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GM Microbes Invade North America
by Joe Cummins, Emeritus Professor,
University of Western Ontario
A number of GM microbes are being widely deployed since their first release six years ago. Sinorhizobium meliloti is a bacterium added to soil or inoculated into seeds to enhance nodule formation and nitrogen fixation in the roots of legumes, released in 1997.
The other commercial GM microbes are designated as biopesticides. These include GM Agrobacterium radiobacter k1026, used to prevent crown gall disease in fruit and vegetables, and Pseudomonas fluorescens modified from Bacillus thuringiensis (Bt). The modified cultures are killed by heat and provide a persistent biopesticide that degrades much more slowly in sunlight than Bt.
Neither the people selling nor those using these preparations are necessarily aware that the microbes are genetically modified. Even organic farmers may be using them inadvertently.
The commercial release of GM Sinorhizobium meliloti has resulted in GM microbes in the soil in millions of acres of cropland, where it can spread antibiotic resistance genes.
The legume symbiont, Sinorhizobium meliloti, is tremendously important for fixing nitrogen from the air into plant roots and the soil. The genetically modified commercial strain (RMBPC-2) has genes added that regulate nitrogenase enzyme (for nitrogen fixation) along with genes that increase the organic acid delivered from the plant to the nodule bacterium. It also has the antibiotic resistance marker genes for streptomycin and spectinomycin. The commercial release was permitted in spite of concerns about the impact on the environment.
Evidence supporting the initial concerns has accumulated but not dampened the use of the GM microbe. For example, a recent review reports that GM S. meliloti strains persisted in the soil for six years, even in the absence of the hosts. Horizontal gene transfer to other soil bacteria and microevolution of plasmids was observed. Other studies showed that a soil microarthropod ingested GM S. meliloti, and then a GM E. coli in the gut facilitated gene transfer to a range of bacteria.
There is little doubt that the antibiotic resistance markers for streptomycin and spectinomycin will be transferred to soil bacteria and to a range of animal pathogens. The resistance genes for streptomycin could be observed to transfer to infecting bacterium when homologous gene sequences were present.
The antibiotics spectinomycin and streptomycin are used extensively in human and animal medicine. Spectinomycin treats human gonorrhea and bovine pneumonia. Streptomycin treats human tuberculosis and Meniere’s disease and is used as a pesticide on fruits and vegetables.
The commercial release of GM Sinorhizobium meliloti has resulted in GM microbes in the soil in millions of acres of cropland, where it can spread antibiotic resistance genes.
Agrobacterium radiobacter k1026 is a biopesticide used to control the crown gall disease of fruits and trees and shrubs. Crown gall disease is caused by the bacterium Agrobacterium tumefaciens that causes tumors on plant stems, and is the most common vector employed in plant genetic engineering.
GM Agrobacterium radiobacter releases a chemical warfare agent bacteriocin (agrocin) against A. tumefaciens. Bacteriocin prevents the crown gall tumors from forming. The GM A. radiobacter has an engineered deletion in the genes so that the “male” bacterium cannot transfer its plasmid, but can act as a “female” to receive a plasmid transfer.
We may have a bioweapons equivalent of a time bomb on our hands.
However, recent research suggests that retrotransfer of genetic material can occur from “female” recipient to “male” donor bacterium.
Pseudomonas flourescens strains modified with Cry delta endotoxin genes from Bacillus thuringiensis are killed before being marketed. The killed GM bacteria are more persistent than are the conventional Bt sprays. The main fallacy in the approval of these biopesticides is to suppose that bacteria cannot enjoy sex (conjugation) after death; they do.
Soil bacteria are also easily transformed with cell lysates (squashed dead cells) and function in their genetically modified form in soil microcosms. P. fluorescens and A. tumefaciens are both transformed in soil.
…the combination of transgenic crops and GM biopesticides can create genetic combinations capable of devastating the soil microflora and microfauna.
Soil Pseudomonas and Actinobacter can also take up genes from transgenic plants. So the combination of transgenic crops and GM biopesticides can create genetic combinations capable of devastating the soil microflora and microfauna.
In conclusion, GM microbes have begun to be ubiquitous invaders of the North American ecosystem. This massive invasion took place with little or no public awareness and input, and with very little monitoring of the impact of the invasion. The environmental risk assessments of the commercial microbes were rudimentary and frequently erroneous. We may have a bioweapons equivalent of a time bomb on our hands.
Note. The full list of references for this article are posted on ISIS Members’ website http://www.i-sis.org.uk/full/GMMINAFull.php. Membership details here: http://www.i-sis.org.uk/membership.php.
[14 dec 03]