Insights into the Status of Heavy Metal Resistant Rhizobacterial …
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Biosorption of heavy metals from the contaminated site by means of microbes are
associated within the cell wall and functional groups like –SH, –OH, and –COOH and
other biomolecules have more affinity for heavy metals. Metal-binding peptides and
chelators involved in metal binding such as metallothioneins (MT) and glutathione—
derived peptides (PC). These PC and MT are secreted by rhizosphere fungi, bacteria
and also by plants in response to heavy metals stress (Miransari 2011).
4.3 Mechanisms Behind the Utility of Heavy Metals
by Microorganisms
Heavy metal ions are trapped by the cellular structure of microorganisms and consequently attached to the binding sites of the cell wall (Malik 2004). This method
is known as passive uptake or biosorption, and is exclusively independent of the
metabolic cycles. The amount of metals biosorbed depends on the kinetic equilibrium
and composition of the metals at the cellular surface. The mechanism involves several
process including electrostatic interaction, ion exchange and surface complexation.
Absorption of heavy metal is carried out by fragments of cells and tissues, or living
cells or by dead biomass as passive uptake by surface complexation on the cell
wall and other outer layers (Fomina et al. 2014). In cellular metabolic cycles, these
heavy metal ions may pass across the cell membrane and the process is known as
bioaccumulation or active uptake.
4.4 Bioaccumulation or Active Uptake of Heavy Metals
in Bacteria
In gram positive bacteria peptidoglycan layer contains alanine, glutamic acid, mesodiaminopimelic acid, polymers of glycerol and teichoic acid whereas in gram negative bacteria, cell wall contains enzymes, lipoproteins, glycoproteins, lipopolysaccharides and phospholipids which concerned as the active site for metal binding
(Lesmana et al. 2009; Fomina et al. 2014; Gupta et al. 2015). The process involved
in the bioaccumulation of heavy metals in the living cell is dependent on a variety
of physical, chemical and biological mechanisms. The intercellular and extracellular
process plays a partial and ill-defined role in biosorption as well (Fomina et al. 2014).
The microbes which accumulate heavy metals have the tolerance capacity to one or
more metals at higher concentrations, and it has the ability to change the toxic forms
to harmless forms thereby reducing the toxic levels of the metals in the environment
(Fig. 1). Simultaneously these organisms do retain the heavy metals contained in the
cells (Mosa et al. 2016).
Microorganisms hide many kinds of metal-binding metabolites and produce extracellular polymeric substances like polysaccharides and associated components such
25
Biosorption of heavy metals from the contaminated site by means of microbes are
associated within the cell wall and functional groups like –SH, –OH, and –COOH and
other biomolecules have more affinity for heavy metals. Metal-binding peptides and
chelators involved in metal binding such as metallothioneins (MT) and glutathione—
derived peptides (PC). These PC and MT are secreted by rhizosphere fungi, bacteria
and also by plants in response to heavy metals stress (Miransari 2011).
4.3 Mechanisms Behind the Utility of Heavy Metals
by Microorganisms
Heavy metal ions are trapped by the cellular structure of microorganisms and consequently attached to the binding sites of the cell wall (Malik 2004). This method
is known as passive uptake or biosorption, and is exclusively independent of the
metabolic cycles. The amount of metals biosorbed depends on the kinetic equilibrium
and composition of the metals at the cellular surface. The mechanism involves several
process including electrostatic interaction, ion exchange and surface complexation.
Absorption of heavy metal is carried out by fragments of cells and tissues, or living
cells or by dead biomass as passive uptake by surface complexation on the cell
wall and other outer layers (Fomina et al. 2014). In cellular metabolic cycles, these
heavy metal ions may pass across the cell membrane and the process is known as
bioaccumulation or active uptake.
4.4 Bioaccumulation or Active Uptake of Heavy Metals
in Bacteria
In gram positive bacteria peptidoglycan layer contains alanine, glutamic acid, mesodiaminopimelic acid, polymers of glycerol and teichoic acid whereas in gram negative bacteria, cell wall contains enzymes, lipoproteins, glycoproteins, lipopolysaccharides and phospholipids which concerned as the active site for metal binding
(Lesmana et al. 2009; Fomina et al. 2014; Gupta et al. 2015). The process involved
in the bioaccumulation of heavy metals in the living cell is dependent on a variety
of physical, chemical and biological mechanisms. The intercellular and extracellular
process plays a partial and ill-defined role in biosorption as well (Fomina et al. 2014).
The microbes which accumulate heavy metals have the tolerance capacity to one or
more metals at higher concentrations, and it has the ability to change the toxic forms
to harmless forms thereby reducing the toxic levels of the metals in the environment
(Fig. 1). Simultaneously these organisms do retain the heavy metals contained in the
cells (Mosa et al. 2016).
Microorganisms hide many kinds of metal-binding metabolites and produce extracellular polymeric substances like polysaccharides and associated components such