metal ions and their removal to the surface of the cell, and intracellular sequestration
in the form of intracytoplasmic inclusions. Binding of cations to the surface of the
cell has become one of the most attractive biotransformation models. Metals
possessing an electron configuration containing 10–12 layers of electrons are often
toxic to organisms at relatively low concentrations. In this group are Hg
2+ , Ag
+ , Pb
2
+
, Cd
2+ , and Zn
2+ . Metal/MO interactions play a role in numerous biotechnologies,
such as bioremediation, biomineralization, bioleaching, and microbial corrosion.
It is intended to use bacterial strains in pure cultures or in consortia capable of
mobilizing/immobilizing metal ions. Remediation of metals often involves five
approaches: isolation, immobilization, mobilization, physical separation, and extraction. Immobilization and mobilization involve bacterial bioremediation processes.
Immobilization is a technique for reducing the mobility of the contaminant by
altering its physicochemical properties.
MOs are used, and the process can be carried out in situ or ex situ. MOs can
mobilize metals by autotrophic or heterotrophic leaching by chelation by metabolites
and siderophores by methylation and redox transformations (Das et al. 2007).
Heterotrophic leaching takes place when the MO acidizes the environment through
proton efflux (proton driving force), resulting in the release of metal cations.
Autotrophic leaching occurs when the acidophilic bacteria obtain the energy
required to fix CO 2 by oxidation of reduced Fe inorganic compounds (Fe
2+ ) or
reduced S compounds. Siderophores are specific Fe
3+ ligands but can bind other
metals, such as Mn, Mg, and Cr. Methylation involves the methyl group that is
enzymatically transferred to a metal, forming a number of different metalloids.
Redox transformations allow MOs to mobilize metals, metalloids, and organometallic compounds. There are many metal mobilization techniques, the technology being
chosen depending on the physical and chemical characteristics of the metal
(Wu et al. 2018).
4.5.3 The Importance of Microorganisms with Depollution
Potential and High Bioremediation Potential
Bacteria belonging to the genus Pseudomonas have a chemoorganoheterotrophic
nutrition and are polar flame lates of bacilli, with strict aerobic breathing, having
molecular oxygen as the ultimate acceptor of electrons in the respiratory chain. They
do not grow to pH below 4.5. They produce siderophores – chelating compounds
that bind and immobilize Fe but also other metal ions: Al, Cr, Zn, Cu, Mn, Pb,
Cd, etc.
The main siderophore produced by P. putida, as well as other species of the same
genus (P. aeruginosa, P. fluorescens, P. chlororaphis), also very useful in the
processes of decontamination of polluted soils, is Pyoverdine. The action of
siderophores is of great ecological importance due to the insolubility of its
compounds. Siderophores bind Fe
3+ compounds to form complexes that are
transported inside cells where they can be used for respiration by anaerobic MOs
such as Fe-reducing bacteria (Geobacter bremensis, G. pelophilus,
96
M. Butu et al.
in the form of intracytoplasmic inclusions. Binding of cations to the surface of the
cell has become one of the most attractive biotransformation models. Metals
possessing an electron configuration containing 10–12 layers of electrons are often
toxic to organisms at relatively low concentrations. In this group are Hg
2+ , Ag
+ , Pb
2
+
, Cd
2+ , and Zn
2+ . Metal/MO interactions play a role in numerous biotechnologies,
such as bioremediation, biomineralization, bioleaching, and microbial corrosion.
It is intended to use bacterial strains in pure cultures or in consortia capable of
mobilizing/immobilizing metal ions. Remediation of metals often involves five
approaches: isolation, immobilization, mobilization, physical separation, and extraction. Immobilization and mobilization involve bacterial bioremediation processes.
Immobilization is a technique for reducing the mobility of the contaminant by
altering its physicochemical properties.
MOs are used, and the process can be carried out in situ or ex situ. MOs can
mobilize metals by autotrophic or heterotrophic leaching by chelation by metabolites
and siderophores by methylation and redox transformations (Das et al. 2007).
Heterotrophic leaching takes place when the MO acidizes the environment through
proton efflux (proton driving force), resulting in the release of metal cations.
Autotrophic leaching occurs when the acidophilic bacteria obtain the energy
required to fix CO 2 by oxidation of reduced Fe inorganic compounds (Fe
2+ ) or
reduced S compounds. Siderophores are specific Fe
3+ ligands but can bind other
metals, such as Mn, Mg, and Cr. Methylation involves the methyl group that is
enzymatically transferred to a metal, forming a number of different metalloids.
Redox transformations allow MOs to mobilize metals, metalloids, and organometallic compounds. There are many metal mobilization techniques, the technology being
chosen depending on the physical and chemical characteristics of the metal
(Wu et al. 2018).
4.5.3 The Importance of Microorganisms with Depollution
Potential and High Bioremediation Potential
Bacteria belonging to the genus Pseudomonas have a chemoorganoheterotrophic
nutrition and are polar flame lates of bacilli, with strict aerobic breathing, having
molecular oxygen as the ultimate acceptor of electrons in the respiratory chain. They
do not grow to pH below 4.5. They produce siderophores – chelating compounds
that bind and immobilize Fe but also other metal ions: Al, Cr, Zn, Cu, Mn, Pb,
Cd, etc.
The main siderophore produced by P. putida, as well as other species of the same
genus (P. aeruginosa, P. fluorescens, P. chlororaphis), also very useful in the
processes of decontamination of polluted soils, is Pyoverdine. The action of
siderophores is of great ecological importance due to the insolubility of its
compounds. Siderophores bind Fe
3+ compounds to form complexes that are
transported inside cells where they can be used for respiration by anaerobic MOs
such as Fe-reducing bacteria (Geobacter bremensis, G. pelophilus,
96
M. Butu et al.