A well-functioning rhizosphere is essential for normal plant growth and health in
natural environments as well as for the efficient phytoremediation. Symbiosis
between plants and microbes can be enhanced using genetic modification tools to
make phytoremediation more efficient. For instance, the addition of a plant growth
promoting transgenic rhizobacterium Pseudomonas putida to the rhizosphere of
sunflower (Helianthus annuus), cowpea (Vigna unguiculata), wheat (Triticum
sativum), and corn (Zea spp.) was tested. The expression of a metal-binding peptide
(EC20) in the rhizosphere led to a decrease in cadmium phytotoxicity and up to 40%
increase in cadmium accumulation in the root (Wu et al. 2006).
A double genetically modified symbiotic system (both rhizobacterium and plant)
was used to improve the Cu phytostabilization in legume roots (Pérez-Palacios et al.
2017). Medicago truncatula plants expressing the metallothionein gene mt4a from
Arabidopsis thaliana in roots were used in a symbiotic system to improve the plant
Cu tolerance while the genetically modified rhizobacterium Ensifer medicae,
expressing copper resistance genes copAB from Pseudomonas fluorescens, was
used to improve the plant root Cu accumulation. Results suggested a reduced
oxidative stress and further improved root Cu accumulation without altering the
metal loading to shoots, thus leading to diminished values of the metal translocation
from roots to shoots (Pérez-Palacios et al. 2017).
24.4.2 Production of Useful Chemicals for Remediation
Technologies by GMOs (Contained Use)
Surfactant-producing microorganisms can be genetically modified to become
hyperproducing; an unpretentious yet well-cultivable strain can be advantageously
modified to become a producer. Another application may be a producer modification
to enable the use of cheap waste materials as substrates.
Currently the most promising approach is probably the in situ production in a
closed reactor, as it is acceptable by the general public. This production poses no risk
of adverse environmental effects and may enable production of such biosurfactants
that would be cost-competitive to synthetic surfactants (Sekhon et al. 2011; Rashid
et al. 2015). For example, there was a twofold increase in the biosurfactant and
esterase activities after a successful cloning of the biosurfactant genes from Bacillus
subtilis SK320 into E. coli using olive oil as a substrate. Moreover, the obtained
biosurfactant–esterase complex turned out to be a powerful emulsifier (exhibiting the
reduction of the surface tension of water from 72 dyn/cm to as low as 30.7 dyn/cm),
thus showing promise for bioremediation, hydrocarbon biodegradation, and pharmaceutical applications (Sekhon et al. 2011).
Not only can useful natural enzymes be overexpressed in hyperproduction strains
but also modified enzymes may be obtained this way, with enhanced selectivity
and/or reaction kinetics. For example, using protein engineering through combinatorial active site saturation testing (CASTing), a 5000-fold increase in k cat /K M
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M. Halecký and E. Kozliak
natural environments as well as for the efficient phytoremediation. Symbiosis
between plants and microbes can be enhanced using genetic modification tools to
make phytoremediation more efficient. For instance, the addition of a plant growth
promoting transgenic rhizobacterium Pseudomonas putida to the rhizosphere of
sunflower (Helianthus annuus), cowpea (Vigna unguiculata), wheat (Triticum
sativum), and corn (Zea spp.) was tested. The expression of a metal-binding peptide
(EC20) in the rhizosphere led to a decrease in cadmium phytotoxicity and up to 40%
increase in cadmium accumulation in the root (Wu et al. 2006).
A double genetically modified symbiotic system (both rhizobacterium and plant)
was used to improve the Cu phytostabilization in legume roots (Pérez-Palacios et al.
2017). Medicago truncatula plants expressing the metallothionein gene mt4a from
Arabidopsis thaliana in roots were used in a symbiotic system to improve the plant
Cu tolerance while the genetically modified rhizobacterium Ensifer medicae,
expressing copper resistance genes copAB from Pseudomonas fluorescens, was
used to improve the plant root Cu accumulation. Results suggested a reduced
oxidative stress and further improved root Cu accumulation without altering the
metal loading to shoots, thus leading to diminished values of the metal translocation
from roots to shoots (Pérez-Palacios et al. 2017).
24.4.2 Production of Useful Chemicals for Remediation
Technologies by GMOs (Contained Use)
Surfactant-producing microorganisms can be genetically modified to become
hyperproducing; an unpretentious yet well-cultivable strain can be advantageously
modified to become a producer. Another application may be a producer modification
to enable the use of cheap waste materials as substrates.
Currently the most promising approach is probably the in situ production in a
closed reactor, as it is acceptable by the general public. This production poses no risk
of adverse environmental effects and may enable production of such biosurfactants
that would be cost-competitive to synthetic surfactants (Sekhon et al. 2011; Rashid
et al. 2015). For example, there was a twofold increase in the biosurfactant and
esterase activities after a successful cloning of the biosurfactant genes from Bacillus
subtilis SK320 into E. coli using olive oil as a substrate. Moreover, the obtained
biosurfactant–esterase complex turned out to be a powerful emulsifier (exhibiting the
reduction of the surface tension of water from 72 dyn/cm to as low as 30.7 dyn/cm),
thus showing promise for bioremediation, hydrocarbon biodegradation, and pharmaceutical applications (Sekhon et al. 2011).
Not only can useful natural enzymes be overexpressed in hyperproduction strains
but also modified enzymes may be obtained this way, with enhanced selectivity
and/or reaction kinetics. For example, using protein engineering through combinatorial active site saturation testing (CASTing), a 5000-fold increase in k cat /K M
516
M. Halecký and E. Kozliak