(Ghiorse and Hirsch 1979; Sly et al. 1990). The mechanism of Mn
2+ oxidation was
found to involve a two-step process composed of rapid binding of Mn
2+ to EPS
followed by the oxidation of Mn
2+ by an unknown factor (Ghiorse and Hirsch
1979). Incidentally, they could identify the unusual factor, perhaps a protein
responsible for Mn
2+ oxidation associated with the polymer that could not be
completely inhibited by glutaraldehyde, HgCl 2 , or heat. Further findings using
inhibitors and cellular fractionation methods (Larsen et al. 1999) showed that
heat treatment of cells could enhance Mn
2+ binding but abolish Mn-oxidizing
activity. They could restore the activity of the enzyme upon the addition of Cu in
the medium and suggested that Cu-dependent enzyme MCOs catalyze the Mn
2+
oxidation in Pedomicrobium ACM 3067.
Jaquet et al. (1982) indicated that Metallogenium plays a key role in Mn cycling
in Lake Leman. In contrast, Maki et al. (1987) using
54 Mn tracer could not find
any significant difference between poisoned and non-oxygen controls in the
biological Mn
2+ oxidation and the number of Metallogenium morphotypes in
Lake Washington. They suggested that Metallogenium plays only a weak role in
Mn
2+ oxidation in Lake Washington. In a discussion on the retention of Mn in the
Wahnbach reservoir by bacteria, Herschel and Clasen (1998) state that Metallogenium personatum could be a propelling force behind microbially catalyzed
transformation of Mn in the reservoir. They explained that increase in dissolved
oxygen level in deep water is conducive for Mn
2+ oxidation. In some earlier
observations, Tyler and Marshall (1967) and Tyler (1970) addressed the widespread
occurrence of stalked, budding bacteria Hyphomicrobium belonging to aproteobacteria in Mn deposits and suggested that some Hyphomicrobia could
preferentially oxidize Mn over Fe in hydroelectric pipelines.
In an interesting observation, Uren and Leeper (1978) stated that microbial
oxidation of Mn
2+ in soil could occur at low oxygen pressures provided CO 2
supplied is adequate. With Arthrobacter sp from soil, Bromfield and David
(1976) had also showed that oxides of Mn could rapidly adsorb manganous ions
from aqueous solutions but not in the case of abiotic control. In a kinetic study with
cell free extracts of two bacterial isolates Pseudomonas III and Citrobacter freundii
belonging to g-proteobacteria, Douka (1980) identified that the rate of Mn
2+
oxidation increased with its concentration, suggesting a strong affinity between
the oxidizing system and Mn. Conversely, Chapnick et al. (1982) could show that
Mn
2+ removal from water column and oxidation in Lake Oneida during summer
months are mediated by metabolically active Mn-oxidizing bacteria. They also
showed that particles in lake water when removed by filtration or killed by ethanol
treatment inhibit the activity. Besides, Gregory and Staley (1982) suggested that
plasmids may be directly involved in Mn oxidation by providing essential gene
products or may act indirectly by altering the microenvironment in a way as to
make the chemical oxidation of Mn
2+ favorable. Using in situ dialysis technique,
Kepkay (1985) showed that Mn precipitation in soil could be a microbially
mediated process causing a fivefold enhancement of abiotic process such as
adsorption. Likewise, Vojak et al. (1985) stated that biological process could be
responsible for the change in oxidation state of Mn
2+ to Mn
4+ . The rates of Mn
2+
58
P.P. Sujith and P.A. Loka Bharathi
2+ oxidation was
found to involve a two-step process composed of rapid binding of Mn
2+ to EPS
followed by the oxidation of Mn
2+ by an unknown factor (Ghiorse and Hirsch
1979). Incidentally, they could identify the unusual factor, perhaps a protein
responsible for Mn
2+ oxidation associated with the polymer that could not be
completely inhibited by glutaraldehyde, HgCl 2 , or heat. Further findings using
inhibitors and cellular fractionation methods (Larsen et al. 1999) showed that
heat treatment of cells could enhance Mn
2+ binding but abolish Mn-oxidizing
activity. They could restore the activity of the enzyme upon the addition of Cu in
the medium and suggested that Cu-dependent enzyme MCOs catalyze the Mn
2+
oxidation in Pedomicrobium ACM 3067.
Jaquet et al. (1982) indicated that Metallogenium plays a key role in Mn cycling
in Lake Leman. In contrast, Maki et al. (1987) using
54 Mn tracer could not find
any significant difference between poisoned and non-oxygen controls in the
biological Mn
2+ oxidation and the number of Metallogenium morphotypes in
Lake Washington. They suggested that Metallogenium plays only a weak role in
Mn
2+ oxidation in Lake Washington. In a discussion on the retention of Mn in the
Wahnbach reservoir by bacteria, Herschel and Clasen (1998) state that Metallogenium personatum could be a propelling force behind microbially catalyzed
transformation of Mn in the reservoir. They explained that increase in dissolved
oxygen level in deep water is conducive for Mn
2+ oxidation. In some earlier
observations, Tyler and Marshall (1967) and Tyler (1970) addressed the widespread
occurrence of stalked, budding bacteria Hyphomicrobium belonging to aproteobacteria in Mn deposits and suggested that some Hyphomicrobia could
preferentially oxidize Mn over Fe in hydroelectric pipelines.
In an interesting observation, Uren and Leeper (1978) stated that microbial
oxidation of Mn
2+ in soil could occur at low oxygen pressures provided CO 2
supplied is adequate. With Arthrobacter sp from soil, Bromfield and David
(1976) had also showed that oxides of Mn could rapidly adsorb manganous ions
from aqueous solutions but not in the case of abiotic control. In a kinetic study with
cell free extracts of two bacterial isolates Pseudomonas III and Citrobacter freundii
belonging to g-proteobacteria, Douka (1980) identified that the rate of Mn
2+
oxidation increased with its concentration, suggesting a strong affinity between
the oxidizing system and Mn. Conversely, Chapnick et al. (1982) could show that
Mn
2+ removal from water column and oxidation in Lake Oneida during summer
months are mediated by metabolically active Mn-oxidizing bacteria. They also
showed that particles in lake water when removed by filtration or killed by ethanol
treatment inhibit the activity. Besides, Gregory and Staley (1982) suggested that
plasmids may be directly involved in Mn oxidation by providing essential gene
products or may act indirectly by altering the microenvironment in a way as to
make the chemical oxidation of Mn
2+ favorable. Using in situ dialysis technique,
Kepkay (1985) showed that Mn precipitation in soil could be a microbially
mediated process causing a fivefold enhancement of abiotic process such as
adsorption. Likewise, Vojak et al. (1985) stated that biological process could be
responsible for the change in oxidation state of Mn
2+ to Mn
4+ . The rates of Mn
2+
58
P.P. Sujith and P.A. Loka Bharathi