Expert response from Dan Goldstein
Former Senior Science Fellow and Lead, Medical Sciences and Outreach, Monsanto Company
Tuesday, 24/02/2015 10:20
I have been fascinated by this issue since my days in undergraduate statistical genetics. I assume you want to know about what occurs ‘in the wild’ and the most well-known example is viruses moving DNA to their host cells. But you are probably interested in non-viral transfer.
There are specialized situations in which genetic exchange can, and have, occurred among higher organisms (plants); primarily related to close symbiotic relationships. Genomic studies have found a few examples of probable transfer of bacterial genes to higher species, but these are rare events that occur on an evolutionary time frame. The best example (excluding viral infections which routinely transfer genetic material) is Agrobacterium tumifaciens. This bacterium routinely transfers genetic material into plants and is used to insert genes in the development of GM crops.
In higher organisms the phenomenon is limited by factors other than just DNA uptake. If DNA can make it into a cell, it must integrate successfully and in a functional form (otherwise it just sits there), the cell must remain with the organism (we replace gut cells every three days or so) and the gene must be incorporated into reproductive cells (ova or sperm) in order to transmit between generations. Because of major barriers such as: 1) the uptake of DNA at the organism level (digestion); 2) recognition and destruction of foreign DNA at the cellular level; and 3) genetic transmission and gene dissemination, it is little surprise that such events are rare in free-living organisms lacking special factors like symbiosis. If you are willing to wait around for a half a billion years or so, unpredictable and exceedingly rare events can occur.
Perhaps what you are most interested in is transfer of DNA from food to mammals. I am not aware of any food to mammal transfer. All whole-foods (i.e. not highly processed foods such as sugar and oil) contain large amounts of DNA and GM crops do not differ from conventional or organic crops, they all contain DNA, which DNA is like the rest of DNA, and would not differ in respect to such transfers.
Gene transfer from gut bacteria or from food into the mammalian genome has never been documented in real time (i.e. observable time - not on an evolutionary time scale). This has been searched for repeatedly, and indeed small FRAGMENTS of feed-derived DNA (parts of genes) can be found in some tissues of animals. While they used GM DNA as one of the markers, both GM and non-GM DNA fragments can be found, especially if one either looks for shorter fragments or for fragments coming from genes with more copies per cell (mitochondrial or chloroplast genes). These are not incorporated in any way into the genome… just bits and pieces of DNA. Some of this phenomenon represents normal functions of the immune system in higher animals.
It is clear that higher organisms have developed robust mechanisms to prevent foreign DNA from routinely invading the genome. Prokaryotic organisms are prolific mutators and are more of a genetic continuum than a set of defined species, but the higher eukaryotes are well defined- there are heffalumps and woozles which don’t mix (in the absence of symbiosis) and clearly do not pick up genetic material from their surroundings in a “real time” framework relevant to food or feed safety.
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