Our observation on microbially mediated Mn
2+ oxidation in bacterial isolates
belonging to Halomonas sp from Carlsberg Ridge (Fernandes et al. 2005) showed
that Mn is precipitated extracellularly. Same isolates when grown in the presence of
Ni and Co in the absence of Mn
2+ showed the ability to accumulate these metals
both intra- and extracellularly (Sujith et al. 2010; Antony et al. 2010). Further, study
from the mangrove sediments Krishnan et al. (2007) offered experimental evidence
to demonstrate that both autochthonous autotrophs and heterotrophs work in tandem in reducing Mn
2+ and other related metal ions in sediments. These processes
may indirectly promote more metal oxidation by removing end product inhibition.
3.7 Manganese Oxidation by Freshwater Bacteria
The Mn and Fe oxidizing/depositing bacteria in freshwater habitats belong to
Sphaerotilus, Gallionella, Leptothrix, Pedomicrobium, Metallogenium, Hyphomicrobium, Crenothrix, Clonothrix, and Cladothrix groups (Gregory and Staley
1982; Ghiorse 1984). Based on their abundance, Pringsheim (1949) stated that
their significance in biochemical processes in rivers must be great but require
further investigations to know about their nutritional needs, metabolism, and
enzymatic systems. Knowing the importance of Mn
2+ oxidation by bacteria, Johnson and Stokes (1966) readily stated with experimental evidence that Sphaerotilus
discophorus belonging to b 1 subdivision of proteobacteria could oxidize Mn
2+ to
dark-brown manganic oxide. They pointed out that cells can lose the Mn
2+ -
oxidizing activity on heating and not poisoned by treatment with HgCl 2 suggestive
of endogenous Mn
2+ oxidation catalyzed by an inducible enzyme(s). In continuation of the earlier study with Sphaerotilus discophorus, Stokes and Powers (1967)
ruled out that endogenous oxidation of Mn
2+ could be stimulated by the oxidation
of poly-b-hydroxybutyrate, a storage product within the cell. Further study by Ali
and Stokes (1971) could observe autotrophic growth promotion in Sphaerotilus
discophorus with Mn
2+ as the sole source of energy. The results were later on
evaluated with evidence that in the late phase of growth, S. discophorus do oxidize
and accumulate MnO 2 but do not serve as energy source in this organism (Hajj and
Makemson 1976). Conversely, Mills and Randles (1979) using electron transport
chain inhibitors in their study suggested that Mn
2+ oxidation in Sphaerotilus
discophorus could be cytochrome mediated.
In an another study with different Mn-oxidizing filamentous budding bacteria
Pedomicrobium belonging to a-proteobacteria, Ghiorse and Hirsch (1978) noted
that very active Mn-depositing bacterial strains are also very active iron depositors.
The presence of budding bacteria in freshwater distribution systems leads to the
formation of biofilms heavily encrusted with Mn oxides (Tyler and Marshall 1967;
Sly et al. 1988). The depositions of Mn oxides occur in close association with an
extracellular matrix of acidic polysaccharides or polymer in these bacterial strains
3 Manganese Oxidation by Bacteria: Biogeochemical Aspects
57
2+ oxidation in bacterial isolates
belonging to Halomonas sp from Carlsberg Ridge (Fernandes et al. 2005) showed
that Mn is precipitated extracellularly. Same isolates when grown in the presence of
Ni and Co in the absence of Mn
2+ showed the ability to accumulate these metals
both intra- and extracellularly (Sujith et al. 2010; Antony et al. 2010). Further, study
from the mangrove sediments Krishnan et al. (2007) offered experimental evidence
to demonstrate that both autochthonous autotrophs and heterotrophs work in tandem in reducing Mn
2+ and other related metal ions in sediments. These processes
may indirectly promote more metal oxidation by removing end product inhibition.
3.7 Manganese Oxidation by Freshwater Bacteria
The Mn and Fe oxidizing/depositing bacteria in freshwater habitats belong to
Sphaerotilus, Gallionella, Leptothrix, Pedomicrobium, Metallogenium, Hyphomicrobium, Crenothrix, Clonothrix, and Cladothrix groups (Gregory and Staley
1982; Ghiorse 1984). Based on their abundance, Pringsheim (1949) stated that
their significance in biochemical processes in rivers must be great but require
further investigations to know about their nutritional needs, metabolism, and
enzymatic systems. Knowing the importance of Mn
2+ oxidation by bacteria, Johnson and Stokes (1966) readily stated with experimental evidence that Sphaerotilus
discophorus belonging to b 1 subdivision of proteobacteria could oxidize Mn
2+ to
dark-brown manganic oxide. They pointed out that cells can lose the Mn
2+ -
oxidizing activity on heating and not poisoned by treatment with HgCl 2 suggestive
of endogenous Mn
2+ oxidation catalyzed by an inducible enzyme(s). In continuation of the earlier study with Sphaerotilus discophorus, Stokes and Powers (1967)
ruled out that endogenous oxidation of Mn
2+ could be stimulated by the oxidation
of poly-b-hydroxybutyrate, a storage product within the cell. Further study by Ali
and Stokes (1971) could observe autotrophic growth promotion in Sphaerotilus
discophorus with Mn
2+ as the sole source of energy. The results were later on
evaluated with evidence that in the late phase of growth, S. discophorus do oxidize
and accumulate MnO 2 but do not serve as energy source in this organism (Hajj and
Makemson 1976). Conversely, Mills and Randles (1979) using electron transport
chain inhibitors in their study suggested that Mn
2+ oxidation in Sphaerotilus
discophorus could be cytochrome mediated.
In an another study with different Mn-oxidizing filamentous budding bacteria
Pedomicrobium belonging to a-proteobacteria, Ghiorse and Hirsch (1978) noted
that very active Mn-depositing bacterial strains are also very active iron depositors.
The presence of budding bacteria in freshwater distribution systems leads to the
formation of biofilms heavily encrusted with Mn oxides (Tyler and Marshall 1967;
Sly et al. 1988). The depositions of Mn oxides occur in close association with an
extracellular matrix of acidic polysaccharides or polymer in these bacterial strains
3 Manganese Oxidation by Bacteria: Biogeochemical Aspects
57