Detoxication of Hormone Herbicides by Soil Bacteria

Abstract

THE selective herbicides 2,4-dichlorophenoxyacetic acid (DCPA) and 2-methyl-4-chlorophenoxyacetic acid (MCPA) are known to undergo a gradual detoxication in soil due to biological agencies, and Audus^1,2 has recently reported the isolation of a bacterium capable of decomposing the former, which is apparently utilized as a source of carbon. In the course of work on herbicide detoxication in soil, we have succeeded in isolating two types of bacteria with similar properties from soil repeatedly treated with 2,4-dichlorophenoxyacetic acid. Pure cultures were readily obtained by plating from soil on an agar medium containing 0.10 per cent sodium salt of the acid as the sole source of carbon. The first organism (No. 1) grew abundantly in ordinary bacteriological media and was identified as Flavobacterium aquatile (Bergey³). The second (No. 2) bore some morphological resemblance to the organism studied by Audus—small, irregular, non-spore-forming, non-motile rods of a Corynebacterium-like appearance, but Gram-negative, sometimes with Gram-positive granules. It grew very feebly in ordinary media and showed no conspicuous biochemical activities; but on ammonium phosphate agar with 0.1–0.2 per cent sodium salt of 2,4-dichlorophenoxyacetic acid or 2-methyl-4-chlorophenoxyacetic acid it produced a slow but eventually quite vigorous, whitish and slimy growth. A mere trace of growth occurred on the basal medium without added organic matter. Glucose and glycerol were utilized very poorly; phenol, sodium benzoate and sodium salicylate not at all.