Biomedical Engineering Reference
In-Depth Information
Early trials of this technique, if it is developed, will likely rely on the basic science research
that has characterized much of the biology in the well developed bioaugmentation systems.
A hypothetical case study, discussing the steps to successfully introducing a vinyl chloride
reductase gene (
vcrA
) into a contaminated environment using this technique, is described below.
12.5.4.1 Viral Bioaugmentation of
: A Thought Experiment
The reductive dehalogenase
vcrA
is one of the few biochemically characterized reductive
dehalogenases (RDases). It is active in the crucial dechlorination step of VC to ethene (Muller
et al.,
2004
), and is thus of significant interest for both bioaugmentation of sites containing
chlorinated ethenes and as a marker gene for determining a site's native dechlorination potential.
With
vcrA
's known substrate specificity, it might be possible to target VC dechlorination by
transferring this RDase to natively occurring
Dehalococcoides
or other dechlorinating organ-
isms. This transfer could potentially be accomplished by introducing the
vcrA
gene on a virus,
bacteriophage or mobile element into the environment in high copy numbers. Subsequent phage
infection or other mode of DNA intake could lead to integration of the
vcrA
gene into a native
dechlorinating organism. Ultimately this could lead to an introduction of VC reductase capability
at a site that was previously stalled at the VC to ethene dechlorination step.
Interestingly, the
vcrA
gene in
Dhc
strain VS has a codon bias indicative of a recent
acquisition of this gene within the genome (McMurdie et al.,
2007
). A similar unusual codon
bias is present in the VC reductase
bvcA
within
Dhc
strain BAV1 (Krajmalnik-Brown et al.,
2004
; McMurdie et al.,
2007
). Both of these key genes are present in high plasticity regions of
the
Dhc
genome structure, where the majority of genetic integration events have taken place,
and are hypothesized to be present on “genomic islands” - large mobile elements within the
genomes (McMurdie et al.,
2009
).
The evidence for
vcrA
and
bvcA
being recent acquisitions within
Dhc
genomes supports the
potential for their use as independent bioaugmentation tools, as there is clear evidence that
Dhc
strains are capable of integrating and subsequently transcribing a novel reductive dehalogenase
gene, leading to an increased substrate range. There has been little to no research on the
mechanisms of DNA uptake and gene transfer in
Dehalococcoides
, and so it is unclear whether
this strategy could be effective on an industrial scale. However, if a system of
vcrA
delivery,
genomic incorporation and enzyme translation could be developed, it would be a powerful new
tool for bioaugmenting sites that exhibit partial dechlorination profiles.
vcrA
Future Perspectives
Advances in bioremediation and bioaugmentation will come both from:
Discovery of new organisms with new degradative capabilities.
Development of entirely novel approaches, likely combining biotic and abiotic technologies.
Biosensors are potentially a powerful tool for monitoring site remediation.
Designer microbes and directed lateral gene transfer are useful genetic modification techniques for
developing targeted, site-specific bioremediation strategies.
Viruses could be used to inoculate a specific site with specific gene or function, without the need for
bacterial cultures.
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