn
2+ oxidation. Using radiotracers, Emerson et al. (1982)
explained that Mn
2+ oxidation in Saanich Inlet is bacterially mediated and the
removal of Mn
2+ is very fast and would occur in a matter of few days on solid
surfaces. The study on the role of plasmids in Mn
2+ oxidation (Lidstrom et al. 1983;
Schuett et al. 1986) showed that in marine Pseudomonads, increased levels of both
binding and oxidation of Mn
2+ could occur in the presence of plasmids. Using
radiotracers, Tebo et al. (1984) provided evidence for Mn
2+ oxidation with oxygen
as the terminal electron acceptor in Saanich Inlet and Framvaren Fjord. The Mn
2+
oxidation was found to occur faster under air-saturated condition than under
conditions of oxygen limitation. Interestingly, Rosson et al. (1984) using poisoned
control could differentiate biological from abiotic Mn
2+ oxidation and demonstrated that bacteria could significantly enhance the rate of Mn
2+ removal from
manganese-rich particulate layer in the water column. Further, by in situ experimental evidence on Mn
2+ oxidation in Saanich Inlet, Tebo and Emerson (1985)
showed that the rate of Mn
2+ oxidation was limited by both oxygen and the
concentration of microbial binding sites in the environment. In a study on Mn
2+
removal from porewater, Edenborn et al. (1985) observed that Mn
2+ removal rate is
3 Manganese Oxidation by Bacteria: Biogeochemical Aspects
55
2+ ) and the other that acts only on Mn
2+ bound to Mn(IV) oxide and
derive energy from the reaction. At the same time, Arcuri and Ehrlich (1980)
proposed that cytochromes were involved in Mn
2+ oxidation by Oceanospirillum
BIII 45. They could observe that addition of periplasmic/intracellular fraction
to membrane fraction was essential for Mn oxidation. Yet in another study on the
removal efficiency of Mn
2+ from seawater by marine sediments and clay minerals
with the same organism, Ehrlich (1982) observed that ferric chloride pretreatment
of clays is essential when intact cells are used and not when cell-free extracts are
used. He remarked that ferric chloride pretreatment was necessary for activating the
sediment for bacterial oxidation of sorbed Mn
2+ .
Another interesting observation on Mn
2+ oxidation by bacterial isolates from
hydrothermal area (Ehrlich 1983) showed that Mn
2+ oxidation could occur through
an inducible enzyme system and an initial fixation of Mn(II) to Mn(IV) oxide was
not essential for oxidation to proceed. Our earlier observation on the bacteriology of
Fe–Mn nodules from the Indian Ocean region showed that psychrotrophic heterotrophic bacteria were capable of mobilizing and immobilizing Mn. The maximum
percentage of Mn oxidizers (32.2%) was restricted to nodule surface and possessed
various hydrolytic enzymes (Chandramohan et al. 1987). Later on, Ehrlich and
Salerno (1990) demonstrated the coupling of ATP synthesis with that of Mn
2+
oxidation by a marine bacterial strain SSW22. They proposed chemiosmosis
(diffusion of ions across a selectively permeable membrane) as the probable
mechanism for energy coupling by intact cells, membrane vesicles, or cell extracts.
In a different study, Rosson and Nealson (1982) observed that live/killed mature
spores of Bacillus Strain SG-1 could oxidize Mn
2+ once bound but not when free in
solution. They hypothesized that Mn
2+ may form complex with exosporium or a
spore coat protein. In another observation, Kepkay and Nealson (1982) identified
that spores rather than vegetative cells are responsible for Mn
2+ oxidation by SG-1.
The adherence of bacterial cells to solid surfaces was found to be essential for
proper sporulation and Mn
2+ oxidation. Using radiotracers, Emerson et al. (1982)
explained that Mn
2+ oxidation in Saanich Inlet is bacterially mediated and the
removal of Mn
2+ is very fast and would occur in a matter of few days on solid
surfaces. The study on the role of plasmids in Mn
2+ oxidation (Lidstrom et al. 1983;
Schuett et al. 1986) showed that in marine Pseudomonads, increased levels of both
binding and oxidation of Mn
2+ could occur in the presence of plasmids. Using
radiotracers, Tebo et al. (1984) provided evidence for Mn
2+ oxidation with oxygen
as the terminal electron acceptor in Saanich Inlet and Framvaren Fjord. The Mn
2+
oxidation was found to occur faster under air-saturated condition than under
conditions of oxygen limitation. Interestingly, Rosson et al. (1984) using poisoned
control could differentiate biological from abiotic Mn
2+ oxidation and demonstrated that bacteria could significantly enhance the rate of Mn
2+ removal from
manganese-rich particulate layer in the water column. Further, by in situ experimental evidence on Mn
2+ oxidation in Saanich Inlet, Tebo and Emerson (1985)
showed that the rate of Mn
2+ oxidation was limited by both oxygen and the
concentration of microbial binding sites in the environment. In a study on Mn
2+
removal from porewater, Edenborn et al. (1985) observed that Mn
2+ removal rate is
3 Manganese Oxidation by Bacteria: Biogeochemical Aspects
55