Toxin Resistance in Aquatic Fungi Poses Environmentally Friendly Remediation Possibilities: A Study on the Growth Responses and Biosorption Potential of Mucor hiemalis EH5 against Cyanobacterial Toxins

Cyanobacteria produce various harmful secondary metabolites, which pose a serious global threat to aquatic ecosystems and human health. Biodegradation is an important topic of water purification research and offers especially an environmentally friendly remediation strategy. Here, we present a water fungus of the genus Mucor that shows considerable promise to be applied as a mycoremediation agent for the removal of cyanobacterial toxins from aquatic environments. In the present study, we investigated the effect of three different cyanobacterial toxins, namely the hepatotoxin microcystin-LR, the neurotoxin β-N-methylamino-l-alanine and the cytotoxin cylindrospermopsin, on the sensitivity of Mucor hiemalis EH5 using an adaptation of the Kirby-Bauer disk diffusion assay, and the influence of the toxins on fungal growth and biomass production via radial extension and dry weight (DW) measurements. Additionally, we established an optimized strategy for the individual cyanobacterial toxin extraction from the vegetative part of Mucor hiemalis EH5 and analyzed its biosorption potential via LC-MS/MS measurements. The fungal microorganism showed a fast adaptation behavior and strong resistance towards the toxins. No significant differences in terms of growth were perceived when comparing the exposed fungi to an untreated control. This indicates that the cyanobacterial toxins are not lethal to the fungus and that the organism can grow and develop undisturbed in their presence. Toxin uptake was quantified by LC‑MS/MS detection with recoveries for the established extraction methods of >60-85%. After exposing the fungi to each of the toxins respectively for 24 and 48 hours, we found a significant uptake (p<0.05) in the range of 0.1 to 1.7 mg of the applied toxin per gram mycelial biomass (dw). Our results suggest that Mucor hiemalis EH5 is an ideal organism to be tested in further studies as a biodegrading system for the remediation of cyanobacterial toxins from contaminated waters.