The Way Ahead - Environmental Biotechnology: Theory and Application - page 275

polyhedrin protein would be expected to lessen NPV survival in the wild and
certainly reduce their infectivity thus making them poor vectors for the spread
of 'foreign' genes.
Another area of major concern is that that many of the constructs released into
the environment carry genes for antibiotic resistance. In Chapter 9, the rationale
for including such genes was described but, briefly, its function is during the con-
struction of the recombinant and, especially in eukaryotic recombinants, serves
no function in the final GMO. This being the case, it can be argued that it is
reasonable to require the removal of all such selector and reporter genes before
release of the GMO. Accordingly, it is especially true because of the limited
number of selector and reporter genes in current use. Consequently, it is likely
that while the gene or genes of interest may be unique, or almost so, to that
construct, it will probably be carrying one of a very limited number of selector
or reporter genes. As a result, the total number of GMOs released worldwide in
one year, carrying one particular selector or reporter gene could be very high
indeed. Given that true figures for the rate of gene transfer between unrelated
organisms (horizontal transfer) have not yet been satisfactorily estimated, it would
seem prudent to err on the side of caution and remove all unnecessary genetic
material, prior to GMO release.
Attempts to estimate the rate of gene transfer in the environment are being
made using microcosms. These are small-scale reproductions of an enclosed test
environment. One such experiment investigated the effect of simulated light-
ning on the rate of plasmid transfer between bacteria. Their results showed an
increase in transformation suggesting that, under certain conditions, lightning is
able to make bacterial cells competent to receive plasmid DNA by horizontal
transfer (Demaneche 2001). Microcosms are useful test systems especially as
in this example, where the question being asked is very specific, but they have
their limitations in the assessment of wider horizontal gene transfer, due to the
difficulties in recreating the natural environment. It seems likely that many ques-
tions regarding the spread of genes will not be answered until sufficient GMOs
have been released and the ensuing results monitored. It is clear that much more
research is required into the balance between real benefits and risks of genetically
engineered plants (Wolfenbarger and Phifer 2000).
Closing Remarks
In the final analysis, life is enormously robust and resilient, not perhaps at an
individual level, but certainly on a gross scale. Living things, and most especially
microbes, have colonised a truly extensive range of habitats across the planet,
and some of these are, as has been discussed, extremely challenging places. This,
combined with the lengthy history of bacteria and archaea, which has equipped
many species with an amazing array of residual metabolic tools, adds up to a
remarkable reservoir of capabilities which may be of use to the environmental