Using Population Genomics to Quantify Mycotoxin Chemotypes in Our Food Crops
Many of the foods and beverages we eat daily, including yogurt, fries, beer, and sourdough bread, contain small living organisms’ unseen by the eye. Some of these organisms, such as those in yogurt and kombucha, are considered good for our health. However, not all microorganisms are good for our health, such as the fluffy, pink fungus Fusarium graminearum. Let’s call it F. gram. Food contamination can occur in various parts of production from the crop itself, during storage, or if contaminated grains are fed to livestock. At some point in our lives we have all eaten something with a harmful organism; maybe you had no reaction, or you might have had a bad case of food poisoning. F. gram produces three kinds of mycotoxins, toxic chemicals produced by fungi, that contaminate our food and cause illness from poisoning, damage to our immune system, and even cancer. Symptoms of ingestion can include vomiting, headache, and fainting.
The three kinds of F. gram mycotoxins are colloquially known as NA1, NA2, and NA3. This article focuses on one of these mycotoxins, NA3. We don’t know its background, when it first arose, or how.
Plant pathologists and farmers noticed more disease and mold on crops in the past decade and were invested in finding the cause. A study using population genomics found the NA3 strain was responsible for this damage that is killing more crops. By identifying the parts of the NA3 genome causing virulence (its ability to infect crops) they found the ratio of crop infection by the three strains, which genes were transmitted by natural selection, and which parts of the genome were most hazardous in NA3. They confirmed that NA3 toxin is of a different evolutionary origin, not a combination of NA1 or NA2 as hypothesized. Author Dr. Todd Ward predicts that “based on the available data, I would expect to see continued gene flow between the populations where they occupy the same geographic areas, and this could lead to exchange of adaptations among the populations. It is not clear what this would mean for pathogen specialization or range expansion, but as a species, F. graminearum already has a very wide geographic distribution.”
The fungus that produces NA3 grows best in warm, humid conditions. Many regions, including the Maritimes, are becoming warmer and more humid because of climate change, resulting in the expansion of the NA3 infection range. That, coupled with crop exportation around the world, means the proportion of crops infected is likely to increase.
Locally in the Maritimes, NA3 is found in many crops such as barley, wheat, potatoes, and other varieties of cereal crops. There is no doubt that NA3 has made its way into our French fries, baked potatoes, bread, beer, and other popular food products. As students, we have enough to think about without worrying about what’s in our beer and late-night fries.
Research has shown that NA3-contaminated grain used in bread-making was a real threat to consumers. Only 50% of the toxin was reduced to a non-toxic level after the bread was baked. Given the very limited regulations on mycotoxin levels (including NA3), this amount is troublingly high. Fortunately, the threat of this toxin can be reduced through targeted fungicides and proper seed storage. This study answered the first of several questions regarding the NA3 population, although Dr. Ward says that “the results of the 2018 study have generated numerous new areas for additional research. Some recent publications from the USDA team in Peoria have specifically focused on understanding if NX toxins are a virulence factor, like other trichothecenes, required for spread beyond the initial point of infection in wheat (they are) and determining if the NA3 population is as aggressive as the NA1 and NA2 populations on moderately resistant wheat (it isn’t).”
Population genomics has proven to be a revolutionary molecular biology technique to answer the increasingly important questions connected to food safety, human health, and the impact of our changing climate on both. This means we need new specialized technology and universities, like Mt. A, to support the development of skilled genome scientists and pathologists in the upcoming generation to meet these challenges.
For more information, check out “Population genomics of Fusarium graminearum reveals signatures of divergent evolution within a major cereal pathogen” by Kelly and colleagues (2018). https://doi.org/10.1371/journal.pone.0194616