GMO Myths and Truths

acterium, thereby creating a “superbug”.
The transfer of GM genes from food to
intestinal bacteria has been documented in a
study on humans, which found that the intestinal
bacteria of a person whose diet included soy
carried sequences unique to the GM soy that was
part of their diet. 165
The second scenario in which DNA uptake by
bacteria could result in HGT of GM genes is the
transfer of GM DNA to soil bacteria. Cultivation
of transgenic crops leads to the degradation of
GM plant material in the environment, liberating
GM genes into the soil. Every cubic centimetre
of soil contains thousands of different species
of bacteria, only a small percentage of which
have been identified and characterised. Some
of the known soil bacteria can, and do, take
up free DNA that may be present in the soil,
incorporating that DNA into their genomes. 166
This could result in the transfer of GM genes
to natural soil bacterial populations. Based on
limited currently available data, this type of
event has been calculated to be extremely rare. 167
However, it has been shown that GM DNA can
persist in soil at detectable levels for at least a
year, 168 increasing the likelihood of HGT.
In addition, we only know a small fraction of
the soil bacteria that could potentially take up
DNA from their environment. 166 Furthermore,
if the uptake of a GM gene, for example for
antibiotic resistance, gives the bacterium a
survival and growth advantage, this can allow
them to outcompete other bacterial strains in the
presence of widely used antibiotics in agriculture
and medicine. Therefore, this initial rare event
could still result in a significant environmental
and health outcome. 169
5.12.2. DNA uptake during digestion
of GM foods
A study on mice demonstrated that foreign DNA
present in food can be transferred from the
digestive tract to the bloodstream of animals that
eat the food. This foreign DNA was also found in
white blood cells and in the cells of many other
tissues of the mice. 170 In a separate study, foreign
DNA in a diet fed to pregnant mice was found
in the organs of their foetuses and newborn
offspring. The foreign DNA was believed to have
reached the foetus through the placenta. 171
It has also been shown that GM DNA in feed
can be taken up in the organs of the animals that
eat it and can be detected in the meat and fish that
people eat. 172,173,174,175
Most of the GM DNA in food is fragmented
before it reaches the blood or tissues. However, a
few copies of GM DNA large enough to contain the
sequence of a full and functional gene will also be
present in the digestive tract and can be taken up
into the blood at lower frequency, where it can be
transported by the blood and taken up by cells of
some tissues or organs. 170 Once taken up by a cell,
such a GM gene could be integrated into the DNA
of the cell, causing either direct mutation of a host
gene function or reprogramming the host cell to
produce the protein for which that GM gene codes,
or both.
At present, this scenario is speculative.
Although it is clearly possible to detect transgenic
DNA in the tissues of organisms that consume
GM feed, no research has been published that
shows that the GM DNA is expressed in the
tissues of those organisms. It would be expected
that if such expression did occur, it would not
occur frequently. In order to find out whether
such expression events actually occur, it would
be necessary to conduct very large-scale studies –
though identifying a suitable experimental design
would be challenging.
It should be pointed out, however, that
although such events may be of low frequency,
because of the widespread consumption of GMOs
by both humans and animals, the fact that such
events are of low frequency does not eliminate
them as important to the biosafety assessment of
GMOs.
Though the mechanism is still unclear, GM feed
has been found to affect the health of animals
that eat it. GM DNA from soy was detected in
the blood, organs, and milk of goats. An enzyme,
lactic dehydrogenase, was found at significantly
raised levels in the heart, muscle, and kidneys of
young goats fed GM soy. 176 This enzyme leaks from
damaged cells during immune reactions or injury,
so high levels may indicate such problems.
GMO Myths and Truths 91