5.4—Transgenes are not incorporated into our bodies
Transfer of complete transgenes to bacteria in the human gut has not been demonstrated
Analysis of Peer-Reviewed Research:
Jeffrey Smith predicts dire outcomes based on the experiments reported by Trudy Netherwood. Unfortunately, Smith does not have an understanding of how promiscuous bacteria are in taking up foreign DNA. Bacteria are famous among modern biologists for their ability to take up new DNA. He is worried about expression of plant genes in gut bacteria but doesn’t realize that no whole or complete plant gene was detected in bacteria by Netherwood and colleagues. He does note that Trudy Netherwood and colleagues decided that “It is highly unlikely that the gene transfer events seen will alter gastrointestinal function or pose a risk to human health” but disagrees with their conclusions. Smith is mistaken about the main facts on which his concerns are based. Bacteria are very promiscuous in the way they capture genes from other organisms. The appearance of a plant gene fragment in gut bacteria is unremarkable and poses no new risk to human health given the capture of novel DNA is part of the normal lifestyle of bacteria that inhabit the gut. Ordinary DNA vastly outnumbers transgene DNA in our diets, so hazards of the type Genetic Roulette is worrying about are miniscule compared to the risks from dietary DNA transferring to bacteria. Consuming genes and DNA has not caused any harm for the aeons that humans have been eating food, and we have developed excellent mechanisms for coping with it.
1. Smith repeatedly imagines findings that are not in the scientific paper which he quotes. Jeffrey Smith believes that the Netherwood paper describes gut bacteria in which “the transgene was stable and appeared to produce safe herbicide-tolerant protein.” He also believes that “The bacteria were cultured in a medium containing glyphosate, the active ingredient of Roundup herbicide. The survival of the bacteria suggests that it had become “Roundup Ready,” i.e. that the transgene promoter was functioning in the bacteria and that the transgene was switched on, actively producing herbicide-tolerant protein within the human gut.” Both these claims are false. Trudy Netherwood’s article explicitly states that “It should be noted that these bacteria contained only a fragment of the [herbicide tolerant] gene, the full-length gene was not detected in these microbes.” Glyphosate herbicide was not used in their culture media for growing the microbes despite Smith’s assertion that it was.
2. Confused thinking provides a platform for scaremongering. False ideas about production of protein by gut bacteria lead Smith to scaremonger about an imagined herbicide tolerance protein in bacteria being allergenic. The small gene fragments detected in these gut bacteria by Trudy Netherwood cannot lead to production of the full herbicide tolerant protein. Readers will be reassured that there is no possibility of allergenicity when they realize that no new proteins will be produced by these bacteria. Unfortunately Smith also repeats this same confused thinking while partly contradicting himself in a later section of Genetic Roulette (Section 5.6).
3. Bacteria are promiscuous and have the ability to take in DNA from any organism. Besides getting his facts wrong about bacteria and their proteins, Jeffrey Smith is wrong in claiming that the Netherwood paper overturns “long standing assumptions that genes would not transfer to human gut bacteria”. Smith is in error by about 15 to 20 years about when these out-of date views vanished from scientific thinking. Four years before Netherwood and colleagues published their study, Howard Ochman and colleagues (Ochman and others 2000) while reviewing the remarkable bacterial mechanisms for scavenging genes from other organisms, wrote “Through these mechanisms, virtually any sequences, even those originating in eukaryotes or Archaea, can be transferred to, and between, bacteria.” In making that statement Howard Ochman was quoting references going back to at least 1991. Genetic Roulette does not reflect the rapid progress in microbiology and genetics over the last several decades. Smith’s lack of knowledge of bacterial genetics is understandable for someone with no professional training in biology, but he should have sought scientific advice from bacterial geneticists and checked his facts before making such claims in a book that purports to give advice about public health.
4. Movement of DNA fragments is certainly not a novel event in biology nor is it necessarily dangerous. The modern science of genome analysis provides abundant evidence that movement of genes and gene-fragments between species are universal features of life on earth. There is no reason to believe that movement of fragments of genes into bacteria is unique to genetically engineered DNA. Neither is there a reason to suppose that there is any tangible risk posed by gene fragments from genetically engineered DNA of plants that have been detected in bacteria. Many bacteria have ability to take up DNA from the environment, and there are numerous examples of non-transgenic DNA moving between different organisms (Citizendium 2007a, Gladyshev and others 2008, Keeling, and Palmer 2008, Koonin EV and others (2001), Ochman and others 2000). Jeffrey Smith himself quotes experiments in which such DNA fragments were detected in human tissue. The human stomach bacterium Helicobacter for instance, is well known for its ability to scavenge genes from other organisms. Given the promiscuity of bacteria in taking up DNA, it is hard to construe appearance of a soybean gene fragment in gut bacteria as a novel risk.
5. Non-transgenic foods have DNA too! Genetic Roulette’s discussion of this topic is another example of biased risk assessment where risks from transgenic DNA are considered without paying attention to similar risks already present in natural situations. The great bulk of DNA in our diets poses a far greater burden of DNA fragment traffic compared to the minor amounts of transgenic DNA present in GM crops present in our food. In transgenic maize for example, the newly introduced DNA is outnumbered by about a million-fold by pre-existing maize DNA (Thomson 2001).
Beever D and Kemp C (2000). Safety issues associated with the DNA in animal feed derived from genetically modified crops. A review of scientific and regulatory procedures. Nutritional Abstract Reviews Series B: Livestock Feeds and Feeding 70:175–182.
Citizendium (2007a). Horizontal gene transfer encyclopedia article. en.citizendium.org/wiki/Horizontal_gene_transfer accessed Dec 30 2008
de Reuse H and Bereswill S (2007). Ten years after the first Helicobacter pylori genome: comparative and functional genomics provide new insights in the variability and adaptability of a persistent pathogen FEMS Immunol Med Microbiol 50:165–176. A human stomach bacterium takes in many DNA fragments over time.
Gladyshev EA, Meselson M and Arkhipova IR (2008). Massive horizontal gene transfer in bdelloid rotifers. Science 320:1210-1213. Movement of genes across kingdoms in the ocean. You are what you eat.
Keeling PJ, and Palmer JD (2008). Horizontal gene transfer in eukaryotic evolution. Nature Reviews Genetics 9:605-618. The state of play on gene movement between different species showing that gene movement–for example between different plants that are widely unrelated to one another –has happened many times in during evolution of different organisms
Netherwood T, Martín-Orúe SM, O’Donnell AG, Gockling S, Graham J, Mathers JC and Gilbert HJ (2004). Assessing the survival of transgenic plant DNA in the human gastrointestinal tract. Nature Biotechnology 22(2):204-209. Transgene DNA is digested to small fragments in the human gut. Some fragments can be detected apparently associated with gut bacteria. Intact full length genes were not detected. No transgene fragments can be detected in faeces.
Ochman H, Lauwrence JG and Grolsman EA (2000) Lateral gene transfer and the nature of bacterial innovation. Nature 405: 299–304 Bacteria are promiscuous. “Through these mechanisms, virtually any sequences, even those originating in eukaryotes or Archaea, can be transferred to, and between, bacteria.”
Koonin EV, Makarova KS and Aravind L (2001). Horizontal gene transfer in prokaryotes:Quantitation and classification. Annual Review of Microbiology 55:709-42.
Thomson J (2001). Horizontal transfer of DNA from GM Crops to bacteria and to mammalian Cells. Journal of Food science 66(2):188-193.
van den Eede G and others (2004). The relevance of gene transfer to the safety of food and feed derived from genetically modified (GM) plants. Food and Chemical Toxicology 42:1127–1156
1. The only human feeding trial ever published confirmed that genetic material from Roundup Ready soy transferred into gut bacteria in three of seven human volunteers.
2. The transferred portion of the transgene was stable inside the bacteria and appeared to produce herbicide-tolerant protein.
3. There is no known way to treat such a condition, which may be long-term.
Genetic Roulette describes experiments that were undertaken by Trudy Netherwood and colleagues (Netherwood and others 2004) to monitor stability and movement of DNA from transgenic soybeans included in the diet of human volunteers. These experiments failed to detect gene movement.