by Prof. Joe Cummins
While the attention
of the world is focused on genetically modified (GM)
crops, GM microbes have been released for at least six
years with little or no public awareness or debate.
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. It was released for commercial production in 1997.
The other commercial GM microbes are designated as bio-pesticides.
These include GM,
Agrobacterium radiobacter k1026, used to prevent
crown gall disease in fruit and vegetable plants
Pseudomonas fluorescens modified with a number of different Cry delta-endotoxin
genes from different subspecies of Bacillus thruingiensis (Bt)
The modified P. fluorescens cultures are
killed by heat pasteurization and provides a persistent biopesticide
preparation that degrades much slower in sunlight than Bt.
Neither the people selling nor those using the preparations are
necessarily aware that the microbes are genetically modified,
however. Even organic farmers may be using them inadvertently.
The legume symbiont, Sinorhizobium meliloti, is tremendously
important for fixing nitrogen from the air into plant roots and the
soil. Legumes signal to the bacterium by exuding flavonoids from
their roots, activating the expression of nodulation genes in the
bacterium, resulting in the production of Nod factors that regulate
the formation of nitrogen fixing root nodules .
The S. meliloti genome has been fully
sequenced. It is unusual in containing three chromosomes (or a
chromosome and two very large plasmids), all of them contributing to
the symbiosis with the plant roots .
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 of the GM microbe on the environment.
Evidence supporting the initial concerns has accumulated but that
has 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 legume hosts. Horizontal gene
transfer to other soil bacteria and microevolution of plasmids was
Other studies showed that a soil micro
arthropod ingested GM S. meliloti, and a GM E. coli in the arthropod
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. For example, the resistance
genes for streptomycin could be observed to transfer from their
insertion as transgenes in plant chloroplast to infecting bacterium
Actinobacter sp.  when homologous gene sequences were
The antibiotics spectinomycin and streptomycin are used extensively
in human and animal medicine. Spectinomycin is used to treat human
gonorrhea  and bovine pneumonia .
Streptomycin is used to treat human
tuberculosis  and Meniere’s disease 
and as a pesticide on fruits and vegetables . Thus,
the commercial release of GM Sinorhizobium meliloti has resulted in
the establishment of the GM microbe in the soil in millions of acres
of cropland, where it can spread antibiotic resistance genes for
antibiotics that are extensively in use in medicine and agriculture.
Agrobacterium radiobacter k1026  is a bio-pesticide
derived from A. radiobacter k84, a natural bacterium used to control
the crown gall disease of fruits and ornamental trees and shrubs.
Crown gall disease is due to the bacterium Agrobacterium tumefaciens
that causes tumors to form on the 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 is a novel
nucleic acid derivative that prevents the crown gall tumors from
forming in the infected plants. The GM A. radiobacter has an
engineered deletion in the genes controlling plasmid transfer so
that the ‘male’ bacterium cannot transfer its plasmid, but it can
act as a ‘female’ to receive a plasmid transfer.
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 B. thuringiensis 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.
tumefacians are both transformed in soil .
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
GM microbes have begun to be ubiquitous invaders of
the North America 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
We may have a bio-weapons equivalent of
a time bomb on our hands.
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Regulation of root nodule development Ann. Rev Genet 1998,
Galibert F. et al (55 authors).
The composite genome of the legume symbiont Sinorhizobium
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INFORMATION SYSTEMS FOR
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EPA fact sheet "Agrobacterium radiobacter k1026 1999
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