By P Koupparis
10 May 2004

An educational biotechnology kit designed to teach students about recombinant DNA technology via hands-on experiments appeared on the market a few years ago. With one of those kits and a little cunning, anyone can run a DNA Joe Job.

Recombinant DNA technology allows a piece of foreign DNA to be inserted into a bacterium. By that means, for example, it is possible to harvest human insulin from bacteria growing in a fermentor.

The kit enables students to insert a piece of their own DNA into the ubiquitous gut bacterium Escherichia coli. It does so by using a small circle of DNA called a plasmid as the vector (i.e. delivery system).

Plasmids are found in most types of bacteria along with a single much larger loop of somatic DNA that determines the bacterium's species. A plasmid carries one or more genes that confer a survival advantage to the host, such as, for example, resistance to an antibiotic.

A bacterium can contain thousands of plasmids. Plasmids are swapped between bacteria of the same or different species. Useful plasmids propagate quickly through bacterial colonies and communities.

Bacteria also contain restriction endonuclease enzymes that cut DNA at specific sites. Ligase enzymes join such cut pieces together.

The kit exploits all of this biochemistry and includes a plasmid carrying two genes that confer resistance to the antibiotics ampicillin and kanamycin, respectively.

The resistance genes, when used with the antibiotics, enable students to identify and isolate bacteria that have taken up the modified plasmids prepared during various experiments.

The kit's capabilities bear a striking similarity to classified work carried out at places like Porton Down in England where biological weapons are developed using virtually the same techniques.

The kit allows high school students to easily perform genetic experiments that took hundreds of leading scientists using expensive and sophisticated equipment many years to research and develop. A kit costs a few dollars and fits comfortably into a pocket.

It soon became apparent that the kit also provided the means to carry out the ultimate Joe Job using DNA rather than a domain name.

Criminal DNA profiling (or fingerprinting) works by measuring the lengths of Short Tandem Repeats (STRs) found within human DNA using a process known as the Polymerase Chain Reaction (PCR). The lengths of approximately 500 STR-pair variations, known as alleles, at ten (UK) or thirteen (US) locations makes up a DNA profile. Those STR allele molecules are between 50 and 500 base pairs in length.

With access to the necessary equipment, it is possible to synthesise profiling allele molecules (custom-designed allele molecules can also be purchased online). The molecules require special "sticky ends" for the ligase enzyme to join them together. Eventually, a long strand of DNA profiling alleles (with PCR primer binding sites) is created.

Custom designed DNA molecules with the correct sticky ends can be substituted for the student's own DNA at the point in the experiment where human DNA is inserted into the plasmid. The experiment results in a culture of E. coli containing a section of DNA carrying human criminal profiling alleles. The spiked plasmids will be taken up by many other species of bacteria.

Billions of modified bacteria can then be bred in a home made fermentor. Every bacterium that acquires the modified plasmid also acquires an antibiotic resistance gene and the survival advantage it confers. Modified E. coli will swap plasmids with other species of bacteria. In the environment, STR-loaded plasmids will eventually pass to bacteria that spread via airborne spores and be blown across the planet.

Strains of bacteria carrying specially encoded DNA sequences have already been released into the environment by Porton Down scientists, who have also developed customised PCR primers to identify the tagged biological agents used in dispersal experiments.

The opportunities for mischief are endless. The full profile of a particular individual could be inserted into a plasmid thereby giving the impression that he or she was present at every crime scene contaminated with their personalised bacteria.

Random collections of human alleles can be inserted into common bacteria found in homes, on human skin and within body cavities (causing bad breath, urinary infections, etc) or in the gut of birds, rodents, flies and household pets. They would eventually become widespread and pose serious problems for agencies relying on DNA profiling to identify criminals.

Apart from human allele sequences, plasmids could be spiked with tens of thousands of modified PCR primer sequences. Contamination of crime scenes with such bacteria would tend to mask or misreport the DNA profiles of the perpetrators being sought by law enforcement agencies.

The fact that such bacteria exist (or might exist) could introduce difficulties for prosecutors and new defence arguments for those defendants against whom DNA evidence is adduced. It might also cause jurors to pause before accepting the myth of infallibility that has come to be associated with forensic DNA evidence.

The next time someone discards a cigarette butt or a used tissue, he or she could become the most famous Joe Job victim on the planet.

© Copyright P Koupparis 2004. All Rights Reserved.