Biodegradation of the organophosphorus insecticide fenitrothion by the alga Chlamydomonas reinhardtii: The role of cytochrome P450 monooxygenase.

Abstract

Cultures of Chlamydomonas reinhardtii (1 $\times$ 10$\sp6$ cells/mL) were incubated with 5.0 $\mu$g/mL of the insecticide fenitrothion, (FEN), (O,O-dimethyl-O-(3-methyl-4-nitrophenyl)phosphorothioate). The rate of abiotic fenitrothion degradation in Gorman and Levign growth medium (pH = 6.8, T = 21 $\sp\circ$C, Vita Lite$\sp\circler$ 40 w/m$\sp2$), was enhanced 9-fold in the light relative to the dark under abiotic conditions (T$\sb{1/2}$ values of 145 h (light) and 54 days (dark)). Endogenous metabolism by C. reinhardtii produced significant amounts of 3-methyl-4-nitrophenol (nitrocresol), demethyl fenitrothion, formyl fenitrothion, hydroxymethyl fenitrothion, and carboxyfenitrothion within the cells. This biodegradation was slower in the dark than in the light. Studies of algal biodegradation of fenitrothion in the presence of 5.0 $\mu$g/mL fenitrothion plus 23.2 $\mu$g/mL phenobarbital, (a cytochrome P$\sb{450}$ monooxygenase inducer), demonstrated a 10 fold increase in the levels of intracellular hydroxymethyl fenitrothion relative to control algal cultures. It was concluded from this study that degradation of fenitrothion by metabolic activity of cytochrome P$\sb{450}$ monooxygenase may be a significant determinant in fenitrothion degradation in C. reinhardtii cultures. The amounts of formyl fenitrothion, carboxy fenitrothion and, carboxyfenitrooxon were demonstrated to depend on the availability of intracellular hydroxymethyl fenitrothion pool produced by algal PSMO activity, while NC and DSM levels were attributable to other cellular enzymes. (Abstract shortened by UMI).