Ethiopia goes organic to feed herself - The Institute of Science In ...

36
denum of cattle. The studies were variable in
quality, depending especially on the sensitivity
of the PCR methodology used to amplify
specific sequences for detection.
Nevertheless they suggest that GM DNA
can transfer to bacteria within the rumen and
in the small intestine. In neither sheep nor
cattle was feed DNA detected in the faeces,
suggesting that DNA breakdown may be
complete by then.
The only feeding trial in human volunteers
was perhaps the most informative.
After a single meal containing GM soya containing
some 3x1012 copies of the soya
genome, the complete 2 266 bp epsps transgene
was recovered from the colostomy bag
in six out of seven ileostomy subjects (who
had their lower bowel surgically removed).
The levels were highly variable among individuals
as quantified by a small 180bp PCR
product overlapping the end of the cauliflower
mosaic virus (CaMV) 35S promoter
and the beginning of the gene: ranging from
1011 copies (3.7%) in one subject to only 105
copies in another. This is a strong indication
that DNA in food is not sufficiently rapidly broken
down in transit through the gastrointestinal
tract, confirming the results of an earlier
experiment by the same research group.
No GM DNA was found in the faeces of
any of 12 healthy volunteers tested, suggesting
that DNA has completely broken down,
or all detectable fragments have passed into
the bloodstream (see later) by the time food
has passed through the body. This finding is
in agreement with the results from ruminants.
In general, the studies report that GM
DNA degrades to about the same extent and
at about the same rate as natural plant DNA.
However, no quantitative measurements
have been made, and GM DNA was often
compared with the much more abundant
chloroplast DNA, which outnumbers the
transgene by 10 000 to one.
3. Is GM DNA taken up by bacteria and
other micro-organisms?
The answer is yes. The evidence was reported
in the human feeding trial mentioned. The
transgene was not detected in the contents
of the colostomy bag from any subject before
the GM meal. But after culturing the bacteria,
low levels were detected in three subjects out
of seven: calculated to be between 1 and 3
copies of the transgene per million bacteria.
According to the researchers, the three
subjects already had the transgene transferred
from GM soya before the feeding trial,
probably by having eaten GM soya products
unknowingly. No further transfer of GM DNA
was detected from the single meal taken in
the trial.
The researchers were unable to isolate
the specific strain(s) of bacteria that had
taken up the transgene, which was not surprising,
as "molecular evidence indicates that
90% of microorganisms in the intestinal
microflora remain uncultured. …they can
only grow in mixed culture, a phenomenon
seen with other microorganisms."
Actually, GM DNA can already transfer to
bacteria during food processing and storage.
A plasmid was able to transform Escherichia
coli in all 12 foods tested under conditions
commonly found in processing and storage,
with frequencies depending on the food and
on temperature. Surprisingly, E. coli became
transformed at temperatures below 5
degrees C, i.e. under conditions of storage of
perishable foods. In soy drink this condition
resulted in frequencies higher than those at
37 degrees C.
4. Do cells lining the gastrointestinal
tract take up DNA?
The answer is yes. Food material can reach
lymphocytes (certain white blood cells) entering
the intestinal wall directly, through Peyer's
patches. And fragments of plant DNA were
indeed detected in cows' peripheral blood
lymphocytes.
It is notable that in the human feeding
trial, a human colon carcinoma cell line
CaCo2 was directly transformed at a high frequency
of 1 in 3 000 cells by an antibiotic
resistance marker gene in a plasmid. This
shows how readily mammalian cells can
take up foreign DNA, as we have pointed out
some years ago (see also below).
5. Does DNA pass through the gastrointestinal
tract into the bloodstream?
The answer is yes, as mentioned above,
fragments of plant DNA were detected in
cow's peripheral blood lymphocytes.
However, attempts to amplify plant DNA fragments
from blood have failed, most likely on
account of the presence of inhibitors of the
PCR amplification.
6. Does DNA pass into milk?
The official answer from the UK Food
Standards Agency is no, based on a single
study it commissioned that was practically
worthless (see "Exposed: More shoddy science
in GM maize approval", SiS 22). The
researchers tested DNA from 333 microlitres
of milk - about 3 drops - using a PCR detection
method that required the equivalent of
4059 copies of the GM soya genome and
905 copies of the maize genome to give a
positive signal.
Recently, Greenpeace in Germany published
the results of a study from the
Research Centre for Milk and Foodstuffs in
Weihenstephan, Bavaria, which was reportedly
"kept under lock and key for three
years". It contained the results of a farmer's
milk samples that tested positive for GM
DNA from Roundup Ready soya and Bt176
maize. The researchers pointed out that the
GM DNA fragments might have found their
way into milk via GM feed given to the animals
that produced the milk, or else via dust
from GM plants contaminating the milk.
7. Is DNA taken up by tissue cells?
The answer is yes, and this has been known
since the mid 1990s. GM DNA and viral DNA
fed to mice ended up in cells of several tissues,
and when fed to pregnant mice, the
DNA was able to cross the placenta, and
enter the cells of the foetus and the newborn.
These results were confirmed in 2001, when
soya DNA, too, was found taken into the tissue
cells of a few animals.
In general, abundant chloroplast
sequences have been detected in the tissues
of pig and chicken but not single gene
DNA nor GM DNA. But rare events are most
likely to go undetected, on account of the limitations
of the PCR technique.
Recently, "spontaneous transgenesis" -
the process of spontaneous uptake of foreign
DNA resulting in gene expression - has been
rediscovered by a team of researchers looking
for new possibilities in gene therapy. They
documented the phenomenon in several
human B lymphocyte cell lines as well as
peripheral blood B lymphocytes. The transgene
in a plasmid was readily taken up and
was found in many cell compartments including
the nucleus, where gene transcription
took place. The plasmid was not integrated
into the genome, but the researchers say that
its eventual integration cannot be ruled out.
8. Is GM DNA more likely to insert into
genomes?
This is perhaps the most important question.
There are reasons to believe GM DNA is
more likely to insert into genomes after it is
taken up into cells, chief among which, its
sequence similarities (homologies) to a wide
variety of genomes, especially those of viruses
and bacteria. Such homologies are
known to enhance horizontal gene transfer to
bacteria up to a billion fold.
More significantly, the integration of nonhomologous
genetic material can occur at
high frequencies when flanked by homologous
sequences. A recent report highlights
the importance of this "homology-facilitated
illegitimate recombination", which increases
the integration of foreign (non-homologous)
DNA at least 105 fold when it was flanked on
one side by a piece of DNA homologous to
the recipient genome.
No experiment has yet been done to
assess whether GM DNA is more likely to
transfer horizontally than natural DNA.
However, in the human feeding trial, where
three ileostomy volunteers tested positive for
the soya transgene in the bacteria cultured
from their colostomy bag, the soya lectin
gene Le was not detected in the bacterial cultures
from any of the subjects.
The researchers found it necessary to
remark, "Although the plant lectin gene was
not detected in the microbial population…it is
premature to conclude that the epsps transgene
is more likely than endogenous plant
genes to transfer into the microbial population."
But until this possibility has been adequately
addressed, it cannot be ruled out. SiS
SCIENCE IN SOCIETY 23, AUTUMN 2004