Dale and others: GE-Bt is not the same as conventional soil microbe Bt. The
key differences include:
a) GE-Bt is formed in each plant pesticidal cell as an active endotoxin. It
exists in that form in each cell through its lifespan and enters the soil in
that form when the plant dies. Soil microbe Bt exists in each microbe as an
*inactive* precurser which becomes activated only under very specialized
circumstances in the gut of particular organisms.
b) original Bt is rapidly broken down by UV etc. when applied as a foliar
spray. GE-Bt, once it is in the soil, retains insecticidal activity for at
least 6 months, according to a series of articles from the lab of Stotzky at NY
University (e.g. Tapp, H. and G. Stotzky. 1998. Persistence of the insecticidal
toxin from Bt subsp. Kurstaki in soil. Soil Biol. Biochem. 30:471-476). It is
true that GE-Bt is a substrate for microbial degradation and does decay in the
soil, but consider the issue of scale (see below).
c) It was this lab that showed in a recent article (Saxena, D., S. Flores, and
G. Stotzky. 1999. Insecticidal toxin in root exudates from Bt corn. Nature
402:480) another key difference between original and GE Bt. GE Bt plants
actively exude active endotoxin during their lifetime, so the insecticidal
properties of GE Bt need not wait until plant death to exert their effects, if
any, on soil biota.
d) Other studies showing an effect of other transgenic plants (not Bt) on soil
biota include the following:
Donegan, K.K., R.J. Seidler, V.J. Fieland, D.L. Schaller, C.J. Palm, L.M. Ganio,
D.M. Cardwell, and Y. Steinberger. 1997. Decomposition of genetically engineered
tobacco under field conditions: persistence of proteinase inhibitor I product
and effects on soil microbial respiration and protozoa, nematode and
microarthropod populations. J. Applied Ecology 34:767-777.
Doyle, J.D., G. Stotzky, G. McClung, and C.W. Hendricks. 1995. Effects of
genetically engineered microorganisms on microbial populations and processes in
natural habitats. Adv. Appl. Micro. 40.
Giovanni, G.D., L.S. Watrud, R.J. Seidler, and F. Widmer. 1999. Comparison of
parental and transgenic alfalfa rhizosphere bacterial communities using biolog
GN metabolic fingerprinting and Enterobacterial Repetitive Intergenic Consensus
Sequence -PRC (ERIC-PCR). Microb. Ecol. 37:129-139.
e) Not only does GE Bt expose humans, fed livestock, soil biota, and everything
else to a completely unprecedented endotoxin (e.g. active, not the precursor),
but it also does so on an inconceivably larger scale - every cell of every plant
on tens of millions of hectares every year.
No, this is not the same as soil microbe Bt, not by a long shot. Ann
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