environment owing to its toxicity, even at a low concentration, and bioaccumulation
potential (Velea et al. 2009). Thus, SRB are an alternative method for sulfate and
heavy metal removal from wastewater, as well as oxidized sulfur compounds from
gas and water (Klonowska et al. 2008). Comparing the biological sulfate reduction
with conventional physical and chemical methods, it is an effective technique to treat
and reduce both heavy metals and sulfate from contaminated systems.
On the other hand, the toxicity of heavy metals in the microorganisms, including
SRB, deactivates enzymes because these react with the functional groups, provoking
the denaturation of proteins; also, there is a competition with essential cations. In
both cases, they can reduce bacterial metabolic activity or cause death. The concentration of the metal in solution is an important variable, since this depends on the
bacterial ability to immobilize the heavy metals. Several studies have determined the
capacity of tolerance towards the heavy metals on different cultures of SRB, since
their high metal tolerance and removal capabilities are particularly attractive in
heavy metal removal processes. The toxic concentration of heavy metals for SRB
can reach up to 100 mg/L but in a mixed culture of SRB for some metals is as
follows: Zn (25–40 mg/L), Pb (75–80 mg/L), Cu (4–20 mg/L), Cd ([4–20 mg/L), Ni
(10–20 mg/L) and Cr (60 mg/L) (Cabrera et al. 2006; Utgikar et al. 2002). In marine
SRB, a high tolerance level (500 μM) towards the most toxic metals, Hg(II) and Cd
(II), has been reported (El-Naggar 2009; Joo et al. 2015). The application of SRB as
an alternate technology on removal metal offers advantages such as high metal
removal at low pH, stable sludge, very low operation costs, and minimal energy
consumption (Ayangbenro et al. 2018).
13.5 Removing of Heavy Metal by Desulfovibrio
13.5.1 Desulfovibrio alaskensis as a Model of Removing of Metals
The species of the genus Desulfovibrio are the most studied in this field (Joo et al.
2015; Qian et al. 2016). The bacterial response to heavy metals depends on the
concentration and availability of metals, and on the response depends the
mechanisms of action towards the metals, which include precipitation, reduced
uptake, formation and sequestration of heavy metals in insoluble complexes, enzymatic oxidation or reduction to less toxic species, efflux from the cell, metabolic
bypass and repair (Gadd 2010; Haferburg and Kothe 2010). Such mechanisms can
be evaluated, particularly, in D. alaskensis strain 6SR showing high efficiency in the
removal of different metallic ions as Cd, Zn, Pb and Cr (López-Pérez et al. (2015);
Neria-González et al. 2011; Peña-Caballero et al. 2016).
Desulfovibrio alaskensis was isolated from a soured oil well in Prudhoe Bay,
Alaska, and its morphological description corresponds to gram-negative, mobile
curved bacilli with a single polar flagellum. The optimal growth conditions of the
bacterium in Postgate medium C correspond at a pH 7, 2.5% (w/v) NaCl and
temperature 37
C, using lactate as the main source of carbon and energy (Postgate
1984). Therefore, it is considered as a mesophilic and moderated halophilic
378
M. I. Neria-González and R. Aguilar-López
potential (Velea et al. 2009). Thus, SRB are an alternative method for sulfate and
heavy metal removal from wastewater, as well as oxidized sulfur compounds from
gas and water (Klonowska et al. 2008). Comparing the biological sulfate reduction
with conventional physical and chemical methods, it is an effective technique to treat
and reduce both heavy metals and sulfate from contaminated systems.
On the other hand, the toxicity of heavy metals in the microorganisms, including
SRB, deactivates enzymes because these react with the functional groups, provoking
the denaturation of proteins; also, there is a competition with essential cations. In
both cases, they can reduce bacterial metabolic activity or cause death. The concentration of the metal in solution is an important variable, since this depends on the
bacterial ability to immobilize the heavy metals. Several studies have determined the
capacity of tolerance towards the heavy metals on different cultures of SRB, since
their high metal tolerance and removal capabilities are particularly attractive in
heavy metal removal processes. The toxic concentration of heavy metals for SRB
can reach up to 100 mg/L but in a mixed culture of SRB for some metals is as
follows: Zn (25–40 mg/L), Pb (75–80 mg/L), Cu (4–20 mg/L), Cd ([4–20 mg/L), Ni
(10–20 mg/L) and Cr (60 mg/L) (Cabrera et al. 2006; Utgikar et al. 2002). In marine
SRB, a high tolerance level (500 μM) towards the most toxic metals, Hg(II) and Cd
(II), has been reported (El-Naggar 2009; Joo et al. 2015). The application of SRB as
an alternate technology on removal metal offers advantages such as high metal
removal at low pH, stable sludge, very low operation costs, and minimal energy
consumption (Ayangbenro et al. 2018).
13.5 Removing of Heavy Metal by Desulfovibrio
13.5.1 Desulfovibrio alaskensis as a Model of Removing of Metals
The species of the genus Desulfovibrio are the most studied in this field (Joo et al.
2015; Qian et al. 2016). The bacterial response to heavy metals depends on the
concentration and availability of metals, and on the response depends the
mechanisms of action towards the metals, which include precipitation, reduced
uptake, formation and sequestration of heavy metals in insoluble complexes, enzymatic oxidation or reduction to less toxic species, efflux from the cell, metabolic
bypass and repair (Gadd 2010; Haferburg and Kothe 2010). Such mechanisms can
be evaluated, particularly, in D. alaskensis strain 6SR showing high efficiency in the
removal of different metallic ions as Cd, Zn, Pb and Cr (López-Pérez et al. (2015);
Neria-González et al. 2011; Peña-Caballero et al. 2016).
Desulfovibrio alaskensis was isolated from a soured oil well in Prudhoe Bay,
Alaska, and its morphological description corresponds to gram-negative, mobile
curved bacilli with a single polar flagellum. The optimal growth conditions of the
bacterium in Postgate medium C correspond at a pH 7, 2.5% (w/v) NaCl and
temperature 37
C, using lactate as the main source of carbon and energy (Postgate
1984). Therefore, it is considered as a mesophilic and moderated halophilic
378
M. I. Neria-González and R. Aguilar-López