3.2 Importance of Manganese
Manganese is a critical trace nutrient required for the growth and survival of many
living organisms. It is essential for oxygenic photosynthesis in cyanobacteria
(Yocum and Pecoraro 1999; Keren et al. 2002; Ogawa et al. 2002), redox reactions,
protection from toxic metals, UV light, predation or, viruses, scavenging of micronutrient trace metals, breakdown of natural organic matter into metabolizable
substrates, maintenance of an electron-acceptor reservoir for use in anaerobic
respiration, oxygen production, and protection against oxidative stress in bacteria
(Christianson 1997; Spiro et al. 2010). It is important for general metabolism,
carbohydrate metabolism, and for both anabolic and catabolic functions in anaerobiosis and aerobiosis (Crowley et al. 2000). It is a part of four metalloenzymes
manganese superoxide dismutase (MnSOD), mangani-catalase, arginase, and
O-phosphatases (Christianson 1997; Shi 2004). Mn
2+ containing O-phosphatases
are involved in controlling spore formation, stress-response, cell density during
stationary phase, carbon and nitrogen assimilation, vegetative growth, development
of fruiting bodies, and cell segregation (Shi 2004). Additionally, nonenzymatic Mn
2+
is crucial for the proper functioning of a variety of bacterial products, including
secreted antibiotics (Archibald 1986). It also contributes to the stabilization of
bacterial cell walls (Doyle 1989) and plays an important role in bacterial signal
transduction (Jakubovics and Jenkinson 2001). Mn
2+ is required for the stimulation
of poly-b-hydroxybutyrate oxidation in Sphaerotilus discophorous (Stokes
and Powers 1967) and exopolysaccharides (EPS) production in Rhizobium meliloti
JJ-1 (Appanna 1988). Being a part of an enzyme in glycolysis, Mn
2+ is required for
the activity of 3-phosphoglycerate mutase in several endospore-forming grampositive bacteria (Chander et al. 1998). Indirectly, Mn functions in controlling
nutrient availability in freshwater, most significantly by complexing with iron
(Kirchner and Grabowski 1972).
3.3 Biogeochemistry of Manganese
The geochemistry of Mn is a complex pattern of mutually exclusive chemical
reactions of oxidation and reduction (Kirchner and Grabowski 1972). The geochemical behavior of Mn differs in environment which shows gradation in oxygen
profile (Roitz et al. 2002). Mn occurs as highly soluble Mn
2+ in oxygen-deficient
settings and as insoluble oxyhydroxides under well-oxygenated conditions (Calvert
and Pedersen 1996). The concentration of soluble Mn in the environments varies
with change in redox condition and the group of microorganisms present. The
oxidation of Mn by microorganisms results in decrease in the dissolved Mn
2+
concentration of metal and increase in the particulate/higher oxidation states
(Mn
3+ and Mn
4+ ) of Mn (Ehrlich 1976, 1978). Redox transitions between soluble
Mn
2+ ions and insoluble Mn
3+ and Mn
4+ oxides form the backbone of aquatic
3 Manganese Oxidation by Bacteria: Biogeochemical Aspects
51
Manganese is a critical trace nutrient required for the growth and survival of many
living organisms. It is essential for oxygenic photosynthesis in cyanobacteria
(Yocum and Pecoraro 1999; Keren et al. 2002; Ogawa et al. 2002), redox reactions,
protection from toxic metals, UV light, predation or, viruses, scavenging of micronutrient trace metals, breakdown of natural organic matter into metabolizable
substrates, maintenance of an electron-acceptor reservoir for use in anaerobic
respiration, oxygen production, and protection against oxidative stress in bacteria
(Christianson 1997; Spiro et al. 2010). It is important for general metabolism,
carbohydrate metabolism, and for both anabolic and catabolic functions in anaerobiosis and aerobiosis (Crowley et al. 2000). It is a part of four metalloenzymes
manganese superoxide dismutase (MnSOD), mangani-catalase, arginase, and
O-phosphatases (Christianson 1997; Shi 2004). Mn
2+ containing O-phosphatases
are involved in controlling spore formation, stress-response, cell density during
stationary phase, carbon and nitrogen assimilation, vegetative growth, development
of fruiting bodies, and cell segregation (Shi 2004). Additionally, nonenzymatic Mn
2+
is crucial for the proper functioning of a variety of bacterial products, including
secreted antibiotics (Archibald 1986). It also contributes to the stabilization of
bacterial cell walls (Doyle 1989) and plays an important role in bacterial signal
transduction (Jakubovics and Jenkinson 2001). Mn
2+ is required for the stimulation
of poly-b-hydroxybutyrate oxidation in Sphaerotilus discophorous (Stokes
and Powers 1967) and exopolysaccharides (EPS) production in Rhizobium meliloti
JJ-1 (Appanna 1988). Being a part of an enzyme in glycolysis, Mn
2+ is required for
the activity of 3-phosphoglycerate mutase in several endospore-forming grampositive bacteria (Chander et al. 1998). Indirectly, Mn functions in controlling
nutrient availability in freshwater, most significantly by complexing with iron
(Kirchner and Grabowski 1972).
3.3 Biogeochemistry of Manganese
The geochemistry of Mn is a complex pattern of mutually exclusive chemical
reactions of oxidation and reduction (Kirchner and Grabowski 1972). The geochemical behavior of Mn differs in environment which shows gradation in oxygen
profile (Roitz et al. 2002). Mn occurs as highly soluble Mn
2+ in oxygen-deficient
settings and as insoluble oxyhydroxides under well-oxygenated conditions (Calvert
and Pedersen 1996). The concentration of soluble Mn in the environments varies
with change in redox condition and the group of microorganisms present. The
oxidation of Mn by microorganisms results in decrease in the dissolved Mn
2+
concentration of metal and increase in the particulate/higher oxidation states
(Mn
3+ and Mn
4+ ) of Mn (Ehrlich 1976, 1978). Redox transitions between soluble
Mn
2+ ions and insoluble Mn
3+ and Mn
4+ oxides form the backbone of aquatic
3 Manganese Oxidation by Bacteria: Biogeochemical Aspects
51