raises the effectiveness of bioremediation. Biochar is presently being used for its
capability of managing heavy metal polluted soils (Namgay et al. 2010). When the
contaminated soil was remediated with biochar, less availability of heavy metals is
observed which decreased plant absorption of the metals. Biochar has the capability
to increase soil pH unlike other organic amendments because properties of biochar
differ generally on the basis of its production process and on the feedstock employed
in its making. The influence of various biochar amendments depends on the accessibility of heavy metals occurring in soil. Additional research is required for understanding the influence of biochar on soil microorganisms as well as effects of the
interaction between biochar and soil microbes on remediation of heavy metal
polluted soils as these studies are very few (Singh et al. 2015).
12.5 Unique Mechanisms in Bacteria: Natural Development
of Resistance Towards Toxic Elements
Bacteria are known to flourish in every type of environment, covering from frigid
poles to the hot deserts, to the wet swamps, to the aquatic systems. They have some
special properties like tiny in size, having large surface-area-to-volume ratio, capable
to move genetic characters and their flexibility. Bacteria generally degrade organic
pollutants into non-hazardous products by using them as a carbon source. But, for
inorganic metal contamination, microorganisms employ three different tolerance
mechanism, like flushing of the contaminant metals out of the cell through
transporters, conversion of the metals into harmless forms and biosorption. Mostly,
biosorption and the enzymatic change of metal into another form are joined, meaning
once a metal is absorbed inside the cell, enzymes will precipitate it in the form of salt
(Williams et al. 2012). The primary line of defence against heavy metals is efflux,
which includes heavy metal efflux resistance nodulation cell division (HME-RND)
protein superfamily members together with efflux pumps (Nies 2003). The second
process through which bacteria are known to tolerate as well as get rid of harmful
metals is biosorption (Vieira and Volesky 2010), which is actually the binding of
contaminants at the surface of the cell. It includes the biosorbent, a biological
material which is a solid phase and solvent (liquid phase) with the dissolved species
which has to be absorbed (sorbate, metal ions). The affinity of sorbent to sorbate is
retained until equilibrium is reached between the sum of solid-bound sorbate species
and its residual part in the solution, till the sorbate is removed. In bacteria,
metallothioneins (MTs), a group of proteins that are cysteine rich having a molecular
weight of 0.5–14 kDa, mediate sorption of metals (Blindauer et al. 2002). In certain
cases, they may also contain histidine residues. It is already known that microbial
metallothioneins behave like a storehouse for zinc also guard the cells from cadmium
toxicity (Klaassen and Liu 1999). They may also work as free radical scavengers and
bind with toxic superoxide and hydroxide ions. Cysteine is changed into cystine by
oxidation and release bound metals in the environment. The biosorption mechanism
regenerates biosorbent perfectly and has very efficient possibilities of metal recovery
(Kratchovil and Volesky 1998). But, sometimes, early saturation of metal-interactive
12 Remediation of Heavy Metals Through Genetically Engineered Microorganism
321
capability of managing heavy metal polluted soils (Namgay et al. 2010). When the
contaminated soil was remediated with biochar, less availability of heavy metals is
observed which decreased plant absorption of the metals. Biochar has the capability
to increase soil pH unlike other organic amendments because properties of biochar
differ generally on the basis of its production process and on the feedstock employed
in its making. The influence of various biochar amendments depends on the accessibility of heavy metals occurring in soil. Additional research is required for understanding the influence of biochar on soil microorganisms as well as effects of the
interaction between biochar and soil microbes on remediation of heavy metal
polluted soils as these studies are very few (Singh et al. 2015).
12.5 Unique Mechanisms in Bacteria: Natural Development
of Resistance Towards Toxic Elements
Bacteria are known to flourish in every type of environment, covering from frigid
poles to the hot deserts, to the wet swamps, to the aquatic systems. They have some
special properties like tiny in size, having large surface-area-to-volume ratio, capable
to move genetic characters and their flexibility. Bacteria generally degrade organic
pollutants into non-hazardous products by using them as a carbon source. But, for
inorganic metal contamination, microorganisms employ three different tolerance
mechanism, like flushing of the contaminant metals out of the cell through
transporters, conversion of the metals into harmless forms and biosorption. Mostly,
biosorption and the enzymatic change of metal into another form are joined, meaning
once a metal is absorbed inside the cell, enzymes will precipitate it in the form of salt
(Williams et al. 2012). The primary line of defence against heavy metals is efflux,
which includes heavy metal efflux resistance nodulation cell division (HME-RND)
protein superfamily members together with efflux pumps (Nies 2003). The second
process through which bacteria are known to tolerate as well as get rid of harmful
metals is biosorption (Vieira and Volesky 2010), which is actually the binding of
contaminants at the surface of the cell. It includes the biosorbent, a biological
material which is a solid phase and solvent (liquid phase) with the dissolved species
which has to be absorbed (sorbate, metal ions). The affinity of sorbent to sorbate is
retained until equilibrium is reached between the sum of solid-bound sorbate species
and its residual part in the solution, till the sorbate is removed. In bacteria,
metallothioneins (MTs), a group of proteins that are cysteine rich having a molecular
weight of 0.5–14 kDa, mediate sorption of metals (Blindauer et al. 2002). In certain
cases, they may also contain histidine residues. It is already known that microbial
metallothioneins behave like a storehouse for zinc also guard the cells from cadmium
toxicity (Klaassen and Liu 1999). They may also work as free radical scavengers and
bind with toxic superoxide and hydroxide ions. Cysteine is changed into cystine by
oxidation and release bound metals in the environment. The biosorption mechanism
regenerates biosorbent perfectly and has very efficient possibilities of metal recovery
(Kratchovil and Volesky 1998). But, sometimes, early saturation of metal-interactive
12 Remediation of Heavy Metals Through Genetically Engineered Microorganism
321