Metabolism of Some Organophosphorus Insecticides by Microorganisms1

Abstract

The metabolism by some soil microorganisms of Thimet, Am. Cyanamid 12008, their oxidation products and certain other organophosphates was investigated. The yeast, Torulopsis utilis , the bacteria, Pseudomonas fluorescens and Thiobacillus thiooxidans , and the green alga, Chlorella pyrenoidosa were grown in pure cultures under aseptic conditions. The first two organisms were grown in a glucose-yeast extract medium and the latter two in mineral solutions. Rate studies were made on the hydrolysis and oxidation of organophosphates introduced into the cultures as emulsions at 1,000 p.p.m. Torulopsis and Chlorella reacted similarly with the thiophosphates. It appeared as if the organophosphates were rapidly absorbed by the organisms, and then slowly released from the living and dead cells in the cultures. With both organisms the S-(alkylthio) methyl derivatives were much more rapidly hydrolyzed than the S-(alkylsulfonyl)methyl, and the latter only slightly faster than the S-(alkylsulfinyl)methyl compounds. In all cases the phosphorodithioate sulfoxides were the most stable and the phosphorothiolate sulfides were the least stable derivatives in the presence of the organisms. With Chlorella , Thimet was oxidized to the phosphorodithioate sulfoxide, which was very stable to hydrolysis but slowly converted to the phosphorothiolate sulfoxide with little if any phosphorothiolate sulfide or sulfones being formed. Both Torulopsis and Chlorella oxidized the sulfides to sulfoxides, but Chlorella was more effective in oxidizing the phosphorodithioates to phosphorothiolates. Little if any oxidation was found with parathion, Dow ET-57, dimefox and schradan in Chlorella cultures. The two bacteria failed to oxidize Thimet but were effective at hydrolyzing this compound. Thiobacillus could not utilize sulfur from the Thimet molecule.