2007). Bacteria of the genera Bacillus and Streptomyces and yeasts possess the
capacity of adsorbing high amounts of metals from solution, due to the adsorption of
the metallic ions by ionizable groups of the cell surface constituents, such as
peptidoglycan, cellular membrane and capsule (carboxyl, amino, phosphate and
hydroxyl groups) (Das et al. 2008; Ahluwalia and Goyal 2007). Macroalgae and
alginate derivatives exhibit high affinity towards many metal ions. The major
advantages of biosorption over conventional methods include low cost, high efficiency, minimization of chemical or biological sludge, the regeneration of
biosorbents and possibility of metal recovery chemical or biological sludge
(Gavrilescu 2004).
Heavy metal ions are also adsorbed by extracellular biopolymers or
exopolysaccharide (EPS) produced by bacteria, which form the bacterial capsules
and other bacterial covers. The carboxyl groups of polysaccharides hold back and
accumulate metal ions. Extracellular biopolymers of Enterobacter cloacae,
Marinobacter sp., Klebsiella aerogenes and Acinetobacter sp. have shown metallic
accumulation. However, a considerable accumulation of ions of copper, lead and
zinc was demonstrated on Pseudomonas aeruginosa cell biofilms. EPS acts as a
barrier of protecting bacterial cells inside of biofilm of the toxicity of metal ions
(Ianieva 2009).
The accumulation of intracellular metal ions responds to changes in cell membrane permeability. Thus, some metallic ions can enter the cell via the systems
responsible for the uptake of essential elements, as in the case of Ralstonia
metallidurans, the ions of cadmium, zinc, cobalt, nickel and manganese enter at
the cell using systems of magnesium transport. Another example is chromate using
sulfate transport system (Ianieva 2009; Gadd 2010). The passage of metal ions into
the cell causes response detoxification of toxic metals, which is based on the
expression of proteins capable of being complex with metallic ion. These metallic
complexes are out from the cell, and these accumulate in cell membrane surface or in
the periplasmic space or are deposited in internal vacuoles called inclusion bodies.
These are called resistance mechanisms and are associated with metallothioneins and
metallohistins, molecules of intracellular storage and detoxification able to bind
heavy metals (Haferburg and Kothe 2010; Thakare et al. 2021). This may provide
an excellent source of applicable mechanisms in environment biotechnological
decontamination.
13.3.2 Precipitation
In the precipitation produced chemically stable forms of metal and only use to
reducible metals. Metabolic activity of the microorganisms contributes to the removing indirect or direct of metals, e.g. metal precipitation by secreted phosphate
generated from polyphosphate hydrolysis. In this context, the precipitation by
phosphates and sulfides has been investigated due to the low solubility of their
metal compounds. This mechanism is suggested to remove metals and actinides
from wastewater. Therefore, the selective precipitation of metals with the hydrogen
sulfide produced by sulfate-reducing bacteria (SRB) is the most studded (Joo et al.
372
M. I. Neria-González and R. Aguilar-López
capacity of adsorbing high amounts of metals from solution, due to the adsorption of
the metallic ions by ionizable groups of the cell surface constituents, such as
peptidoglycan, cellular membrane and capsule (carboxyl, amino, phosphate and
hydroxyl groups) (Das et al. 2008; Ahluwalia and Goyal 2007). Macroalgae and
alginate derivatives exhibit high affinity towards many metal ions. The major
advantages of biosorption over conventional methods include low cost, high efficiency, minimization of chemical or biological sludge, the regeneration of
biosorbents and possibility of metal recovery chemical or biological sludge
(Gavrilescu 2004).
Heavy metal ions are also adsorbed by extracellular biopolymers or
exopolysaccharide (EPS) produced by bacteria, which form the bacterial capsules
and other bacterial covers. The carboxyl groups of polysaccharides hold back and
accumulate metal ions. Extracellular biopolymers of Enterobacter cloacae,
Marinobacter sp., Klebsiella aerogenes and Acinetobacter sp. have shown metallic
accumulation. However, a considerable accumulation of ions of copper, lead and
zinc was demonstrated on Pseudomonas aeruginosa cell biofilms. EPS acts as a
barrier of protecting bacterial cells inside of biofilm of the toxicity of metal ions
(Ianieva 2009).
The accumulation of intracellular metal ions responds to changes in cell membrane permeability. Thus, some metallic ions can enter the cell via the systems
responsible for the uptake of essential elements, as in the case of Ralstonia
metallidurans, the ions of cadmium, zinc, cobalt, nickel and manganese enter at
the cell using systems of magnesium transport. Another example is chromate using
sulfate transport system (Ianieva 2009; Gadd 2010). The passage of metal ions into
the cell causes response detoxification of toxic metals, which is based on the
expression of proteins capable of being complex with metallic ion. These metallic
complexes are out from the cell, and these accumulate in cell membrane surface or in
the periplasmic space or are deposited in internal vacuoles called inclusion bodies.
These are called resistance mechanisms and are associated with metallothioneins and
metallohistins, molecules of intracellular storage and detoxification able to bind
heavy metals (Haferburg and Kothe 2010; Thakare et al. 2021). This may provide
an excellent source of applicable mechanisms in environment biotechnological
decontamination.
13.3.2 Precipitation
In the precipitation produced chemically stable forms of metal and only use to
reducible metals. Metabolic activity of the microorganisms contributes to the removing indirect or direct of metals, e.g. metal precipitation by secreted phosphate
generated from polyphosphate hydrolysis. In this context, the precipitation by
phosphates and sulfides has been investigated due to the low solubility of their
metal compounds. This mechanism is suggested to remove metals and actinides
from wastewater. Therefore, the selective precipitation of metals with the hydrogen
sulfide produced by sulfate-reducing bacteria (SRB) is the most studded (Joo et al.
372
M. I. Neria-González and R. Aguilar-López