Abstract: A cypermethrin-degrading strain named B-1 was isolated from soil samples collected from a tea garden in Ya’an, Sichuan province. According to its morphological, physiological and biochemical characteristics and 16S rDNA sequence (GenBank Accession No. HQ009796 ), B-1 was identified as Bacillus licheniformis. B-1 degraded cypermethrin by a co-metabolic mechanism and the degradation rate was 93.93% for 20 mg/L cypermethrin in 72 h and 70.35% for 100 mg/L cypermethrin in 240 h. 3-PBA was detected as an intermediate product during the degradation process. The degradation rates for deltamethrin, cyfluthrin and fenvalerate at a concentration of 20 mg/L were 95.62%, 79.73% and 55.67% in 72 h, respectively. B-1 could produce a non-inducible esterase that degrades cypermethrin. The enzyme was found both inside and outside the cells mainly as an extracellular product. Isozyme electrophoresis analysis suggested that intracellular and extracellular esterase extracts from strain B-1 had the same esterase electrophoretic pattern. Acute toxicity tests showed that culture supernatant of strain B-1 had no observed toxicity for mice.

Key words: cypermethrin, biodegradation, Bacillus licheniformis, degradation characteristics