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9 Phenotypic Properties of Source Microorganisms and Their Genetically Modified Derivatives
Pages 99-112

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From page 99...
... PERSISTENCE Persistence can be viewed as survival of the introduced modified microorganism or retention of particular genetic traits in new genetic combinations resulting from gene transfer. Persistence of the Microorganism If an organism cannot persist in a particular environment, it poses little threat of causing prolonged environmental impact.
From page 100...
... For example, genetically modified microorganisms introduced into the rh~zosphere for plant growth promotion or disease control will be most beneficial to farmers if the organisms remain active for years. Persistence and spread are particularly relevant, however, if a proposed application is both unfamiliar and has some potential for adverse environmental effects.
From page 101...
... The possibility that these exchanges occur, however infrequently, must be taken into consideration in any planned mtroduction. However, In the extensive trials carried out by the Monsanto Company and Clemson University in South Carolina, in which the lacZY genes were used as a marker for a genetically altered strain of Pseudomonas pnorescens, there was no evidence of exchange of the genetic marker with other soil bacteria (Drahos et al, 1988~.
From page 102...
... Unless the recipient organism has a selective advantage, the genetic transfer will have little or no consequence, there will also be no consequence if an organism has a selective advantage, but Is innocuous. Examples of genetic modifications that pose little or no risk due to genetic transfer mclude ice- (ice-nucleation deficient)
From page 103...
... It has been suggested that genetically modified microorganisms will be competitively disadvantaged, relative to their wild-type counterparts, because of burdens associated with carriage and expression of additional functions. Indeed there are many we0-documented papers to support this suggestion (Lenski and Nguyen, 1988; Brill, 1985; Davis, 1987; Zund ~d I`ebek, i980; I.ee and Edlin, 1985; Duval-~ah et al., 1981~.
From page 104...
... As introduced toxindegrading microorganisms proliferate, they and the indigenous m~croorganisms may co-exist owing to the removal of the toxic sum stance (Lenski and Hatt~ngh, 1986~. Genetic modifications also can be used to restrict substrate range, an appealing prospect for biological confinement of certain introduced microorganisms.
From page 105...
... agent will usually need to be a specialized microorganism recognizing the same host specific-signals as the pathogen and out-competing the latter. CHARACTERISTICS OF MICROBL\[ PATHOGENS One of the concerns often raised about genetic modification of rn~croorganisms is the possibility that inadvertent acquisition or loss of one or a few functions Knight convert unrelated noupathogenic organisms into potentially dangerous pathogens of humans, plants, or animals.
From page 106...
... In some cases, changes ~ virulence (increased aggressiveness on specific hosts) may be increased by acquisition of the ability to produce a toxin or by loss of an incompatibility function, but the recipient organism must already possess aD the wide variety of genes that win allow it to Infect and colonize a particular host.
From page 107...
... Also, these bacteria must be able to withstand intense solar radiation and extended periods of desiccation. Once inside the leaf, those that are pathogens now produce enzymes that degrade plant cell wads or toxins that may be very specific in terms of the cellular targets affected in certain tissues of particular hosts.
From page 108...
... Microorganisms have developed highly specialized structures (extracellular polysaccharides, fimbriae, appressoria) that provide adhesion to specific host surfaces.
From page 109...
... Pathogens can establish themselves in the host because of their ability to produce a large series of compounds, including hydrolytic and proteolytic enzymes, toxins, polysaccharides, and growth regulators that affect the host in ways that ultunately favor multiplication or transmission of the pathogen. The enzymes that destroy cell membranes or cell walls, the toxins that affect the normal metabolism of the cell, and the growth regulators that influence the ways host cells grow all have an unp act in determining pathogenesis.
From page 110...
... Although certain unique properties of pathogens are encoded by plasmas and may be transferable under certain conditions, only a limited portion of the whole array of genes required for virulence would be acquired by the recipient organism. These plasmas, therefore, can confer virulence only to related strains that are already highly adapted to particular ecological niches on or in the host.
From page 111...
... 2. Key phenotypic properties include the fitness of a genetically modified microorganism relative to its unmodified counterpart; the potential for gene transfer between the introduced rn~croorg~sm and the indigenous microflora; the physiological tolerances of the introduced microorganism; the competitiveness of the introduced microorganism; the range of substrates available to the introduced microorganism; and, if applicable, the pathogenicity, virulence, and host range of the introduced microorganism.
From page 112...
... 6. However, if the recipient is closely related to the pathogenic source, or if the recipient is itself a pathogen, increased virulence for particular hosts may result.


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