By Barbara H. Peterson
There is long list of dangers inherent in genetically modifying our food supply, which includes:
- Cross-species viruses
- New bacteria
- Antibiotic resistance
- Reactivation of dormant viruses
- New, never before seen genes
- Destruction of the environment
The question is, can we add e-coli contamination to this list?
Escherichia coli (commonly abbreviated E. coli; named after Theodor Escherich) is a Gram negative rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms (endotherms). Most E. coli strains are harmless, but some, such as serotype O157:H7, can cause serious food poisoning in humans, and are occasionally responsible for product recalls. The harmless strains are part of the normal flora of the gut, and can benefit their hosts by producing vitamin K2, and by preventing the establishment of pathogenic bacteria within the intestine.
E-coli live in the gut, and are beneficial. That is, unless we ingest one that has mutated into a harmful strain, and then it can cause disease.
Given the natural tendency of this bacteria to mutate, could we be facing the widespread contamination of our food supply with genetically modified plants containing a mutated form of disease-causing e-coli?
It is a mistake to think of E. coli as a homogeneous species. Most genes, even those encoding conserved metabolic functions, are polymorphic, with multiple alleles found among different isolates . The composition of the genome of E. coli is also highly dynamic. The fully sequenced genome of the laboratory K-12 strain [used by Lederberg in 1948] , whose derivatives have served an indispensable role in the laboratories of countless scientists, shows evidence of tremendous plasticity . It has been estimated that the K-12 lineage has experienced more than 200 lateral (horizontal) transfer events since it diverged from Salmonella about 100 million years ago and that 18% of its contemporary genes were obtained horizontally from other species . Such fluid gain and loss of genetic material are also seen in the recent comparison of the genomic sequence of a pathogenic E. coli O157:H7 with the K-12 genome. Approximately 4.1 million base pairs of ‘backbone’ sequences are conserved between the genomes, but these stretches are punctuated by hundreds of sequences present in one strain but not in the other. The pathogenic strain contains 1.34 million base pairs of lineage-specific DNA that includes 1,387 new genes; some of these have been implicated in virulence, but many have no known function .
The virulence factors that distinguish the various E. coli pathotypes were acquired from numerous sources, including plasmids, bacteriophages, and the genomes of other bacteria. Pathogenicity islands, relatively large (>10 kb) genetic elements that encode virulence factors and are found specifically in the genomes of pathogenic strains, frequently have base compositions that differ drastically from that of the content of the rest of the E. coli genome, indicating that they were acquired from another species.
A little-known fact is that during the genetic modification process, e-coli is used to clone the transgenic (genetically modified) DNA before it is inserted into plant cells that are then grown into transgenic crops such as those bearing the label “Roundup Ready.”
‘Genetic engineering’ or genetic manipulation as it should properly be called, relies essentially on the ability to manipulate molecules in vitro. Most biomolecules exist in low concentrations & as complex, mixed populations which it is not possible to work with effectively. This problem was solved in 1970 using the molecular biologist’s favourite bug, Escherichia coli , a normally innocuous commensal occupant of the human gut. By inserting a piece of DNA of interest into a vector molecule, i.e. a molecule with a bacterial origin of replication, when the whole recombinant construction is introduced into a bacterial host cell, a large number of identical copies is produced. Together with the rapid growth of bacterial colonies all derived from a single original cell bearing the recombinant vector, in a short time (e.g. a few hours) a large amount of the DNA of interest is produced. This can be purified from contaminating bacterial DNA easily & the resulting product is said to have been ‘cloned’.
According to Dr. Susan Bardocz, Phd during a recent conversation,
The E.coli is used as a recombinant DNA factory to produce large quantities of the transgene DNA to be used by the gene gun inserting the novel DNA into the genome of the new host, or to be inserted, as you rightly say, to Aggie [See Aggie the Traveling Agrobacterium at http://farmwars.info/?page_id=4202].
The first step is to open a plasmid in the E.coli with a molecular scizzor (Plasmids are circular geneteic elements present in bacteria) paste the transgenic DNA into the plasmid, put it back to the E.coli.
The E.coli grows in culture medium quickly, multiplies usually in every 20 mins. They harvest the DNA from the E.coli in large quantities and purify it. This purified transgenic DNA is then ready to be used for transformation.
The reason e-coli, or Escherichia coli, are used is because, like agrobacteria, which is used to insert the transgenic DNA into the plant cell during the genetic modification procedure, e-coli is highly prolific. It is also able to transfer DNA via horizontal, or lateral transfer to and from other species.
How is this significant?
New strains of E. coli evolve through the natural biological process of mutation and through horizontal gene transfer. Some strains develop traits that can be harmful to a host animal.
It is possible that a mutated form of e-coli resulting from the cloning process used in creating GMOs could get into the gut of a person or animal that eats a transgenic plant.
Could this be why DuPont, the company that produces Pioneer Hi-Bred GMO animal feed, and proud proponent of GMO technology, has jumped into partnership with the USDA in identifying hard-to-identify strains of e-coli?
A new joint project between DuPont Qualicon and the US Department of Agriculture (USDA) aims to develop testing to detect hard-to-identify strains of E.coli that are not regulated and have been causing increasing instances of food contamination.
With this convenient partnership, even if harmful strains of e-coli relating to GMOs are discovered, it is likely that the public will never hear it from the USDA or DuPont.
© 2010 Barbara H. Peterson