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Isolation of Microorganisms from a Texas Soil Capable of Degrading Urea Derivative Herbicides¹

ABSTRACT

Samples of Hockley fine sandy loam were perfused with 500 µg/ml concentrations of monuron 3-(p-chlorophenyl)-1, 1-dimethylurea or diuron 3-(3,4-dichlorophenyl)-1, 1-dimethylurea for 2 weeks to isolate microorganisms tolerant to these concentrations. A fungus of the genus Fusarium and two unidentified bacteria were isolated by plating out small samples of the treated soil on Czapek's solution agar without sugar with 20 ppm of both herbicides added. The three isolates were tested for their ability to grow in solid and liquid media with different concentrations of the herbicides as sources of carbon. The same optimal growth of the fungus on Czapek's solution agar without sugar with 1 g/liter concentration of yeast extract was attained at 10 and 20 ppm monuron. When the yeast extract was excluded, best growth was attained at 2 ppm monuron. In Czapek's solution agar without sugar, and with 50 mg/liter of yeast extract, the fungus produced the highest amount of dry mycelia with 20 ppm monuron.

Cultures of the three isolates in Czapek's solution agar without sugar containing 20 ppm diuron, including 0.5 ppm of carbonyl ¹⁴C-diuron, were incubated for 2 weeks. The organisms grew profusely, but no breakdown products of diuron were detected from the extracts of these cultures as analyzed by TLC (thin layer chromatography) and strip scanning techniques. Approximately 3.5% of the added diuron was collected as ¹⁴CO₂ from soil samples incubated for 80 days with carbonyl labeled ¹⁴C-diuron and a mixture of the three isolates. Periodic analysis of soil samples from these experiments did not indicate any breakdown products of diuron apparently due to insensitivity of the instrumentation and procedures. However, data from the fungal growth and CO₂ evolution experiments suggest that these organisms can use monuron and diuron as a source of carbon.

¹ Contribution from the School of Agriculture, Prairie View A. and M. University, Prairie View, Texas 77445.

² Research Assistant and Professor of Soil Science, respectively, School of Agriculture, Prairie View A. and M. College, Prairie View, Texas 77445.

Received for publication June 4, 1973. Accepted for publication December 18, 1973.