Recent advancement in the understanding of microbial Mn oxidation provides
insight into the mechanisms of metal oxidation and the processes involved. This
oxidation proceeds at rates up to five orders of magnitude greater than abiotic
oxidation (Tebo et al. 1997). The Mn oxides produced by microorganisms are
abundant environmental nanoparticles, they have great importance in biotechnology for the removal of heavy metals from aqueous matrices and oxidation of
organic micropollutants in wastewater treatment plants (Villalobos et al. 2005b).
The higher specific surface area of negatively charged biogenic Mn oxides than
synthetic d-MnO 2 and commercially available pyrolusite allow greater sorption of
positively charged heavy metals in solution (Hennebel et al. 2009). The bacterial
spores from a potent Mn-oxidizing bacteria Bacillus sp. SG-1 have found extensive
capacity for actively binding and oxidizing Mn and passively binding other metals.
Likewise, Mn-oxidizing protein from Pseudomonas putida Strains MnB1 and GB-1
as well as sheath of Leptothrix discophora is found to have similar function (Francis
and Tebo 1999). It was observed by Nelson et al. (2002); Villalobos et al. (2005a)
that Mn oxides produced by Leptothrix discophora SS-1 and Pseudomonas putida
MnB1 can adsorb five times more Pb per mole of Mn than abiotic Mn(IV) (hydr)
oxide and 500–5,000 times more than pyrolusite oxides, thus stimulating interest in
the development of Mn oxides for use in bioremediation. Likewise, Toner et al.
(2006) observed a tenfold higher capacity for biogenic Mn oxides in adsorbing
Zn than chemically synthesized Mn oxides, and Murray and Tebo (2007) detected
seven times higher adsorption of Cr in biogenic Mn oxides produced by Bacillus sp.
SG-1 than synthetic d-MnO 2 . The utilization of these microorganisms in concentrating metal ions from effluents will have intense application in biotechnology for
treatment of wastewaters and metal-containing effluents.
It has also been observed recently that biogenic Mn oxides can oxidize 17aEthinylestradiol, a potent endocrine-disrupting recalcitrant, and reduce its estrogenic activity to 81.7% (de Rudder et al. 2004). In another recent observation,
Forrez et al. (2010) have shown that biogenic Mn oxides can oxidize diclofenac, a
nonsteroidal anti-inflammatory drug and can reduce its lethal concentration and
toxicity. Similar observations made for triclosan (Zhang and Huang 2003) and
ciprofloxacin (Zhang and Huang 2005) with biogenic Mn oxides suggest that
biogenic manganese oxide can be a promising polishing technique for sewage
treatment plant effluents.
3.12 Conclusion
The current understanding about bacterial Mn oxidation comprises the participation
of MCOs, but their direct link to oxidation is emphasized only in Bacillus SG-1
and not in other organisms like Pseudomonas putida MnB1, GB1, Leptothrix
discophora SS1, or Pedomicrobium sp. ACM3067. The various regulatory
mechanisms and transport systems for Mn uptake in bacterial cells are studied but
the role of metalloproteins in Mn oxidation or how the proteins select the right
66
P.P. Sujith and P.A. Loka Bharathi
insight into the mechanisms of metal oxidation and the processes involved. This
oxidation proceeds at rates up to five orders of magnitude greater than abiotic
oxidation (Tebo et al. 1997). The Mn oxides produced by microorganisms are
abundant environmental nanoparticles, they have great importance in biotechnology for the removal of heavy metals from aqueous matrices and oxidation of
organic micropollutants in wastewater treatment plants (Villalobos et al. 2005b).
The higher specific surface area of negatively charged biogenic Mn oxides than
synthetic d-MnO 2 and commercially available pyrolusite allow greater sorption of
positively charged heavy metals in solution (Hennebel et al. 2009). The bacterial
spores from a potent Mn-oxidizing bacteria Bacillus sp. SG-1 have found extensive
capacity for actively binding and oxidizing Mn and passively binding other metals.
Likewise, Mn-oxidizing protein from Pseudomonas putida Strains MnB1 and GB-1
as well as sheath of Leptothrix discophora is found to have similar function (Francis
and Tebo 1999). It was observed by Nelson et al. (2002); Villalobos et al. (2005a)
that Mn oxides produced by Leptothrix discophora SS-1 and Pseudomonas putida
MnB1 can adsorb five times more Pb per mole of Mn than abiotic Mn(IV) (hydr)
oxide and 500–5,000 times more than pyrolusite oxides, thus stimulating interest in
the development of Mn oxides for use in bioremediation. Likewise, Toner et al.
(2006) observed a tenfold higher capacity for biogenic Mn oxides in adsorbing
Zn than chemically synthesized Mn oxides, and Murray and Tebo (2007) detected
seven times higher adsorption of Cr in biogenic Mn oxides produced by Bacillus sp.
SG-1 than synthetic d-MnO 2 . The utilization of these microorganisms in concentrating metal ions from effluents will have intense application in biotechnology for
treatment of wastewaters and metal-containing effluents.
It has also been observed recently that biogenic Mn oxides can oxidize 17aEthinylestradiol, a potent endocrine-disrupting recalcitrant, and reduce its estrogenic activity to 81.7% (de Rudder et al. 2004). In another recent observation,
Forrez et al. (2010) have shown that biogenic Mn oxides can oxidize diclofenac, a
nonsteroidal anti-inflammatory drug and can reduce its lethal concentration and
toxicity. Similar observations made for triclosan (Zhang and Huang 2003) and
ciprofloxacin (Zhang and Huang 2005) with biogenic Mn oxides suggest that
biogenic manganese oxide can be a promising polishing technique for sewage
treatment plant effluents.
3.12 Conclusion
The current understanding about bacterial Mn oxidation comprises the participation
of MCOs, but their direct link to oxidation is emphasized only in Bacillus SG-1
and not in other organisms like Pseudomonas putida MnB1, GB1, Leptothrix
discophora SS1, or Pedomicrobium sp. ACM3067. The various regulatory
mechanisms and transport systems for Mn uptake in bacterial cells are studied but
the role of metalloproteins in Mn oxidation or how the proteins select the right
66
P.P. Sujith and P.A. Loka Bharathi