Do GMO Plants Insert New Genes Into The Microbiome?

Genetically modified organisms (GMOs) are life forms that have been modified by manipulating their genetic code. In plants, animals, and bacteria, DNA makes up the genetic code: it is the blueprint for all functions for an organism. Within the genetic code, genes are the individual instructions for specific functions. While all species have a specific genetic code, modern technology can modify the genetic code by inserting genes to add certain traits to the organism. Modern agriculture has utilized this method extensively and many common foods, such as corn, soy, and milk, can be GMOs. The purpose of GMOs is to improve multiple aspects of the food industry: make crops more plentiful, make food more nutritious, or make food more stable.^[1] GMOs are typically sprayed with a variety of pesticides, fungicides, herbicides, or insecticides. While GMOs were created to improve foods, many skeptics do not buy into the supposed benefit. Opponents of GMOs argue that human selection for certain qualities in plants turns them into an “unnatural” human creation that is less nutritious and may not be safe for consumption.

GMOs are regularly eaten by consumers in the United States. Once eaten, all foods pass a group of microorganisms—largely bacteria—within the gut, called the microbiome. The microbiome is made up of over 300 trillion organisms on and within the body.^[2] The largest and most diverse microbiome on or within the human body is the gut microbiome.^[2,3] The gut microbiome is important for the synthesis of vitamins, healthy gut function, and overall health. Changes in the microbiome can have significant health impacts on individuals. Therefore, it is important to understand if ingesting GMOs can alter our microbiome and affect our health. Potential effects on the microbiome could come from two main processes: gene transfer from the GMOs to the gut microbiota, or direct effects on the microbiome from the chemicals sprayed on GMOs.

The Importance of the Gut Microbiome

There is much ongoing discussion regarding the microbiome, and for good reason. The gut microbiome is implicated in many different diseases. “Shifts” in the gut microbiome is when bacterial species fluctuate in their ratios relative to other bacterial species. The shift in the balance of gut bacteria is associated with autoimmune conditions, like Type I diabetes and inflammatory bowel disease (IBD).^[4] Within the gut microbiome, the overgrowth of one bacteria, Clostridium difficile (C. diff), can lead to a severe infection that requires medical treatment to prevent death.^[5]

The gut microbiome influences different parts of the body including the skin. The gut-skin axis is the name given to the interaction between the two systems.^[6] Maintaining a healthy gut microbiome can help improve a variety of skin conditions like eczema and psoriasis.^[6] Although there are well-known "good" foods to nourish your microbiome and “bad” foods that can harm your microbiome, GMOs do not fit solely into one of these categories. The impact of GMOs upon the microbiome is still under investigation.

Gene Transfer

The most prominent type of organism within the gut microbiome is bacteria. Bacterial genes are more mobile than human genes,^[7] allowing their DNA to be transferred from one organism to the next. The transfer of genes from one organism to another is called horizontal gene transfer.^[8] A bacterium that is resistant to antibiotics can transfer that resistance to other bacteria through horizontal gene transfer.^[9] In addition to taking up DNA from other cells, bacteria can uptake free DNA present in the environment, through a subtype of horizontal gene transfer called natural transformation.^[10]

Free DNA Within GMOs

As GMOs are consumed and broken down through digestion, GMO genes could potentially remain intact in the intestinal tract as free DNA. Few studies have been done to determine if the microbiome or body is capable of picking up free DNA from digested foods. Of those that have been completed, none of them have shown successful uptake of DNA from GMOs to bacteria within the intestines.^[11] Further studies could be improved to include the different ways that GMO DNA may be transferred within the gut, in order to provide a more realistic model.

A number of studies have been conducted on GMO crops and their potential transfer of DNA to soil or the bacteria within the soil.^[12] These studies have shown that the DNA within modified plants may linger in the soil. There are several factors that affect whether DNA sequences from GMO sources are horizontally transferred and retained in the recipient including the proportion of DNA in the GMO, integrity of DNA sequence in GMO, physical proximity of DNA from GMO and recipient, if recipient has a mechanism to uptake and incorporate DNA, and whether the GMO and recipient are genetically compatible.^[9] Some studies have shown that the soil bacteria can pick up GMO DNA in laboratory experiments but very infrequently.^[13] No studies have shown this phenomenon occurring in the environment naturally.^[13]

The Effect of Pesticides on the Microbiome

GMO's are often developed to allow the use of certain pesticides, insecticides, fungicides, or herbicides in order to increase crop production. Some studies have investigated if the microbiome is impacted by agents commonly sprayed on GMOs. It has been found that various types of toxic agents do have an impact on the GI tract in mouse studies, including reduced size of intestinal villi, altered expression of tight junction protein, increased numbers of pro-inflammatory cytokines, and lowered number of probiotic bacteria and entire bacterial flora, with an increased amount of more harmful bacteria. Interestingly, it was found that xenobiotics and the microbiota have a dualistic relationship. While the pesticide may result in significant metabolic imbalances, the bacteria respond by promoting growth of strains that assist with the detoxification of the compounds.^[14] Additional research is needed to further determine any harmful effects of pesticides and other toxic agents on the microbiome.

The Real Impact on the Microbiome

GMOs are unlikely to impact the microbiome in any meaningful way through their DNA. It is important to note that GMOs have one or two genes modified. Therefore, many of these foods are not very different from their nonmodified counterparts. No studies have shown that GMOs pose a major risk to the gut microbiome. Your microbiome likely remains safe from unwanted GMO DNA, but it is up to the consumer to choose whether or not to eat these modified foods.

Key Takeaways

1. GMOs are organisms (usually crops) that have their genetic code altered to select for favorable properties.
2. The gut microbiome is a delicate ecosystem within our body that dictates much of our health and can be affected by the things we consume.
3. The current literature does not support that consuming GMOs is harmful to our health; however, more research is needed specifically in the effects that GMOs have on the gut microbiome.