Root nodule bacteria with Bt transgene tended to displace
non-manipulated bacteria in legume root nodules.
Manipulated Organism:
The root nodule bacterium Rhizobium leguminosarum, which colonizes
the roots of legumes and helps the plants fix nitrogen.
Inserted Transgenes:
cryIIIAb for the production of delta-endotoxin, derived from
Bacillus thuringiensis (Bt). The gene was fused to a promoter
that "responds to legume root exudates and gives enhanced levels of toxin
expression in the rhizosphere" (Giddings et al. 1997, p. 1063).
Goal:
Give legumes, via the root nodule bacterium, the capacity to produce
delta-endotoxin. delta-endotoxin is an insecticide and is intended in this
case to kill the larvae of the insect Sitona, which feed on legume
roots and their root nodules.
Target Effect:
Some of the transgenic bacteria strains gave the plants a degree of
protection from the pest (Skøt et al. 1994).
Nontarget Effects:
The researchers found (Giddings et al. 2000) that when a mixed culture
(1:1) of unmanipulated and transgenic nodule bacteria
is introduced into the soil to inoculate pea plants, there is not,
subsequently, a 1:1 distribution of nodule occupation by the two types of
bacteria. Rather, the transgenic bacteria "outcompete" the unmanipulated
controls and occupy two-thirds of the nodules. In lab cultures, the growth
rates of unmanipulated bacteria and transgenic bacteria were the same.
Additional Comments:
The authors summarize: "These results demonstrate that the ecological
and agronomic characters of transgenics might be unexpectedly altered
by transformation. Such characters might have a bearing on the safety
and/or success of transgenics released into the environment" (Giddings
et al. 2000).
Source:
Giddings, G., L. Mytton, L. Taylor, S. Thomas et al. (2000). "A Secondary
Effect of Transformation in Rhizobium leguminosarum for Bacillus
thuringiensis subspecies tenebrionis delta-endotoxin
(cryIIIA) Genes. Part 2," Theor Appl Genet vol. 100, pp. 820-3.
Giddings, G., L. Mytton, M. Griffiths, A. McCarthy et al. (1997). "A
Secondary Effect of Transformation in Rhizobium leguminosarum
for Bacillus thuringiensis subspecies tenebrionis
delta-endotoxin (cryIIIA) Genes. Part 2," Theor Appl Genet
vol. 97, pp. 1062-8.
Skøt, L., E. Timms, L. Mytton (1994). "The Effect of Toxin-Producing
Rhizobium Strains on Larvae of Sitona flavescens Feeding
on Legume Roots and Nodules," Plant Soil vol. 163, pp. 141-50.
Author Affiliations:
Institute of Biological Sciences, University of Wales, UK.
Funding:
Not reported.
Product Status:
Not on the market as of 2008.
Copyright 2008 The Nature
Institute.
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