Abstract
Without pretreatment of Ushiku loam upland soil with the organophosphorus insecticide salithion (2-methoxy-4H-1, 3, 2-benzodioxaphosphorin-2-sulfide), the ratios of salithion-degrading bacteria, actinomycetes and fungi to the corresponding total microorganisms in the soil were 14, 44 and 16%, respectively. Among them, Acinetobacter sp. (B-60) degraded 82% of applied 10-ppm salithion in culture during 8hr of incubation. The high degrading activity of this strain was probably due to its high salithion-demethylating activity. Agrobacterium sp. (B-7, B-15 and B-17) degraded 51-62% of applied salithion during 48hr. This high degrading activity of the strains was probably due to their high activity in cleaving the P-O-aryl bond of salithion than the other microorganisms. The degrading activity of isolated actinomycetes and fungi was not as high as that of the bacterial strains. None of the isolated microorganisms grew with salithion as a sole carbon source, while some strains used salithion as a sole phosphorus source. Demethylation and cleavage of P-O-aryl and P-O-aralkyl linkages of salithion were the first metabolic processes by the isolated soil microorganisms.
