Biodegradation of imidacloprid in liquid media by an isolated wastewater fungus Aspergillus terreus YESM3

ABSTRACT

In the present study, a new fungal strain capable of imidacloprid degradation was isolated from agricultural wastewater drain. The fungal strain of YESM3 was identified as Aspergillus terreus based on ITS1-5.8S rDNA-ITS2 gene sequence by PCR amplification of a 500 bp sequence. Screening of A. terreus YESM3 to the insecticide imidacloprid tolerance was achieved by growing fungus in Czapek Dox agar for 6 days at 28°C. High values (1.13 and 0.94 cm cm⁻¹) of tolerance index (TI) were recorded at 25 and 50 mg L⁻¹ of imidacloprid, respectively in the presence and absence of sucrose. However, at 400 mg L⁻¹ the fungus did not grow. Effects of the imidacloprid concentration, pH, and inoculum size on the biodegradation percentage were tested using Box–Behnken statistical design and the biodegradation was monitored by HPLC analysis at different time intervals. Box–Behnken results indicated that optimal conditions for biodegradation were at pH 4 and two fungal discs (10 mm diameter) in the presence of 61.2 mg L⁻¹ of imidacloprid. A. terreus YESM3 strain was capable of degrading 85% of imidacloprid 25 mg L⁻¹ in Czapek Dox broth medium at pH 4 and 28°C for 6 days under static conditions. In addition, after 20 days of inoculation, biodegradation recorded 96.23% of 25 mg L⁻¹ imidacloprid. Degradation kinetics showed that the imidacloprid followed the first order kinetics with half-life (t₅₀) of 1.532 day. Intermediate product identified as 6-chloronicotinic acid (6CNA) as one of the major metabolites during degradation of imidacloprid by using HPLC. Thus, A. terreus YESM3 showed a potential to reduce pollution by pesticides and toxicity in the effected environment. However, further studies should be conducted to understand the biodegradation mechanism of this pesticide in liquid media.

KEYWORDS:

• Biodegradation
• imidacloprid
• box–behnken
• A. terreus
• HPLC
• 6-chloronicotinic acid