Degradation of glyphosate using environmental lignocellulolytic fungal isolates and extracellular enzymes

MSc (Microbiology), North-West University, Potchefstroom Campus

Glyphosate is the most used herbicide in the world. Having been detected in food and water systems, glyphosate raises several concerns around food safety and its environmental impact. Recent studies have found an increase in environmental levels of glyphosate in agricultural soils as well as in food. Glyphosate is reported to be likely carcinogenic and potentially poses a great risk to human health. In this study, environmental fungal isolates capable of degrading glyphosate were chosen from a previous study, along with environmentally acquired fungal isolates. The study aimed to evaluate these fungal isolates as well as their extracellular enzymes for the degradation of glyphosate in vitro. Fungal species were isolated from soil samples (0.5 g) and sub-cultured until pure cultures were obtained. Isolates were grown in a liquid media consisting of brewery spent grain (BSG), yeast nitrogen base (YNB) and distilled water. The extracellular fluid was used to test the degradation of Roundup through thin-layer chromatography plates (TLC plates). Isolates capable of glyphosate degradation were sequenced and identified, tested in spiked microcosms and analysed using enzyme-linked immunosorbent assay (ELISA). The results showed Penicillium adametzioides to be the most promising isolate through screening tests (52.06% ± 3.96% degraded). Trichoderma virens showed the largest level of degradation in soil with 22.03% ± 6.88% glyphosate remaining after 10 days. Nutrient analysis of soil was used as an indication of potential degradation pathways the isolates could follow to build on ELISA and TLC tests. According to the pure Roundup degradation test Cladosporium cladosporioides (3.69% ± 1.07% glyphosate remaining) and Aspergillus niger (4.15% ± 0.18% glyphosate remaining) showed the best results in using Roundup as a sole source of nutrients. In conclusion, the fungal isolates in this study can potentially degrade glyphosate in soil, and some even use Roundup as the nutrient source. In future studies, the viability of these isolates should be tested in soil conditions and also against a range of different pesticides.

Masters