GEMs in the polluted environment from its present restricted use in laboratory
research only (Kulshreshtha 2013).
12.10 Manipulation of Bacterial Genetic System for Enhanced
Bioremediation
In the environment, the majority of contaminants have higher persistence principally
because of suboptimal degradative pathways (Timmis and Pieper 1999). Most of the
organic contaminants are degraded through biological pathways, while harmful
inorganic metals are altered through several enzymes. Various intracellular and
extracellular events are present in bacteria which bioremediate harmful contaminants
from the environment. Under the presence of harmful metals in the environment,
tolerant bacteria produce various intracellular as well as extracellular enzymes to
eliminate or degrade the toxic type of metals to non-toxic/less toxic types. Every
enzymatic pathway possesses a step which is rate-limiting. To enhance the bioremediation capacity, manipulation of this rate-limiting step could be a solution. There are
various techniques which involve the manipulation of bacterial systems which are
given below. The current genetic engineering techniques permit the designing of
microorganisms with the ability to alter particular metal pollutants. The chances of
making artificial permutation of genes that are not found in nature give enormous
results for these GMOs which have to be used for in situ removal of metal
contaminants. The major regular techniques comprise engineering with a single
gene or operon, modification of existing gene sequences and pathway switching.
12.10.1 Engineering Single Gene or Gene Cluster/Operon
Microorganisms widespread in the high metal-contaminated sites adapt themselves
to tolerate the harmful effects through modifying several genetic processes. These
strains due to their intrinsic capability to live in a contaminated environment are
favoured for the purpose of bioremediation. Therefore, through the incorporation of
a single gene or group of genes in the intrinsic bacterium, a bacterium is produced
which because of its newly acquired adaptation of these strains is appropriate for
bioremediation purposes. Sandaa et al. (1999) observed that majority of Grampositive and α- proteobacteria are existing in heavy metal polluted soils. As most
indigenous bacteria have the capability to live in this unfavourable environment,
genetically altered recombinant strains may be utilized for increasing bioremediation. Genetic modification of local bacterial population is prefered, but the main
crisis here is that cloned genes are unstable and their transfer to the next coming
generations is also difficult. According to Lorenzo et al. (1998), minitransposons of
naturally existing Tn5 and Tn10 transposons can be utilized. These minitransposons
are unique because only the functional part of a DNA can be cut off and cloned in the
Tn5 vector to subsequently insert it into the chromosome of Gram-negative bacteria.
Ruiz et al. (2011) have done the transformation of E. coli JM109 with vectors which
12 Remediation of Heavy Metals Through Genetically Engineered Microorganism
345
research only (Kulshreshtha 2013).
12.10 Manipulation of Bacterial Genetic System for Enhanced
Bioremediation
In the environment, the majority of contaminants have higher persistence principally
because of suboptimal degradative pathways (Timmis and Pieper 1999). Most of the
organic contaminants are degraded through biological pathways, while harmful
inorganic metals are altered through several enzymes. Various intracellular and
extracellular events are present in bacteria which bioremediate harmful contaminants
from the environment. Under the presence of harmful metals in the environment,
tolerant bacteria produce various intracellular as well as extracellular enzymes to
eliminate or degrade the toxic type of metals to non-toxic/less toxic types. Every
enzymatic pathway possesses a step which is rate-limiting. To enhance the bioremediation capacity, manipulation of this rate-limiting step could be a solution. There are
various techniques which involve the manipulation of bacterial systems which are
given below. The current genetic engineering techniques permit the designing of
microorganisms with the ability to alter particular metal pollutants. The chances of
making artificial permutation of genes that are not found in nature give enormous
results for these GMOs which have to be used for in situ removal of metal
contaminants. The major regular techniques comprise engineering with a single
gene or operon, modification of existing gene sequences and pathway switching.
12.10.1 Engineering Single Gene or Gene Cluster/Operon
Microorganisms widespread in the high metal-contaminated sites adapt themselves
to tolerate the harmful effects through modifying several genetic processes. These
strains due to their intrinsic capability to live in a contaminated environment are
favoured for the purpose of bioremediation. Therefore, through the incorporation of
a single gene or group of genes in the intrinsic bacterium, a bacterium is produced
which because of its newly acquired adaptation of these strains is appropriate for
bioremediation purposes. Sandaa et al. (1999) observed that majority of Grampositive and α- proteobacteria are existing in heavy metal polluted soils. As most
indigenous bacteria have the capability to live in this unfavourable environment,
genetically altered recombinant strains may be utilized for increasing bioremediation. Genetic modification of local bacterial population is prefered, but the main
crisis here is that cloned genes are unstable and their transfer to the next coming
generations is also difficult. According to Lorenzo et al. (1998), minitransposons of
naturally existing Tn5 and Tn10 transposons can be utilized. These minitransposons
are unique because only the functional part of a DNA can be cut off and cloned in the
Tn5 vector to subsequently insert it into the chromosome of Gram-negative bacteria.
Ruiz et al. (2011) have done the transformation of E. coli JM109 with vectors which
12 Remediation of Heavy Metals Through Genetically Engineered Microorganism
345