Non-specific biodegradation of the organophosphorus pesticides, cadusafos and ethoprophos, by two bacterial isolates

An enrichment culture technique was used for the isolation of microorganisms responsible for the enhanced biodegradation of the nematicide cadusafos in soils from a potato monoculture area in Northern Greece. Mineral salts medium supplemented with nitrogen (MSMN), where cadusafos (10 mg l ^-1) was the sole carbon source, and soil extract medium (SEM) were used for the isolation of cadusafos-degrading bacteria. Two pure bacterial cultures, named CadI and CadII, were isolated and subsequently characterized by sequencing of 16S rRNA genes. Isolate CadI showed 97.4% similarity to the 16S rRNA gene of a Flavobacterium strain, unlike CadII which showed 99.7% similarity to the 16S rRNA gene of a Sphingomonas paucimobilis. Both isolates rapidly metabolized cadusafos in MSMN and SEM within 48 h with concurrent population growth. This is the first report for the isolation and characterization of soil bacteria with the ability to degrade rapidly cadusafos and use it as a carbon source. Degradation of cadusafos by both isolates was accelerated when MSMN was supplemented with glucose. In contrast, addition of succinate in MSMN marginally reduced the degradation of cadusafos. Both isolates were also able to degrade completely ethoprophos, a nematicide chemical analog of cadusafos, but did not degrade the other organophosphorus nematicides tested such as isazofos and isofenphos. Inoculation of a soil freshly treated with cadusafos or ethoprophos (10 mg l^-1) with high inoculum densities (4.3 × 10⁸ cells g^-1) of Sphingomonas paucimobilis resulted in the rapid degradation of both nematicides. These results indicate the potential of this bacterium to be used in the clean-up of contaminated pesticide waste in the environment.