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5. Bioconfinement of Viruses, Bacteria, and Other Microbes
Pages 159-179

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From page 159...
... Modern molecular methods allow us to broaden the range of useful applications, and all of the evidence indicates that the methods used to generate genetically engineered organisms (GEOs) are not intrinsically dangerous.
From page 160...
... The committee suggests that genetically engineered microbes be reconsidered on their own. POTENTIAL EFFECTS OR CONCERNS, AND NEED FOR BIOCONFINEMENT IN VIRUSES, FUNGI, AND BACTERIA The three potential areas of concern that attend the release of genetically engineered bacteria, fungi, and viruses are similar to those for any other class of GEO: invasion, displacement, and transfer.
From page 161...
... . The latter adaptation exemplifies the potential consequence of releasing genetically engineered viruses into an ecological community of naÔve (inexperienced)
From page 162...
... The common practice is to apply nutrients, such as nitrate and phosphate, to the contaminated area to promote growth of indigenous bacterial populations, which likely will include microbes that can metabolize the pollutants. As a rule, introducing genes into indigenous bacteria to perform a specific function is preferable to introducing exotic bacteria that contain
From page 163...
... Also, cases have been reported in which genetically engineered bacteria coexist with indigenous populations (Kargatova et al., 2001)
From page 164...
... Displacement of Indigenous Populations Viruses It is theoretically possible that genetically engineered viruses could displace resident species. In theory, the coevolutionary battle between viruses and their hosts leads to a never-ending arms race; hosts evolve resistance, viruses evolve counterresistance, and the cycle repeats with both species constantly running to remain in place (this is the "Red Queen hypothesis"; Clarke et al., 1994)
From page 165...
... The limited available data suggest that the introduction of genetically engineered microbes into the environment is unlikely to have significant long-lasting effects on microbial communities. Horizontal Genetic Transfer into Local Populations A third concern of introducing genetically engineered microbes is the potential consequence of horizontal transfer of engineered genes from introduced microbes into local populations.
From page 166...
... to create the potential for engineered alleles to enter and circulate within a local gene pool. Laboratory experiments show that gene exchange can profoundly affect virus evolution (Rambaut et al., 2004; Turner, 2003; Turner and Chao, 1998)
From page 167...
... . Thus, plants have ready access to the gene pool of Gram-negative bacteria, thereby expanding the possibilities of horizontal gene transfer from prokaryotes to eukaryotes.
From page 168...
... If any antibiotic resistance loci are used to mark strains, the resistance loci should not involve antibiotics that currently are in clinical use. A sensible choice should be made for the bacterial strain introduced into the environment to carry out a specific function.
From page 169...
... Fitness Reduction Phenotypic Handicapping One potential consequence of releasing transgenic microbes to the environment is that they could perpetuate by invading or displacing natural populations in competition for resources. The limited experimental data suggest that, in general, genetically engineered bacteria and viruses will be competitively less fit than their wild-type counterparts because of burdens associated with carrying and expressing additional functions coded by transgenes.
From page 170...
... Phenotypic handicapping of bacteria as a confinement measure already has been alluded to: One form involves the rapid decline of nonindigenous microbial strains (including genetically altered ones) after they are introduced into soil or aquatic environments (e.g., Glandorf et al., 2001; Scanferlato et al., 1989)
From page 171...
... Rather, in their natural environment, bacteria often form highly structured clumps, called biofilms, with properties that are quite different from those of bacteria growing in the laboratory. For this reason, phenotypic handicapping of transgenic bacteria growing in liquid medium in the laboratory might not be relevant to performance in a natural setting.
From page 172...
... Another proposed technique is to render the fungi asporogenic (unable to produce spores) , thereby helping not only to prevent their spread but also inhibiting the formation of dormant resting structures that resist heat, cold, desiccation, and other harsh environmental conditions (Gressel, 2001)
From page 173...
... Thus, if the fungus is to be used in biocontrol, an asporogenic mutant would not be suitable, and this form of handicapping would be inappropriate. Suicide Genes Suicide genes can be used to confine bacteria and fungi under two circumstances.
From page 174...
... Molin and colleagues (1993) reviewed the major systems of suicide genes developed in bacteria.
From page 175...
... Such targets could involve reproduction, spore formation, and spore germination. To prevent vegetative spread of the mycelium, suicide genes could be engineered into cells under the control of an inducible promoter.
From page 176...
... Thus, unlike most eukaryotes, they are not bound to obligate sexual reproduction. As a consequence, confinement of genetically engineered microbes must be limited to fitness reduction methods such as the induction of suicide genes or phenotypic handicapping.
From page 177...
... . Phenotypic handicapping and other fitness reduction methods are designed to reduce local survival of introduced bacteria, fungi, and viruses.
From page 178...
... . The committee believes that the ecological consequences of using fitness reduction methods, such as phenotypic handicapping and suicide systems in genetically engineered microbes, are likely to be minimal, because those methods are designed to employ genotypes that are competitively inferior indigenous strains.
From page 179...
... However, most transgenic microalgae have been cultivated in closed-system indoor tanks and are not intended for release into natural environments. Because of their similarity to bacteria, phenotypic handicapping and suicide systems should provide effective bioconfinement if necessary.


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