mofA operon. At the same time, Siering and Ghiorse (1997b) by variable stringency
hybridization analysis using digoxigenin-labelled mofA probe of Leptothrix
discophorora SS-1 showed that Mn-oxidation genes of other Leptothrix spp were
closely related to one another but were not homologous to the unidentified presumptive Mn oxidation genes from other genera. In the meanwhile, Siering and
Ghiorse (1997a) could detect sheathed bacteria (Leptothrix spp) in environmental
samples based on their designed 16S rRNA-targeted specific probes and proposed
its applications in further research.
The other common bacterial genera known for Mn
2+ oxidation are Pseudomonas
putida Strains MnB1 and GB-1. There are several reports (Caspi et al. 1996; Caspi
et al. 1998; Brouwers et al. 1999; de Vrind et al. 2003) that describe the Mnoxidizing ability of these strains. But only few (Brouwers et al. 1999, 2000a)
attempts have been made to understand the genetic mechanisms involved in Mn
2+
oxidation. They could identify by molecular analysis that gene cumA (copper
protein involved in Mn oxidation) participates with MCOs in Mn
2+ oxidation and
cumB for optimal growth. Later, Francis and Tebo (2001) surprisingly observed
highly conserved cumA gene sequences in non-Mn-oxidizing Pseudomonas strains.
Based on the results, they suggested that cumA gene may not be expressed or that it
may not be the only gene to confer the ability to oxidize Mn
2+ . Conversely, they
could exert an alternative function in these organisms and the gene could occur in
phylogenetically diverse Pseudomonas strains.
Pedomicrobium sp. ACM3067 another aquatic bacteria could oxidize Mn
2+ in
close association with an extracellular matrix of acidic polysaccharides or polymer
(Ghiorse and Hirsch 1979). Further, understanding about the mechanism involved
in Mn
2+ oxidation (Larsen et al. 1999) showed that Mn
2+ oxidation is catalyzed by a
copper-dependent enzyme in Pedomicrobium sp. ACM3067. Recent study by
Ridge et al. (2007) provided evidence that moxA gene encoding a MCO homolog
is essential for both Mn
2+ oxidation and laccase-like activity in Pedomicrobium sp.
ACM3067.
Mn-oxidizing genus Hypomicrobium is less probed at genetic level. Only one
study by Layton et al. (2000) recorded the abundance of Hypomicrobium
populations in activated sludge based on 16S rRNA analysis. About 5% of 16S
rRNA in activated sludge corresponded to Hypomicrobium sp. Gregory and Staley
(1982) showed experimental evidence that Mn
2+ -oxidizing ability in the bacterial
isolates was lost when maintained in the absence of the metal in the laboratory.
They hypothesized that Mn oxidation may be directly related to the presence of
plasmids.
3.9 Manganese Oxidation: A Proteomic Perspective
Metal ion efflux systems are central to cellular physiology. The uptake of Mn in
bacteria occurs through (1) P-type ATPase (MntA) (Hao et al. 1999), (2) metal
binding protein-dependent ABC transport system: Group PsaA, (3) pH-dependent
3 Manganese Oxidation by Bacteria: Biogeochemical Aspects
61
hybridization analysis using digoxigenin-labelled mofA probe of Leptothrix
discophorora SS-1 showed that Mn-oxidation genes of other Leptothrix spp were
closely related to one another but were not homologous to the unidentified presumptive Mn oxidation genes from other genera. In the meanwhile, Siering and
Ghiorse (1997a) could detect sheathed bacteria (Leptothrix spp) in environmental
samples based on their designed 16S rRNA-targeted specific probes and proposed
its applications in further research.
The other common bacterial genera known for Mn
2+ oxidation are Pseudomonas
putida Strains MnB1 and GB-1. There are several reports (Caspi et al. 1996; Caspi
et al. 1998; Brouwers et al. 1999; de Vrind et al. 2003) that describe the Mnoxidizing ability of these strains. But only few (Brouwers et al. 1999, 2000a)
attempts have been made to understand the genetic mechanisms involved in Mn
2+
oxidation. They could identify by molecular analysis that gene cumA (copper
protein involved in Mn oxidation) participates with MCOs in Mn
2+ oxidation and
cumB for optimal growth. Later, Francis and Tebo (2001) surprisingly observed
highly conserved cumA gene sequences in non-Mn-oxidizing Pseudomonas strains.
Based on the results, they suggested that cumA gene may not be expressed or that it
may not be the only gene to confer the ability to oxidize Mn
2+ . Conversely, they
could exert an alternative function in these organisms and the gene could occur in
phylogenetically diverse Pseudomonas strains.
Pedomicrobium sp. ACM3067 another aquatic bacteria could oxidize Mn
2+ in
close association with an extracellular matrix of acidic polysaccharides or polymer
(Ghiorse and Hirsch 1979). Further, understanding about the mechanism involved
in Mn
2+ oxidation (Larsen et al. 1999) showed that Mn
2+ oxidation is catalyzed by a
copper-dependent enzyme in Pedomicrobium sp. ACM3067. Recent study by
Ridge et al. (2007) provided evidence that moxA gene encoding a MCO homolog
is essential for both Mn
2+ oxidation and laccase-like activity in Pedomicrobium sp.
ACM3067.
Mn-oxidizing genus Hypomicrobium is less probed at genetic level. Only one
study by Layton et al. (2000) recorded the abundance of Hypomicrobium
populations in activated sludge based on 16S rRNA analysis. About 5% of 16S
rRNA in activated sludge corresponded to Hypomicrobium sp. Gregory and Staley
(1982) showed experimental evidence that Mn
2+ -oxidizing ability in the bacterial
isolates was lost when maintained in the absence of the metal in the laboratory.
They hypothesized that Mn oxidation may be directly related to the presence of
plasmids.
3.9 Manganese Oxidation: A Proteomic Perspective
Metal ion efflux systems are central to cellular physiology. The uptake of Mn in
bacteria occurs through (1) P-type ATPase (MntA) (Hao et al. 1999), (2) metal
binding protein-dependent ABC transport system: Group PsaA, (3) pH-dependent
3 Manganese Oxidation by Bacteria: Biogeochemical Aspects
61