oxidation in their study differed with increase in salinity and were depressed in the
presence of inhibitors. Similarly, Johnson and Kipphut (1988) showed by in situ
incubation technique, the rate of Mn
2+ oxidation is largely microbially mediated in
Toolik lake and is regulated by Mn
2+ concentration rather than temperature or
oxygen concentration. With more detailed experiment on mutants that lack the
ability to oxidize Mn
2+ , Caspi et al. (1998) stated that the Mn-oxidizing ability of
Pseudomonas putida MnB1 can be recovered by complementation of the mutation
in a c-type cytochrome biogenesis-defective mutant. In the kinetic studies on Mn
uptake and oxidation by Moy et al. (2003), the uptake of Mn
2+ by Rhizobium sp was
greater than the conversion of Mn
2+ to Mn oxides with significant production of
polysaccharides. They suggested that polysaccharides might be involved in the
uptake of Mn and in minimizing Mn oxide production. The study on redox
transformation of Mn in Antarctic lakes (Krishnan et al. 2009) showed that Co
could have a more profound role in Mn
2+ oxidation and Ni on Mn oxide reduction.
Although several studies report the oxidation of Mn
2+ by bacteria, the identity of
Mn-oxidizing bacteria remained undisclosed. Recently, Falamin and Pinevich
(2006) determined the phylogenetic position and phenotypic properties of Pseudomonas siderocapsa sp.nov. They suggested a mixotrophic mode of nutrition in the
strain and deposition of Mn oxides in their capsules rather than in outer membrane
as observed in other Pseudomonas species.
As an attempt to understand the Mn-oxidizing ability of Leptothrix discophora
SS-1 Adams and Ghiorse (1986) examined the ultrastructure of the strain by
electron microscopy. They could observe extracellular blebs in cells and proposed
it as vehicles for Mn-oxidizing protein. Manganese oxidation by sheathless strain
of Leptothrix discophora SS-1 belonging to b 1 subdivision of proteobacteria
(Boogerd and de Vrind 1987) in buffered medium at pH 7.5 showed the release
of Mn
2+ -oxidizing factors in the spent culture medium and was found associated
with MnO 2 aggregates. Meanwhile, Adams and Ghiorse (1987) isolated the Mn
2+ -
oxidizing protein from Leptothrix discophora SS-1 and characterized the extracellular Mn
2+ -oxidizing activity. The same authors in 1988 identified the oxidation states of Mn in the Mn oxide produced by Leptothrix discophora SS-1. They
could identify that the oxidation state of Mn in fresh samples exist as Mn
3+ and on
aging give rise to a mixture of Mn (III,IV) oxides in older samples. Later, study by
Corstjens et al. (1997) could identify that gene mofA is linked to Mn oxidation. In
addition, Nelson et al. (1999) showed that Mn oxides produced by SS-1 can
adsorb toxic metal lead. Moreover, Brouwers et al. (2000b) stated that being the
core element in putative MCOs, Cu
2+ could stimulate the oxidation of Mn
2+ .
Investigation on kinetics of Mn
2+ oxidation by Zhang et al. (2002) explained that
at circumneutral pH, at a relatively low numbers of Mn-oxidizing bacteria
(Leptothrix discophora SS-1), biologically mediated Mn
2+ oxidation exceeded
abiotic oxidation. Interestingly, a recent study by El Gheriany et al. (2009)
remarked that Fe is essential for efficient Mn
2+ oxidation in Leptothrix discophora
SS-1.
3 Manganese Oxidation by Bacteria: Biogeochemical Aspects
59
presence of inhibitors. Similarly, Johnson and Kipphut (1988) showed by in situ
incubation technique, the rate of Mn
2+ oxidation is largely microbially mediated in
Toolik lake and is regulated by Mn
2+ concentration rather than temperature or
oxygen concentration. With more detailed experiment on mutants that lack the
ability to oxidize Mn
2+ , Caspi et al. (1998) stated that the Mn-oxidizing ability of
Pseudomonas putida MnB1 can be recovered by complementation of the mutation
in a c-type cytochrome biogenesis-defective mutant. In the kinetic studies on Mn
uptake and oxidation by Moy et al. (2003), the uptake of Mn
2+ by Rhizobium sp was
greater than the conversion of Mn
2+ to Mn oxides with significant production of
polysaccharides. They suggested that polysaccharides might be involved in the
uptake of Mn and in minimizing Mn oxide production. The study on redox
transformation of Mn in Antarctic lakes (Krishnan et al. 2009) showed that Co
could have a more profound role in Mn
2+ oxidation and Ni on Mn oxide reduction.
Although several studies report the oxidation of Mn
2+ by bacteria, the identity of
Mn-oxidizing bacteria remained undisclosed. Recently, Falamin and Pinevich
(2006) determined the phylogenetic position and phenotypic properties of Pseudomonas siderocapsa sp.nov. They suggested a mixotrophic mode of nutrition in the
strain and deposition of Mn oxides in their capsules rather than in outer membrane
as observed in other Pseudomonas species.
As an attempt to understand the Mn-oxidizing ability of Leptothrix discophora
SS-1 Adams and Ghiorse (1986) examined the ultrastructure of the strain by
electron microscopy. They could observe extracellular blebs in cells and proposed
it as vehicles for Mn-oxidizing protein. Manganese oxidation by sheathless strain
of Leptothrix discophora SS-1 belonging to b 1 subdivision of proteobacteria
(Boogerd and de Vrind 1987) in buffered medium at pH 7.5 showed the release
of Mn
2+ -oxidizing factors in the spent culture medium and was found associated
with MnO 2 aggregates. Meanwhile, Adams and Ghiorse (1987) isolated the Mn
2+ -
oxidizing protein from Leptothrix discophora SS-1 and characterized the extracellular Mn
2+ -oxidizing activity. The same authors in 1988 identified the oxidation states of Mn in the Mn oxide produced by Leptothrix discophora SS-1. They
could identify that the oxidation state of Mn in fresh samples exist as Mn
3+ and on
aging give rise to a mixture of Mn (III,IV) oxides in older samples. Later, study by
Corstjens et al. (1997) could identify that gene mofA is linked to Mn oxidation. In
addition, Nelson et al. (1999) showed that Mn oxides produced by SS-1 can
adsorb toxic metal lead. Moreover, Brouwers et al. (2000b) stated that being the
core element in putative MCOs, Cu
2+ could stimulate the oxidation of Mn
2+ .
Investigation on kinetics of Mn
2+ oxidation by Zhang et al. (2002) explained that
at circumneutral pH, at a relatively low numbers of Mn-oxidizing bacteria
(Leptothrix discophora SS-1), biologically mediated Mn
2+ oxidation exceeded
abiotic oxidation. Interestingly, a recent study by El Gheriany et al. (2009)
remarked that Fe is essential for efficient Mn
2+ oxidation in Leptothrix discophora
SS-1.
3 Manganese Oxidation by Bacteria: Biogeochemical Aspects
59