Influence of Soil Organic Matter and Soil Surfaces on a Bacterial Consortium that Mineralizes Fenamiphos

Microorganisms are often responsible for enhanced degradation of pesticides in soil. This study was conducted to isolate microorganisms capable of mineralizing fenamiphos [ethyl-3-methyl-4-(methylthio)-phenyl(1-methylethyl)phosphoramidate] from soil collected at a turfgrass site that showed an enhanced degradation rate of the chemical. Batch-culture enrichment techniques were employed to isolate microorganisms from the soil capable of mineralizing C-14-fenamiphos, and the evolved (CO2)-C-14 was quantified by liquid scintillation counting. No axenic bacterial cultures capable of mineralizing fenamiphos could be isolated. A mixed bacterial consortium enriched with glucose-basal mineral medium mineralized fenamiphos only in the presence of a small amount of the nonsterile soil, autoclaved soil, or H2O2-treated soil. The mixed culture consisted of at least 6 gram-negative rod-shaped bacteria, with none of the individual isolates having any capacity to mineralize fenamiphos. The mixed culture grew well in soil extract and, at the same time, mineralized fenamiphos. This suggests that soluble organic components serve as inducers for the production of enzymes necessary for the mineralization of fenamiphos or that soil surfaces might play a role in induction of the enzymes.