Specifically, the species of the genus Desulfovibrio have been the most studied
for metal removal with a high efficiency, where the main mechanism is the
precipitation of metal sulfides among others. Desulfovibrio alaskensis 6SR
exhibits a high metallic resistance with respect to other sulfate-reducing bacteria,
including other microorganisms; since it shows strong resistance to Cr(VI), Cd
(II), Pb(II) and Zn(II), some of these are considered as extremely toxic to biota.
Desulfovibrio alaskensis strain 6SR is capable to remove more of the 98% Cr
(VI) Cd(II), Pb(II) and Zn(II) in solution. The main mechanism of removal is the
precipitation of the corresponding metallic sulfides, followed by adsorption of
these by the produced EPS, and transmission electron micrographs show a slight
metal accumulation at the intracellular level and periplasmic space. Also, the
chromium reducing for the hydrogen sulfide has been analyzed by the sulfate
reduction in independent reactors, as well as in culture per batch of D. alaskensis.
The results indicate that the bacterium is able to grow up to a concentration of
18 mg/L of Cr(VI), and contrary to D. vulgaris, the reduction of sulfate does not
interrupt at any time of the chromium reducing. Finally, a molecular analysis with
respect to cadmium and chromium resistance mechanisms demonstrated the
presence of cadA and chrA genes. Both genes are induced by Cd, Zn, Pb and
Cr; the codified proteins by these genes are involucre to abate the oxidative stress
provoked by heavy metal non-essentials.
Keywords
Heavy metals · Sulfate-reducing bacteria · Wastewater · Microbial reduction ·
Desulfovibrio alaskensis
13.1 Introduction
Ever since that the human is done sedentary, the usage of metals was incrementing;
now they are used for everything, from construction to improve our health. Some
metals are also necessary for the vital processes of any organisms. But where do we
obtain the metals? In answer to this question, the Earth’s crust is the main source of
metals. So, gold, silver, platinum and others are found as the uncombined elements
or native or free state, known as non-reactive metals too. In general, most metals are
found combined with other elements to form compounds; on both cases, these are in
rocks named ores. Most metals are extracted from ores by different extraction
methods that depend upon the metal’s position in the reactivity series. In principle,
any metal could be extracted from its compound using electrolysis, but the using of
large amounts of electrical energy results expensive, and other types of extraction
methods are required, but this is another story. The fact is that the high demand of
metals for various anthropogenic activities as the manufacture of steel, foundries,
electroplating, auto parts, fuel production, manufacture of electronic devices, manufacture of agrochemicals and manufacture of batteries, among others, is the main
source of metallic contamination (Haferburg and Kothe 2010). The metals are
368
M. I. Neria-González and R. Aguilar-López
for metal removal with a high efficiency, where the main mechanism is the
precipitation of metal sulfides among others. Desulfovibrio alaskensis 6SR
exhibits a high metallic resistance with respect to other sulfate-reducing bacteria,
including other microorganisms; since it shows strong resistance to Cr(VI), Cd
(II), Pb(II) and Zn(II), some of these are considered as extremely toxic to biota.
Desulfovibrio alaskensis strain 6SR is capable to remove more of the 98% Cr
(VI) Cd(II), Pb(II) and Zn(II) in solution. The main mechanism of removal is the
precipitation of the corresponding metallic sulfides, followed by adsorption of
these by the produced EPS, and transmission electron micrographs show a slight
metal accumulation at the intracellular level and periplasmic space. Also, the
chromium reducing for the hydrogen sulfide has been analyzed by the sulfate
reduction in independent reactors, as well as in culture per batch of D. alaskensis.
The results indicate that the bacterium is able to grow up to a concentration of
18 mg/L of Cr(VI), and contrary to D. vulgaris, the reduction of sulfate does not
interrupt at any time of the chromium reducing. Finally, a molecular analysis with
respect to cadmium and chromium resistance mechanisms demonstrated the
presence of cadA and chrA genes. Both genes are induced by Cd, Zn, Pb and
Cr; the codified proteins by these genes are involucre to abate the oxidative stress
provoked by heavy metal non-essentials.
Keywords
Heavy metals · Sulfate-reducing bacteria · Wastewater · Microbial reduction ·
Desulfovibrio alaskensis
13.1 Introduction
Ever since that the human is done sedentary, the usage of metals was incrementing;
now they are used for everything, from construction to improve our health. Some
metals are also necessary for the vital processes of any organisms. But where do we
obtain the metals? In answer to this question, the Earth’s crust is the main source of
metals. So, gold, silver, platinum and others are found as the uncombined elements
or native or free state, known as non-reactive metals too. In general, most metals are
found combined with other elements to form compounds; on both cases, these are in
rocks named ores. Most metals are extracted from ores by different extraction
methods that depend upon the metal’s position in the reactivity series. In principle,
any metal could be extracted from its compound using electrolysis, but the using of
large amounts of electrical energy results expensive, and other types of extraction
methods are required, but this is another story. The fact is that the high demand of
metals for various anthropogenic activities as the manufacture of steel, foundries,
electroplating, auto parts, fuel production, manufacture of electronic devices, manufacture of agrochemicals and manufacture of batteries, among others, is the main
source of metallic contamination (Haferburg and Kothe 2010). The metals are
368
M. I. Neria-González and R. Aguilar-López