How could micro-organisms reduce mycotoxins in cereals?

Wheat is often infested with harmful moulds, including those that can form toxins known as mycotoxins. This project investigated the effectiveness of microorganisms that naturally degrade the mycotoxin zearalenone (ZEN). Tests showed that Bacillus strains reduce ZEN more efficiently than lactic acid bacteria. Under optimum conditions, an almost complete reduction was achieved within six hours. The degradation mechanism will be researched further in follow-up projects.

Translated with DeepL

The overall aim of the BioDeTox project was to evaluate the efficacy of microorganisms in reducing the concentration of zearalenone (ZEA) and to investigate the mechanism of ZEA reduction in selected strains. In addition, the optimal fermentation conditions for ZEA reduction were to be analysed.

Analysis of the efficacy of 42 Bacillus strains (B. megaterium, B. licheniformis, B. subtilis, B. pumilus) and 11 strains of lactic acid bacteria (MSB; L. brevis, L. parabuchneri) showed that the tested bacilli were significantly more effective at reducing ZEA than the MSB. The MSB reduced ZEA by 30–50% after 24 h of incubation in liquid medium and by 30–80% after 48 h, with L. brevis MA278b (80% reduction) and L. brevis JR114 (75% reduction) being the most efficient. The bacilli reduced ZEA by at least 30% after only 14 hours of incubation. Particularly efficient were B. licheniformis MA695, TR082, TR206, TR212, TR251b, TR374 and B. megaterium Myk108 and Myk133, with a reduction of over 90%. B. megaterium Myk108 showed the highest reduction (97%).

To investigate the mechanism of ZEA reduction, the eight most effective Bacillus strains and two best MSB strains were tested and ZEA was added to the living cells, cell-free supernatant, cell extract and cell wall debris and analysed after 72 h. A reduction of ZEA by the cell-free supernatant indicated the influence of extracellular enzymes, a reduction by the cell extract the influence of intracellular enzymes, and a reduction by the cell wall debris the binding of the mycotoxins.

The living cells of all strains reduced ZEA by 90–100% after 72 hours of incubation. Bacilli were more efficient than MSB. Interestingly, the cell wall debris of MSB reduced 50–70% of ZEA, but with bacilli only 10–20%. This indicates that MSB reduce ZEA mainly by binding, while with bacilli only a small proportion is bound and a degradation mechanism is suspected. However, the cell-free supernatant and the cell extract did not lead to a significant reduction in ZEA content in any strain (MSB and bacilli), which indicates the absence of active enzymes, intracellularly and/or extracellularly. This contradicts the current literature, where studies have shown enzymatic degradation of mycotoxins in bacilli.

Using B. megaterium Myk108 as the most effective strain, optimal conditions for ZEA reduction were determined. pH values of 6, 7 and 8 and temperatures of 25°C, 30°C, 37°C and 42°C were tested. Almost complete reduction of ZEA was achieved after 6 h incubation at 37°C and 42°C and pH 6.

In summary, the results show that bacilli enable more effective ZEA reduction than MSB. While MSB mainly bind ZEA, the degradation mechanism of bacilli remains unclear. The highest reduction rates were achieved with B. megaterium Myk108 under specific conditions, making this strain promising for applications in mycotoxin reduction. The exact mechanism of ZEA reduction in bacilli could not be elucidated in the present project and is subject of further research.