Field Testing Genetically Modified Organisms Framework for Decisions (1989) / Chapter Skim
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8 Properties of the Genetic Modification
8 Properties of the Genetic Modification
Pages 86-98
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From page 86... ...
The question has been raised whether the microorganisms produced by these methods present any risks not associated with microorganisms produced by classical microbial genetic techniques. The fact that many molecular methods provide far finer precision than has previously been available means that scientists can produce modified organisms with predictable genotypes.
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From page 87... ...
The modified genome contained no detectable foreign DNA sequences; it no longer produced the ice-nucleation protein; it did not Educe ice nucleation in vitro; and it was phenotypicaby indistinguishable from its parent in all other traits exarn~ned. It should be noted that it was selected for increased colonization, and changes in this characteristic were found.
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From page 88... ...
Molecular methods were used to delete from the plasmas the genes required for conjugal transfer (Jones et al., 1988~. The genetic alteration occurred as anticipated, and no foreign DNA sequences were detected ~ the new strain.
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From page 89... ...
GENETIC CONSIDERATIONS A number of unport ant considerations arise with respect to the actual genetic alteration of microorganisms destined for release into the environment. These considerations apply to manipulations carried out by classical microbial genetic techniques as well as to those performed with new molecular procedures.
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From page 90... ...
Alternatively, Gene cassettes can carry fragments of DNA for insertion In sites within genes of interest (Close and Rodriguez, 1982; Prentki and Kirsch, 1984~. Such insertions disrupt gene function in a manner similar to that of transposons, but they have the advantage of producing stable genetic alterations.
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From page 91... ...
The desirability of such ancillary traits must be considered within the context of the intended use of the organism. Plasrn~ds introduced into a target microorganism may be unmodified elements isolated from related or unrelated bacteria, constructs made by classical genetic means, or the products of new molecular methods.
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From page 92... ...
In Rhizobium species, it Is possible to Educe gene expression by adding secondary plant metabolites, such as flavonoids present in root exudates (Firemen et al., 1986; Peters et al., 1986; Redmond et al., 1986; Djor~jevic et al., 1987~. Similarly, certain genes in Agrobacterium strains are specifically induced by phenolic compounds, such as acetosyringone, present in plant wound exudates (Stache!
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From page 93... ...
Nevertheless, even precise genetic manipulation may produce unintended genetic changes owing to the pleiotropic nature of gene action. For example, changing a single gene may make a bacterium resistant to a bacteriophage while also changing its ability to compete for limited resources.
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From page 94... ...
Although the new genes increased the pathogenicity of the organism, in that it produced lesions on pea leaves, these genes did not convert a nonpathogen to a pathogen. Genetic Markers Marker genes, introduced for tracking or identifying the modified microorganism, can be introduced to evaluate the spread of the organism, its persistence in the intended environment, its ability to colonize a particular habitat, or its cal)
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From page 95... ...
Biological Confinement No discussion on genetic alterations would be complete without consideration of genetic manipulations intended to biologically confine the modified microorganism and its genes. Bacteria can and do exchange genetic information in the environment with low frequency (Levy and Novick, 1986; Stotzky and Babich, 1986; Tenors et al., 1987; Schofield et al., 1987~.
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From page 96... ...
One can envision that genetic modification of the doubly strandecl RNAs might lead to better control agents. If a microorganism might persist beyond the intended period of usefulness it may be necessary to utilize confinement, for example, biological confinement by suicide genes (see also Chapter 9~.
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From page 97... ...
~ other cases, the development of novel genotypes may require molecular methods. The key concern, however, Is not the method by which the microorganism is modified, but rather the phenotypic properties conferred by the microorganism's new and preexisting genomic complements.
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From page 98... ...
It also m~ be desirable to enact genetic modiRc~ions designed to Cat pers~teDce Ed minimize trouser of genetic material to the indigenous Crop.
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