A study that fed high concentrations of Bt corn to pigs for long periods did not detect any rDNA or recombinant proteins in the blood of sows or the blood, heart, kidney, spleen, or muscle of their offspring at birth Buzoianu et al. To date, no studies have identified rDNA fragments in meat or visceral organs from chickens. However, similar to the aforementioned species, some studies have detected fragments of endogenous plant genes Table 2.
Because endogenous plant-specific DNA sequences are not found in chicken embryos, it is likely that any endogenous plant gene fragments that are detected are transferred from feed to the animal Klotz et al. Studies in quail have also failed to identify rDNA fragments in samples from muscle and internal organs Flachowsky et al. A study that aimed to investigate the presence of DNA fragments in tissues from rabbits fed GE soybean meal identified only chloroplast DNA and was not able to detect the endogenous lectin gene or the cauliflower mosaic virus 35S CaMV 35S promoter present in the GE soybean Tudisco et al.
Another study similarly failed to detect GE-feed-derived genes in leg muscle samples from rabbits fed transgenic poplar leaf pellets Yang et al. Similarly, dietary DNA fragments detected in fish have not been large enough to code for functional proteins Table 2.
A study investigating the fate of transgenic sequences from GE soybean during Atlantic salmon feeding experiments failed to amplify any soy DNA fragments conventional or GE in liver or muscle Sanden et al.
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A later study in Atlantic salmon conversely identified endogenous rubisco DNA fragments of soybean and maize origin in various tissue samples but did not detect any rDNA Wiik-Nielsen et al. Studies assessing the use of GE soybean meal in feed for rainbow trout Chainark et al. Collectively, these studies have failed to identify full-length endogenous or rDNA transcripts or recombinant proteins in meat. Milk is an important and popular food due to its nutritional value and is a subject of food safety studies due to the vulnerability of its primary consumers, children.
Several studies have investigated the potential transfer of DNA from feed to milk. To date, whole transgenes have not been detected in milk from cows or goats Table 4 , although endogenous plant DNA fragments have been detected in some instances Einspanier et al.
One report from Italian market samples found very small fragments of rDNA due to environmental contamination Agodi et al. Phipps et al. However, small fragments of the high copy endogenous corn gene rubisco were detected in the majority of milk samples Phipps et al. Similarly, Einspanier et al. Castillo et al.
Singhal et al. Yonemochi et al. A study using a small number of Simmental cows failed to identify DNA transfer from feed containing soy and maize non-GE into milk Poms et al.
It was concluded that the presence of the transgenic sequences was likely due to fecal or airborne contamination of feed or feed particles or other environmental contamination. This is supported by results from a study in which raw milk was left exposed in the cow shed, and airborne soy and maize feed contamination was detectable when placed up to 10 m away from the feeding site Poms et al. In their conclusions, the authors support the assertion that there is no inherent risk in consuming DNA, including DNA from transgenic crops Agodi et al.
rersimaper.ga A later study of plant diet contents in raw cow milk samples from the Italian market and stock farms detected endogenous chloroplast genes in total milk as well as skimmed and cream fractions Ponzoni et al. A study testing for GE plants in milk and dairy products commercially available in Greece, including yogurt and cheese, failed to identify any rDNA fragments Paramithiotis et al.
A study Hassan and Ali, reported the detection of a bp fragment of the NOS-terminator sequence in 3 of 7 imported dried milk powder samples purchased from a market in Iraq. Unfortunately, there are few details on the origin of these milk samples except that 1 of the positive samples, Dielac, was identified as being from New Zealand. That sample had a positive band when amplified with primers designed to the NOS-terminator. New Zealand tends to have a pastoral dairy production system and does not grow GE crops.
They do import a small amount of maize and soy Fig. However, the authors of this paper did not follow the good laboratory practice of including the amplification of abundant endogenous plant DNA sequences e. Given that the results of this paper disagree with the many published studies that show no presence of rDNA fragments in milk, these controls would have helped support the validity of the results presented. This report appeared in the Journal of American Science , published by Marsland Press, which has appeared on Beall's List of Predatory Publishers Beall, since , casting further doubt that this paper underwent rigorous peer review.
In , a controversial and subsequently retracted paper claimed to have identified rDNA fragments in milk from goats fed GE soybean in Italy. The report also claimed that small fragments of rDNA were detected in tissues and organs of goat kids whose dams had consumed GE soybeans. The authors noted that the results conflicted with published results from other studies. A study by the same authors also claiming significant detection of transgenic fragments in liver and kidney from goat kids fed milk from dams that consumed GE soybean meal was also retracted for fraud due to data fabrication, and the results were declared to be invalid Mastellone et al.
A third paper from this group, citing similar issues with GE soybean meal and likewise containing digitally manipulated images Tudisco et al. Unfortunately, these retracted studies in journals published by predatory publishers continue to be cited by groups opposed to GE, and these falsified data are used to incorrectly suggest there is a distinguishable difference between milk derived from animals that have been fed GE feed compared with those that were not.
The weight of evidence from numerous well-controlled, peer-reviewed papers does not support this conclusion, because rDNA fragments cannot be reliably or repeatedly detected in the milk from animals that have consumed GE feed. Similar to meat and milk, eggs are primary sources of protein, fats, and micronutrients in the human diet. Because eggs are relatively inexpensive and easy to handle and store, they provide important nutrition for consumers in both developed and developing countries NRC, Eggs contain only a small amount of DNA Aeschbacher et al.
In , Einspanier and colleagues reported that they did not detect any foreign plant DNA fragments in eggs from chickens fed diets containing conventional or recombinant Bt maize, despite that chloroplast DNA was reliably detected in chicken organs Einspanier et al. A report detected no transgenic or endogenous plant DNA fragments in eggs from hens fed diets containing both insect-resistant maize MON and GE herbicide-tolerant soybean Swiatkiewicz et al.
Ash et al. A long-term feeding study in quail, in which 10 generations of birds consumed diets containing Bt corn, did not detect rDNA fragments in eggs after the initial wk feeding period and also not after 1 yr of feeding Bt corn. A subsequent study evaluating 4 generations of quail fed diets containing GE soybean meal and maize grain also did not detect rDNA in eggs from test animals Korwin-Kossakowska et al.
All studies to date have failed to amplify endogenous or rDNA or recombinant protein from feed in eggs Table 5 , suggesting that eggs from poultry fed GE feed are indistinguishable from those fed non-GE feed, given the available data. One of the main concerns voiced by the public is that DNA from GE crops could be taken up by bacteria in the gut of food animals or humans.
In mammals, the main point of entry of foreign macromolecules is the gastrointestinal tract Rizzi et al.
The human intestine is estimated to harbor more than 10 14 microorganisms from thousands of different bacterial species Aron-Wisnewsky and Clement, The successful transfer of genetic information by horizontal gene transfer is dependent upon a number of criteria and the completion of several steps. In order to result in a complete gene that could potentially be expressed, the incorporated DNA would have to be largely intact. As discussed, once food and feed have been processed and are consumed, the DNA is most often fragmented into small pieces, regardless of whether it is GE or not.
Overall, lower uptake efficiency has been observed with shorter fragments van den Eede et al. In addition, the further species are from one another on the phylogenetic tree, the fewer sites are available for homologous recombination Jonas et al. In addition to the low likelihood that large full-length DNA fragments would be present in the gastrointestinal tract for horizontal gene transfer to occur, any fragments that were present would have to compete with the rest of the digested DNA, potentially from multiple dietary sources, for transfer into a bacterium, because the process is not sequence specific.
Expression of transgenes by gut bacteria would also be contingent upon the simultaneous transfer of regulatory elements, such as promoters, in the proper orientation and context Thomson, The physiology of the recipient cell would also play a role in whether transferred DNA is expressed, including the compatibility of its transcription and translation machinery with the signals of the incoming DNA Jonas et al. In the extremely remote instance an intact gene was taken up, it is highly unlikely that it would be advantageous in the absence of selective pressure for the encoded protein Thomson, A number of animal feeding studies have shown no changes in intestinal bacteria in food animals as a result of consumption of feed with GE ingredients based on DNA sequencing.
Buzoianu et al. A subsequent study by the same group further confirmed the absence of adverse effects of Bt maize on porcine intestinal microbiota across generations of sows and their offspring Buzoianu et al.
Similarly, no adverse effects on intestinal microflora in broilers were observed after consuming diets containing GE herbicide-tolerant soybean meal Tan et al. In a study using Holstein-Friesian cows, quantitative changes in ruminal bacterial communities were analyzed by real-time PCR, and the authors concluded that diversity in microbial populations depends more on the individual animal and the sampling day than it does on the type of maize used to produce the silage consumed Wiedemann et al.
Other studies of the effects of diets containing transgenic corn on cow rumen in vivo similarly revealed no overall impact on rumen microbiota Einspanier et al. A 3-yr longitudinal study of consumption of Bt maize in sheep likewise showed no differences and revealed no evidence of horizontal gene transfer to ruminal microorganisms or animal tissues Trabalza-Marinucci et al. Additionally, although several bacterial species are capable of acquiring external DNA by natural transformation, bacterial uptake of dietary DNA in vivo in the intestine has not been detected to date Rizzi et al.
Most of the studies that have investigated horizontal gene transfer of recombinant plant DNA have been under optimized conditions, and all of these studies have yielded negative results unless the recipient bacterial strains were genetically modified to facilitate integration of recombinant plant DNA by homologous recombination EFSA, Horizontal gene transfer from plant to animal genomes is at most very infrequent. Gene loss during animal evolution cannot be ruled out as an explanation for the rare examples that have been proposed.
In eukaryotes, horizontal gene transfer seems to be associated mainly with single-celled protists, especially those that engulf their food, or in multicellular organisms with parasites in close cellular contact with their hosts.