Biodegradation of Glyphosate by Fungi Species

F.E. Adelowo, O.A. Olu-Arotiowa, O.S. Amuda

Abstract


Pesticides are chemicals that combat the attack of various pests on agricultural crops. The use of synthetic pesticides has become an indispensable tool in agriculture. Their use over the years has led to serious environmental pollution. In view of this, efforts have been made by scientists to remove these pollutants from the environment. Degradation of pesticides pollutants by the use of microorganisms has been one of the most environmentally safe and cost effective methods, since these microorganisms exist in abundance in the environment. Glyphosate, an herbicide used for the control of weeds was made to undergo degradation by fungi isolates. The fungi growth was monitored by measuring cell turbidity with a UV-visible spectrophotometer (Genesys IOS VI) at 660nm. The released phosphate ion was determined by spectrophotometric analysis using a UV-Visible spectrophotometer (Genesys IOS VI) at 690nm, using Trichoderma viridae, Aspergillus niger, and Fusarium  oxysporum fungi as biodegraders. The release of phosphate ion, was an indication that the first step in glyphosate degradation by fungi is cleavage of the Carbon-Phosphorus bond, resulting in the release of an inorganic phosphate which could be utilized as a source of phosphorus by fungi. There was an inverse relationship between the fungus growth and the amount of phosphate ion in the broth culture over a period of time. The products of degradation were determined by Thin-Layer Chromatography (TLC) and High Performance Liquid Chromatography(HPLC). Three spots were detected in Thin Layer Chromatographic analysis while three peaks were detected in High Performance Liquid Chromatographic analysis. The spots and peaks were identified as glyphosate, aminomethyl phosphonic acid (AMPA) and sarcosine respectively. The results showed that the isolated fungi species were able to utilize glyphosate as both Phosphorus and Nitrogen sources for their growth. These could only be possible through breaking of C-P and C-N bonds. The percentage concentration of detectable sarcosine present in the culture broth was far greater than that of AMPA(sarcosine, 89% and AMPA, 6%), when analysed by HPLC. This suggested that the major metabolic degradation pathway of glyphosate is through the breaking of Carbon-Phosphorus (C-P) bond.  The percentage of residual glyphosate present by the 7th day was about 5%.

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