INFLUENCE OF SOIL ORGANIC-MATTER AND SOIL SURFACES ON A BACTERIAL CONSORTIUM THAT MINERALIZES FENAMIPHOS

Microorganisms are often responsible for enhanced degradation of pesti cides in soil. This study was conducted to isolate microorganisms capa ble of mineralizing fenamiphos (methylthio)-phenyl(1-methylethyl)phosp horamidate] from soil collected at a turfgrass site that showed an enh anced degradation rate of the chemical. Batch-culture enrichment techn iques were employed to isolate microorganisms from the soil capable of mineralizing C-14-fenamiphos, and the evolved (CO2)-C-14 was quantifi ed by liquid scintillation counting. No axenic bacterial cultures capa ble of mineralizing fenamiphos could be isolated. A mixed bacterial co nsortium enriched with glucose-basal mineral medium mineralized fenami phos only in the presence of a small amount of the nonsterile soil, au toclaved soil, or H2O2-treated soil. The mixed culture consisted of at least 6 gram-negative rod-shaped bacteria, with none of the individua l isolates having any capacity to mineralize fenamiphos. The mixed cul ture grew well in soil extract and, at the same time, mineralized fena miphos. This suggests that soluble organic components serve as inducer s for the production of enzymes necessary for the mineralization of fe namiphos or that soil surfaces might play a role in induction of the e nzymes.