12.12 Risk Mitigation in Genetically Modified Bacteria
12.12.1 Monitoring of Recombinant Strains
The monitoring of the future of environmentally released recombinant bacteria is
required which can be done by genetically selecting them through easily detectable
markers (Wilson and Lindow 1993). Earlier, lacZ, xylE and gusA genes were used in
the investigations. But, in recent times, they have been substituted with gfp genes for
green fluorescent protein (March et al. 2003) as well as lux genes of bioluminescence
(Ripp et al. 2000), which are absent in soil bacteria and can be revealed with more
sensitivity. It is very difficult to do genuine bioremediation field trials through the
use of live genetically altered bacteria due to the compliance of environmental
regulations in the United States as well as Europe. In one specific remarkable trial
which is done in large lysimeters, genetically modified P. fluorescens with the
capacity to degrade naphthalene was utilized. The existence of lux genes, a bioluminescent signal on the degradation of naphthalene and salicylate because of the
existence of lux genes, is a very unique character in designing of this bacterium
which allowed on-line observation of the degradation mechanism (Sayler and Ripp
2000).
12.12.2 Horizontal Transfer of Recombinant Genes to Other
Microorganisms
One of the most strong oppositions of this approach is that once discharged into the
environment, recombinant genes may be transferred from their host to other bacteria.
The horizontal transfer through transformation, transduction and conjugation of
several genes such as antibiotic resistance, heavy metal resistance, symbiotic as
well as degradative in different environmental conditions has been analyzed
(Davison 1999; Koch et al. 2021). It was concluded that interspecific horizontal
genes transfer for various bacteria for several genes and in different environmental
conditions. Therefore, it is quite possible that recombinant genes entered into the
environment may extend into other related bacteria if extra precautions are not taken.
Specially assessments of low, or undetectable, DNA transfer in laboratory
investigations (e.g. <10
À9 cell
À1 generation
À1 ) may not be relevant because of
large numbers of bacteria that could be discharged as well as multiplied in longer
periods. On the contrary, several techniques have been developed to decrease
horizontal gene transfer to other bacteria.
12.12.3 Use of Defective Transposons
Genetic modifications normally depend upon plasmid vectors, but they are not
appropriate for environmental discharge because of their susceptibility to horizontal
transfer (Davison 1999, 2002a, b; De Lorenzo 1994; Torres et al. 2003a). Actually,
12 Remediation of Heavy Metals Through Genetically Engineered Microorganism
349
12.12.1 Monitoring of Recombinant Strains
The monitoring of the future of environmentally released recombinant bacteria is
required which can be done by genetically selecting them through easily detectable
markers (Wilson and Lindow 1993). Earlier, lacZ, xylE and gusA genes were used in
the investigations. But, in recent times, they have been substituted with gfp genes for
green fluorescent protein (March et al. 2003) as well as lux genes of bioluminescence
(Ripp et al. 2000), which are absent in soil bacteria and can be revealed with more
sensitivity. It is very difficult to do genuine bioremediation field trials through the
use of live genetically altered bacteria due to the compliance of environmental
regulations in the United States as well as Europe. In one specific remarkable trial
which is done in large lysimeters, genetically modified P. fluorescens with the
capacity to degrade naphthalene was utilized. The existence of lux genes, a bioluminescent signal on the degradation of naphthalene and salicylate because of the
existence of lux genes, is a very unique character in designing of this bacterium
which allowed on-line observation of the degradation mechanism (Sayler and Ripp
2000).
12.12.2 Horizontal Transfer of Recombinant Genes to Other
Microorganisms
One of the most strong oppositions of this approach is that once discharged into the
environment, recombinant genes may be transferred from their host to other bacteria.
The horizontal transfer through transformation, transduction and conjugation of
several genes such as antibiotic resistance, heavy metal resistance, symbiotic as
well as degradative in different environmental conditions has been analyzed
(Davison 1999; Koch et al. 2021). It was concluded that interspecific horizontal
genes transfer for various bacteria for several genes and in different environmental
conditions. Therefore, it is quite possible that recombinant genes entered into the
environment may extend into other related bacteria if extra precautions are not taken.
Specially assessments of low, or undetectable, DNA transfer in laboratory
investigations (e.g. <10
À9 cell
À1 generation
À1 ) may not be relevant because of
large numbers of bacteria that could be discharged as well as multiplied in longer
periods. On the contrary, several techniques have been developed to decrease
horizontal gene transfer to other bacteria.
12.12.3 Use of Defective Transposons
Genetic modifications normally depend upon plasmid vectors, but they are not
appropriate for environmental discharge because of their susceptibility to horizontal
transfer (Davison 1999, 2002a, b; De Lorenzo 1994; Torres et al. 2003a). Actually,
12 Remediation of Heavy Metals Through Genetically Engineered Microorganism
349