3-Food: More on "gut reaction"
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- Date: Mon, 22 Feb 1999 14:34:12 EST
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by Henning Strodthoff, GeN
see mail: 3-Food: genes for antibiotic resistance could jump [08.02.1999]
There is no scientific evidence for the uptake of free DNA in the gut
The Research-team at TNO showed,
- that free DNA is pretty stable in the large intestine.
- DNA from gm Tomato can reach the "safe" large intestine.
- These results suggest, that free DNA is available for uptake in
the large intestine.
- Transformation of bacteria by DNA from gm tomato in the large
was shown to be very unlikely
Bisher liegen keine wissenschaftlichen Beweise fuer die Aufnahme freier
DNA (durch Bakterien) im Darm vor. Das Forschungsteam am TNO konnte
- das freie DNA im Dickdarm relativ stabil ist.
- DNA aus gtv Tomaten kann diesen "sichern" Bereich des Darms
- Diese Ergebnisse legen nahe, das freie DNA fuer die Aufnahme durch
zur Verfuegung steht.
- Die Aufnahme von DNA aus gtv Tomaten durch Bakterien erscheint
so Jos M.B.M. van der Vossen, ein Forscher am TNO.
Die folgenden Notizen sind nach einem Gespraech mit Jos M.B.M. van der
Vossen, einem Forscher am TNO entstanden und von ihm gegengelesen.
In the following some notes from a phonecall with Jos M.B.M. van der
Vossen from TNO, who did the research with the "artificial gut" (=>
NewScientist: gut reaction)
Actually he is pretty unhappy with the articel published in the
NewScientist. Here you see what they did:
Free DNA was digested very quickly in the System (Stomach, Duodeum,
Jejunum, Ileum). After 10 sec it was no longer detectable.
Free DNA is much more stable in the "large intestine". Even after 5 to 6
min the DNA was detectable.
It was not possible to show any uptake of this free DNA by any bacteria.
Wenn they put crushed gm Tomato into the System: 5 to 10 % of the DNA
(packed in tomato-cells) passed the first part of the System (Stomach,
Duodeum, Jejunum, Ileum) and entered the "large intestine".
It was not possible to show any uptake of this DNA by any bacteria.
Untill now, it was not possible to show any uptake of DNA. So they
dicided to make a "worst case" experiment: They introduced a broad host
range plasmid into the microflora of the in vitro large intestine. In the
experiment they hoped to find bacteria that were transformed by the
They used bacteria with gm Plasmid-DNA. In the experiment they hoped to
find bacteria-to-bacteria DNA-exchange.
Even in this experiment it was not possible to show any uptake of DNA by
Therefore they analysed to what extend bacteria could be detected in this
complex ecosystem. E. coli containing a marker gene was released at
different levels in the complex flora. From this experiment it appeared
that only 1 E. coli cell could be detected among approximately 10E9
bacteria in the large intestine by using nested PCR detection.
Thus, the introduction of the broad host range plasmid resulted in a
transformation event with a rate lower than 1 / 10E9. These data
indicate that transformation of bacteria by marker genes from the
genetically modified tomato in the microflora is very unlikely. Because:
1) the marker gene needs to be integrated in the bacterial genome
2) there are no homologeous sequences available for integration
3) the marker gene lacks appropriate expression signals
So, Transformation is very unlikely.
>Gene transfer from bacterium to bacterium by conjugation:
DNA could only be transfered from bacterium to bacterium via conjugation.
This was shown in vitro as was shown previously in mice. For this, "we"
introduced the donor cells of Enterococcus faecalis containing the broad
host range plasmid pAMss1 into the in vitro large intestine together with
recipient cells. Even in the presence of a complex microflora transfer of
pAMss1 was observed with low frequency (1/10E7).
Donor cells of bacteria that are unable to grow or to compete in the
faecal flora were unable to transfer their conjugative broad host range
plasmid to the potential recipient strains.
Henning Strodthoff, GeN
enclosed the adress of
Jos M.B.M. van der Vossen, PhD
Product Manager Biomonitoring
Microbiology and Quality Management Division
TNO Nutrition and Food Research Institute
P.O. Box 360 Utrechtseweg 48
3700 AJ Zeist 3704 HE Zeist
Phone: + 31 30 69 44 720
Fax: + 31 30 69 57 901