Countering mycotoxins with bacteria and enzymes

The presence of mycotoxins in agricultural com­modities is spreading worldwide in recent years. Wheat growers and producers around the globe acknowledged the spreading of deoxynivalenol problem while simi­lar concerns were raised by corn producers during the 2013-2014 harvest seasons.

Climate changes causing increased mycotoxin concerns

Recently witnessed climate changes around the globe are causing greater mycotoxin contamination concerns. The reported changes influence host-pathogen interactions in addition to how pathogens respond to the surrounding environmental conditions. Higher temperatures in summers are increasing incidents of fungal diseases associated with crops and the severity/persistence of such diseases. Furthermore, genetic mutations in different fungal species that affect mycotoxin levels within the infected kernels have been reported and the new fungal populations are spreading with unpredictable rates and long-term consequences. Significantly higher levels of aflatoxins (AF), deoxynivalenol (DON), fumonisins (Fum), ochratoxin A (OTA), and zearalenone (ZEA) are being detected in wheat and corn-based commodities.

Adopting lower mycotoxin limits agriculture

The increased body of knowledge about the adverse effects connected with the accidental consumption of mycotoxins either by humans or animals ascertains the importance of implementing more rigorous regulations to avoid even trace amounts of these fungal-secondary metabolites in our food chain. Regulatory bodies around the world are in favour of adopting lower limits of mycotoxins for agricultural products, posing even greater challenges to growers, food producers, and international trade. An example is the two parts per million (ppm) maximum levels of DON proposed at farm-gates by the US Food and Drug Administration (FDA) and the European Union (EU).

Early detection and elimination of mycotoxin-contaminated corn/wheat has proved inadequate when used alone and effective post-harvest methods to prevent mycotoxins from entering the food/feed chains are in high pursuit. The thermal/chemical stability of mycotoxins (DON is a good example) makes conventional methods of processing impractical for inactivating mycotoxins.

Microbial strategies to control mycotoxins

While there are some encouraging interventions developed recently aiming at addressing mycotoxin contamination such as the irreversible binding of mycotoxins to clay or specific polymeric compounds, the biological detoxification looks to be a very promising alternative due to its specificity, acceptance by consumers, and possible utilisation under mild processing conditions. Bacteria, yeasts, and enzymes obtained naturally from different domains of life can potentially be employed in reducing mycotoxins levels to an acceptable range before further processing or handling of food/feed ingredients.

Many research teams around the globe were involved in exploring environmentally-friendly and cost-efficient methods to combat fungal infections/spoilage and control mycotoxin contaminations in food and feed during the past three decades. A plethora of reports describing the isolation of bacterial species or strains that can bio-transform mycotoxins and substantially reduce their toxicities have emerged.
Throughout the years, many different bio-niches were explored to identify bacterial strains that have the ability to detoxify mycotoxins and diminish their bio-toxicity. The earlier focus was on bacteria obtained from the digestive tracts of farm animals or at least has the ability to colonise these tracts. These approaches were partially successful and led to the isolation of some promising anaerobic bacterial species such as Genus novus strain BBSH 797 and Bacillus arbutinivorans Strain LS-100 that can convert DON to the deepoxy-deoxynivalenol (DOM-1) metabolite within the animal gut and reduced its biological toxicity.

Successful isolation of novel bacterial strains

The current trend is to isolate bacteria that can bio-transform mycotoxins under aerobic conditions and mild temperatures (25-300C) and in the presence of a wide range of organic sources of nitrogen and carbon ahead of the actual consumption. Efforts over the past five years have led to the successful isolation of novel bacterial strains belonging to the Devosia genus, such as Devosia mutans Strain 17-2-E-8 originating from a Canadian agricultural soil sample and has the capability to modify DON molecule at the C3 position, hence detoxifying the mycotoxin under more practical feed processing conditions and before the toxin enters the animal alimentary canal. The abrogation of toxicity was confirmed using different human cell lines and mouse models and is predicted to result from the isomeric changes that influence 3-epi-DON ability to form hydrogen bonds within the peptidyl transferase center of ribosomes. Furthermore, the recent technological advances in microbiology, mycology, molecular biology including next-generation sequencing of bacterial genomes; the enhanced analytical capabilities of LC-MS/MS platforms; and the 
production of recombinant DNA/proteins are all promising to revolutionise the way we combat mycotoxins.

Alternatives for addressing mycotoxin contamination

More than 5000 different enzymes are currently known, many of which have been characterised and found their ways to industrial applications. While we are far away from covering the 400 different known fungal metabolites/mycotoxins with an enzymatic detoxification solution for each one, targeting the most detected mycotoxins in cereals is surely considered as a good start (see Table 1) and will definitely influence the way we address mycotoxin contamination in the future. New enzymatic solutions for targeting mycotoxins have started to emerge with some already commercially-available for farmers around the world. Enzymes that can inactivate FUMs are now available on the market while enzymes with the potential for inactivating DON and ZEN are awaiting commercialisation.

The collection of accurate data regarding weather patterns, fungal infestation, and mycotoxin contamination is becoming an increasingly high priority. This pivotal data will help in developing rigorous and reliable models to forecast the effects of climate changes on mycotoxin contamination. Such models can aid in understanding the recently detected patterns of fungi-spreading and possibly provide the necessary foresight for strategic adaptation to climate changes. Our enhanced understanding of mycotoxins, environmental factors that influence their presence in cultivated crops, and their mode of toxicity coupled with the latest state-of-the-art experimental methods are being empirically utilised nowadays to pan out enzymes/mechanisms involved in detoxification pathways. Together this accelerates the discovery of bioremediation methods that can potentially address many of the concerns related to mycotoxin contamination. The industry’s willingness to adopt new enzymatic solutions and other related technologies will be a leading factor at the forefront of the efforts to combat the spread of mycotoxins in agricultural commodities.