peptone at 18
C showed different toxic effects (Yang and Ehrlich 1976). Mn and Co
when tested alone had no effect on growth but their combination did. The combination of Co and Ni was more toxic than Co alone but less toxic than Ni alone. Cu was
comparatively more toxic than other metals. Its toxicity was slightly relieved by
Co or by the combination of Co and Mn, or Co, Mn, and Ni, but by no other metal
combinations tried. The mixtures of Mn and Ni and of Mn, Co, and Ni were more
toxic than their individual components. Likewise, Appanna et al. (1996) demonstrated the influence of Mn, Co, Cs, and Ni on the ability of Pseudomonas fluorescens
to adapt to and to decontaminate the multiple-metal environment. There the toxicity
of metals was comparatively lower in multiple-metal combinations than when
individual metals were tested. Mn was the least toxic followed by Cs, Co, and Ni.
Cs and Mn did not alter the cellular yield significantly; however, Ni and Co showed
marked inhibitory effect on bacterial growth.
A study on redox transformation of Mn in Antarctic lakes (Krishnan et al. 2009)
showed maximum stimulation of Mn oxidation (81 Æ 57 ppb d
À1 ) in Lister Hooded
(LH) strains with Mn–Co combination rather than combinations of Fe (37 Æ 16
ppb d
À1 ) and Ni (40 Æ 47 ppb d
À1 ), suggesting the role of Co in Mn oxidation.
Conversely, maximum stimulation of Mn reduction occurred in combinations
of the metals containing Ni. The rates were >50 ppb d
À1 with strain LH-11 and
>125 ppb d
À1 with strain LH-8 in combinations of Mn–Ni and Mn–Fe–Ni which
suggest the critical role of Ni in Mn reduction.
3.6 Manganese Oxidation by Marine Bacteria
The oxidation of Mn
2+ by marine bacteria is more versatile. Dick et al. (2008a)
have shown that Aurantimonas sp. Strain SI85-9A1, a marine a-proteobacterium,
contain genes for organoheterotrophy, methylotrophy, oxidation of sulfur and
carbon monoxide, the ability to grow over a wide range of oxygen concentrations,
and the complete Calvin cycle for carbon fixation. In an early study, Ehrlich (1963)
observed that bacteria in Mn nodules can enhance the adsorption of Mn
2+ from
seawater in the presence of peptone. He proposed that bacteria play a crucial role in
nodule development. Besides, Mn
2+ oxidation by cell-free extract from a Mn
nodule bacterium Arthrobacter 37 was found to be mediated by enzyme activity
(Ehrlich 1968). The rate of oxidation of free Mn
2+ by the enzyme depended on the
concentration of cell-free extract used. In another study on the effect of temperature
and pressure on Arthrobacter 37, Ehrlich (1971) demonstrated that at 5
C, temperature optimum for Mn
2+ oxidation increases with pressure and the effect of pressure
on cells can be counteracted by an appropriate increase in temperature. Further,
Arcuri and Ehrlich (1979) stated the involvement of cytochrome in Mn
2+ oxidation
by two marine bacteria. With the use of conventional electron transport chain, the
bacterium could derive useful energy from Mn
2+ oxidation by oxidative phosphorylation. By a detailed observation of bacteria that catalyze Mn
2+ oxidation, Ehrlich
(1980) postulated that two groups of Mn
2+ -oxidizing bacteria exist, one that acts on
54
P.P. Sujith and P.A. Loka Bharathi
C showed different toxic effects (Yang and Ehrlich 1976). Mn and Co
when tested alone had no effect on growth but their combination did. The combination of Co and Ni was more toxic than Co alone but less toxic than Ni alone. Cu was
comparatively more toxic than other metals. Its toxicity was slightly relieved by
Co or by the combination of Co and Mn, or Co, Mn, and Ni, but by no other metal
combinations tried. The mixtures of Mn and Ni and of Mn, Co, and Ni were more
toxic than their individual components. Likewise, Appanna et al. (1996) demonstrated the influence of Mn, Co, Cs, and Ni on the ability of Pseudomonas fluorescens
to adapt to and to decontaminate the multiple-metal environment. There the toxicity
of metals was comparatively lower in multiple-metal combinations than when
individual metals were tested. Mn was the least toxic followed by Cs, Co, and Ni.
Cs and Mn did not alter the cellular yield significantly; however, Ni and Co showed
marked inhibitory effect on bacterial growth.
A study on redox transformation of Mn in Antarctic lakes (Krishnan et al. 2009)
showed maximum stimulation of Mn oxidation (81 Æ 57 ppb d
À1 ) in Lister Hooded
(LH) strains with Mn–Co combination rather than combinations of Fe (37 Æ 16
ppb d
À1 ) and Ni (40 Æ 47 ppb d
À1 ), suggesting the role of Co in Mn oxidation.
Conversely, maximum stimulation of Mn reduction occurred in combinations
of the metals containing Ni. The rates were >50 ppb d
À1 with strain LH-11 and
>125 ppb d
À1 with strain LH-8 in combinations of Mn–Ni and Mn–Fe–Ni which
suggest the critical role of Ni in Mn reduction.
3.6 Manganese Oxidation by Marine Bacteria
The oxidation of Mn
2+ by marine bacteria is more versatile. Dick et al. (2008a)
have shown that Aurantimonas sp. Strain SI85-9A1, a marine a-proteobacterium,
contain genes for organoheterotrophy, methylotrophy, oxidation of sulfur and
carbon monoxide, the ability to grow over a wide range of oxygen concentrations,
and the complete Calvin cycle for carbon fixation. In an early study, Ehrlich (1963)
observed that bacteria in Mn nodules can enhance the adsorption of Mn
2+ from
seawater in the presence of peptone. He proposed that bacteria play a crucial role in
nodule development. Besides, Mn
2+ oxidation by cell-free extract from a Mn
nodule bacterium Arthrobacter 37 was found to be mediated by enzyme activity
(Ehrlich 1968). The rate of oxidation of free Mn
2+ by the enzyme depended on the
concentration of cell-free extract used. In another study on the effect of temperature
and pressure on Arthrobacter 37, Ehrlich (1971) demonstrated that at 5
C, temperature optimum for Mn
2+ oxidation increases with pressure and the effect of pressure
on cells can be counteracted by an appropriate increase in temperature. Further,
Arcuri and Ehrlich (1979) stated the involvement of cytochrome in Mn
2+ oxidation
by two marine bacteria. With the use of conventional electron transport chain, the
bacterium could derive useful energy from Mn
2+ oxidation by oxidative phosphorylation. By a detailed observation of bacteria that catalyze Mn
2+ oxidation, Ehrlich
(1980) postulated that two groups of Mn
2+ -oxidizing bacteria exist, one that acts on
54
P.P. Sujith and P.A. Loka Bharathi