12.9 Genetically Engineered Microorganisms
For effectively performing in situ bioremediation, collective ecological and
microbiological information as well as biochemical processes and field engineering
plan are necessary. Not only ethical issues but also several other issues obstruct a
successful production of recombinant strain. Due to biotic as well as abiotic factors,
two prominent barriers are: competition of engineered microorganism with other
natural population for nutrition and other resources and selection pressure (Singh
et al. 2011). Thus, to get the desirable results, it is necessary to opt for correct
bacterial strain in terms of growth potential as well as nutrient response. For
degrading different contaminants, several recombinant bacterial systems have been
developed. Chakrabarty and group in 1971 successfully developed the first genetically modified microbe, which was patented in 1980 in the US Supreme Court. It
was modified from the genus Pseudomonas, which have the ability to degrade crude
oil constituents (Ezezika and Singer 2010; Kumar et al. 2013).
These GEMs are produced through the detection and modifications of some
specific genetic sequences. GEMs show increased degradability for a broad variety
of xenobiotics from various environmental sources and have the capability to
bioremediate them. GEM designing is dependent on the knowledge of microbes
and xenobiotic interaction and its genetic base, biochemical processes, the structure
of operon, molecular biology and its ecological application.
Various strategies are available for the production of GEMs for bioremediation.
In the first strategy, organisms appropriate for modification with the relevant genes
are recognized. For example, microorganisms suitable to thrive in soil environment
cannot adapt to the aquatic environment and therefore cannot be employed effectively. Thus, aquatic microbes can be employed for producing GEMs to
bioremediate aquatic sources. The supplementation of nutrients to the inoculated
environment is not required in the application of these organisms which decrease the
costs as well as maintenance. Anabaena sp. and Nostoc ellipsosporum are generated
through inserting linA of P. paucimobilus and fcbABC of Arthrobacter globiformis,
respectively. The gene linA regulates the biodegradation of lindane (γ-hexachlorocyclohexane), while fcbABC provides the capacity to biodegrade
halobenzoates, which can be employed to remediate these contaminants of water
sources.
In the second strategy, pathway construction, extension and regulation is done.
GEMs are produced through improvement in already present catabolic pathways or
extension of these pathways for degrading those compounds which wild strains
cannot degrade. The entire catabolic pathway is coded either by a single microorganism or through a group of microorganisms executing single or many stages in the
bioremediation of xenobiotics. In this manner, manufactured GEMs have degradation capacities of diverse microbial communities because of modification in gene
sequences which ultimately improve the effectiveness and value of the catabolic
pathways.
Enzyme specificity and affinity are modified in the third strategy. Transcription
and translation of specific genes produce enzymes which catalyze different steps of
12 Remediation of Heavy Metals Through Genetically Engineered Microorganism
343
For effectively performing in situ bioremediation, collective ecological and
microbiological information as well as biochemical processes and field engineering
plan are necessary. Not only ethical issues but also several other issues obstruct a
successful production of recombinant strain. Due to biotic as well as abiotic factors,
two prominent barriers are: competition of engineered microorganism with other
natural population for nutrition and other resources and selection pressure (Singh
et al. 2011). Thus, to get the desirable results, it is necessary to opt for correct
bacterial strain in terms of growth potential as well as nutrient response. For
degrading different contaminants, several recombinant bacterial systems have been
developed. Chakrabarty and group in 1971 successfully developed the first genetically modified microbe, which was patented in 1980 in the US Supreme Court. It
was modified from the genus Pseudomonas, which have the ability to degrade crude
oil constituents (Ezezika and Singer 2010; Kumar et al. 2013).
These GEMs are produced through the detection and modifications of some
specific genetic sequences. GEMs show increased degradability for a broad variety
of xenobiotics from various environmental sources and have the capability to
bioremediate them. GEM designing is dependent on the knowledge of microbes
and xenobiotic interaction and its genetic base, biochemical processes, the structure
of operon, molecular biology and its ecological application.
Various strategies are available for the production of GEMs for bioremediation.
In the first strategy, organisms appropriate for modification with the relevant genes
are recognized. For example, microorganisms suitable to thrive in soil environment
cannot adapt to the aquatic environment and therefore cannot be employed effectively. Thus, aquatic microbes can be employed for producing GEMs to
bioremediate aquatic sources. The supplementation of nutrients to the inoculated
environment is not required in the application of these organisms which decrease the
costs as well as maintenance. Anabaena sp. and Nostoc ellipsosporum are generated
through inserting linA of P. paucimobilus and fcbABC of Arthrobacter globiformis,
respectively. The gene linA regulates the biodegradation of lindane (γ-hexachlorocyclohexane), while fcbABC provides the capacity to biodegrade
halobenzoates, which can be employed to remediate these contaminants of water
sources.
In the second strategy, pathway construction, extension and regulation is done.
GEMs are produced through improvement in already present catabolic pathways or
extension of these pathways for degrading those compounds which wild strains
cannot degrade. The entire catabolic pathway is coded either by a single microorganism or through a group of microorganisms executing single or many stages in the
bioremediation of xenobiotics. In this manner, manufactured GEMs have degradation capacities of diverse microbial communities because of modification in gene
sequences which ultimately improve the effectiveness and value of the catabolic
pathways.
Enzyme specificity and affinity are modified in the third strategy. Transcription
and translation of specific genes produce enzymes which catalyze different steps of
12 Remediation of Heavy Metals Through Genetically Engineered Microorganism
343