Microcystins produced by harmful cyanobacterial blooms in eutrophic freshwater resources is an expanding global problem, threatening both the ecosystem and mankind. Biodegradation using indigenous microbes from lakes with a history of cyanobacterial blooms is considered an efficient method for removal of microcystins (MCs) from freshwater resources like lakes. Although some species of bacteria have been shown to degrade microcystins, very little has been done to look into the role of fungi for biodegradation. Recent studies have examined the ability of white rot fungus as an algicidal but their ability to degrade MCs haven’t been studied yet. Fungal isolates capable of degrading MC and MC- producing algae could prove beneficial for usage in the treatment of water in natural, lake-like environments. To obtain MC+ cultures, water and surface sediment samples were collected from Lake Erie in the summer of 2014 and 2015 during CyanoHABs. Colonies from the spread plates were picked and restreaked several times to obtain pure cultures. The obtained pure cultures were screened for MC+ (microcystin-degrading) isolates using MT2 BIO-LOG microplate-based assay supplemented with microcystin (1μg/ml) as the sole carbon source. The MC+ fungi detected was sequenced and identified based on staining procedures using lactophenol cotton blue and 18S rRNA gene sequencing. Fungal degradation rate was determined using ELISA for aliquots obtained from liquid media containing MC and fungal mycelium
Results/Conclusions
Of the 900 pure isolates obtained from sediment samples, one fungal isolate was confirmed as a microcystin degrader. The fungal isolate was shown to degrade microcystins in the concentration of 1µg/ml, within a span of 72 hrs. Its growth on PDA (Potato Dextrose Agar) was recognized as velvet like yellow to green mold appearance. Microscopy identified the fungi as having conidial heads which were short, columnar, and biseriate. The conidiophores were short, brownish and smooth-walled and conidia globose and rough-walled. The 18S rRNA sequencing for the isolate identified it taxonomically as Aspergillus nidulans. This indicates that similar to bacteria, fungal isolates belonging to Aspergillus spp. can degrade MCs too. Future work will test the algicidal capability of the fungus and its effects on toxin production in the natural lake environment.