SOME MORPHOLOGICAL AND BIOCHEMICAL CHARACTERISTICS OF A SOIL BACTERIUM WHICH DECOMPOSES 2,4-DICHLOROPHENOXYACETIC ACID

Abstract

A new Achromobacter species which decomposed 2,4-dichlorophenoxyacetic acid (2,4-D), apparently to small molecules, was isolated from a soil treated with successive closes of the herbicide. The organism grew poorly or not at all on common laboratory media in the presence or absence of 2,4-D. Investigation of its carbon, nitrogen, mineral, and vitamin requirements in agar containing 2,4-D showed that the best growth stimulants were the dicarboxylic acids of the tricarboxylic acid cycle, bicarbonate, formate, urea, and L-histidine. Calcium or magnesium and probably iron were required for maximum growth. Some aryloxy acids, phenolic compounds, and an ester were tested for their ability to replace 2,4-D as growth substrate or to inhibit growth in the presence of 2, 4-D, and it was found that the ethyl ester of 2,4-D and chlorophenolic substances were most toxic. Only 2-methyl-4-chlorophenoxyacetic acid (MCPA) and less readily, 4-chlorophenoxyacetic acid, phenoxyacetic acid, and resorcinol could substitute for 2,4-D. Good cell multiplication and herbicide decomposition were obtained in an aerated mineral salts medium containing 2,4-D, yeast extract, and 0.005 ML-malic acid. Maximum growth (ca. 109cells/ml.) occurred in 4 to 5 days and 2,4-D decomposition was essentially complete in 6 to 7 days. Resting cells were able to oxidize 2,4-D, MCPA, 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), and 2,4-dichlorophenol (2,4-DCP) and to release 94% of the 2,4-D chlorine as chloride. High concentrations of yeast extract caused growing cells to accumulate 2,4-DCP.