Mycotoxin production is reduced by genetically engineering Aspergillus species to delete specific proteins.
|The fungus Aspergillus nidulans (shown in this color-enhanced scanning electron micrograph) can be genetically engineered to produce fewer mycotoxins by deleting specific proteins. SCIENCE EYE/SCIENCE SOURCE
Food contaminated with fungi can be inconvenient at best and potentially fatal at worst. However, new research indicates that removing just one protein can leave some fungal toxins high and dry, which could be good news for food safety.
Some fungi produce toxic chemicals known as mycotoxins, which can not only spoil food like grains but also make us sick. One of the more dangerous types of mycotoxins, aflatoxins, can cause liver cancer and other health problems in humans.
"It is a silent enemy," says Maynooth University in Ireland fungal researcher zgür Bayram, because most people don't notice when food like corn or wheat is spoiled.
Researchers have known for years that some fungi produce these toxins, but they didn't know all the details. Bayram and colleagues have now identified a group of proteins that are responsible for activating the production of mycotoxins. The researchers report in the September 23 issue of Nucleic Acids Research that genetically engineering the fungus Aspergillus nidulans to remove even one of the proteins prevents the toxins from being produced.
"There is a long string of genes involved in the production of proteins, which will result in the production of different mycotoxins in a cascading effect," says Felicia Wu, a food safety expert at Michigan State University in East Lansing who was not involved in the research.
According to Bayram, the newly discovered proteins function similarly to a key used to start a car. The researchers wanted to figure out how to remove the key and prevent the starting signal from being sent, which would result in no toxins being produced in the first place.
Bayram and his colleagues discovered that four proteins work together to form the key in A. nidulans. The fungus was genetically modified by the researchers to delete each protein in turn. The team discovered that when any of the four proteins is missing, the key does not start mycotoxin ignition.
According to Bayram, deactivating the same group of proteins in the closely related fungus A. flavus, which can produce aflatoxins, prevents the production of those toxins. "So this is a big success because we see that the same [protein] complex does the same job in at least two fungi."
According to Wu, the new research "builds on a body of research that's been done over decades" to prevent fungal contamination of food. To control such contamination, a variety of methods are already in use. Wu explains that because not all A. flavus strains produce aflatoxins, one method of preventing contamination is to sprinkle nontoxic strains onto corn and peanut fields. These fungi proliferate and can help keep other toxic strains at bay.
This study is one of several that use genetic engineering to try to combat these toxins in food (SN: 3/10/17). One potential future application of the new research could be to genetically modify a toxin-producing fungus and then use it on crops and elsewhere. "We can basically prevent aflatoxin contamination in food, for example, in the field, even in warehouses, where there is a lot of contamination," Bayram says.
Each year, fungi and fungi-like organisms known as water molds are estimated to destroy one-third of the world's food crops. If that contamination could be avoided, Bayram estimates that the food saved would be enough to feed 800 million people by 2022.
According to Wu, the new research is a good start, but it will be a "challenge to try to understand how this can be operationalized for agricultural purposes." She says it's unclear how scalable the technique is, and getting regulatory agencies in the United States to approve the use of a genetically modified fungus on key food crops could be difficult.
B. Karahoda and colleagues The chromatin complex KdmB-EcoA-RpdA-SntB binds regulatory genes and coordinates fungal development with mycotoxin synthesis. Nucleic Acids Research, Vol. 50, p. 9797, September 23, 2022. The citation is 10.1093/nar/gkac744.