Mycoviruses Increase the Attractiveness of Fusarium graminearum for Fungivores and Suppress Production of the Mycotoxin Deoxynivalenol

RNA viruses of the genera Ambivirus, Mitovirus, Sclerotimonavirus, and Partitivirus were found in a single isolate of Fusarium graminearum. The genomes of the mitovirus, sclerotimonavirus, and partitivirus were assigned to previously described viruses, whereas the ambivirus genome putatively represents a new species, named Fusarium graminearum ambivirus 1 (FgAV1). To investigate the effect of mycoviruses on the fungal phenotype, the spontaneous loss of mycoviruses during meiosis and the transmission of mycoviruses into a new strain via anastomosis were used to obtain isogenic F. graminearum strains both with and without mycoviruses. Notable effects observed in mycovirus-harboring strains were (i) the suppression of the synthesis of trichothecene mycotoxins and their precursor trichodiene, (ii) the suppression of the synthesis of the defense compound aurofusarin, (iii) the stimulation of the emission of 2-methyl-1-butanol and 3-methyl-1-butanol, and (iv) the increased attractiveness of fungal mycelia for fungivorous collembolans. The increased attractiveness of mycovirus-infected filamentous fungi to animal predators opens new perspectives on the ecological implications of the infection of fungi with viruses.

Effects of temperature and soil fauna on the reduction and leaching of deoxynivalenol and zearalenone from Fusarium graminearum-infected maize stubbles

A microcosm study was conducted at two different temperatures under laboratory conditions to investigate the regulatory capacity and the interactive performance of two soil fauna species (Aporrectodea caliginosa, earthworms, and Proisotoma minuta, collembolans) on the reduction of Fusarium toxins in contaminated maize stubbles. Single and mixed species treatments were exposed to artificially infected maize stubbles highly contaminated with the mycotoxins deoxynivalenol (DON) (10,462 µg kg⁻¹) and zearalenone (ZEN) (2,780 µg kg⁻¹) at 17 °C and 25 °C for time periods of 3 and 6 weeks. Immediately after the respective end of incubation, the microcosms were heavily watered to determine the leaching potential of DON and ZEN from contaminated maize stubbles. Maize residues, soil, and eluted water (percolate) samples were analysed for mycotoxin content using liquid chromatography coupled to mass spectrometry. The biomass of introduced earthworms and number of collembolans were monitored to get information about their adaptability to the experimental conditions. While the decline of ZEN was temperature-dependent, but not influenced by faunal activities, a reduction of DON due to faunal impact was observed by trend. In the leaching experiment, 67–82% of the DON content in the residual maize stubbles leached from the plant material by irrigation and was detected in the soil (1.9–3.4 µg kg⁻¹) and in the percolate (12–295 µg L⁻¹). In the case of ZEN, 27–50% of the mycotoxin leached from the residual maize stubbles due to watering but was only occasionally detected in traces in the soil and not found in the percolate. The results clearly reveal a leaching potential of both DON and ZEN, respectively, but a mobilisation with water was only observed for DON. Temperature confirmed to be a key factor, affecting the fate of the mycotoxins in the soil by driving the interaction between different soil fauna members as well as functional and trophic levels within the soil food web.

Agricultural trichothecene mycotoxin contamination affects the life-history and reduced glutathione content of Folsomia candida Willem (Collembola)

There is limited data available concerning the effect of T-2/HT-2 toxin or deoxynivalenol (DON) on invertebrates such as springtails, and no data on their life history and oxidative stress. Control maize and DON or T-2 toxin contaminated maize were fed to Folsomia candida with a toxin content of 16324 mg DON kg–1 or 671 mg T-2 kg–1 maize. Ten to twelve days old animals were investigated in a life-history test and a stress protein test.T-2 toxin did not affect Folsomia candida in any measured parameters. The DON exposed group showed decreased growth and reproduction, and a higher survival rate. DON treatment resulted in lower protein content, while reduced glutathione content was higher than in control. It suggests that DON activated the glutathione-related detoxification pathway, which possibly causes a higher survival rate. The results also suggest that the oral toxicity of DON or T-2 is lower than through physical contact.For that reason, DON and T-2 toxin contaminated maize is not suggested to be used as green manure in the native state. Alternative solutions could be using mycotoxin contaminated maize for biogas production, or after decontamination by bacterial strains, it can be used as organic fertilizer.