Indicator media for microorganisms degrading chlorinated pesticides

A bromocresol purple liquid indicator medium and an eosin-methylene blue agar have been developed for the demonstration and isolation of microorganisms able to degrade the chlorinated herbicide, 2,4-dichlorophenoxyacetic acid (2,4-D). Plates of the eosin-methylene blue agar indicate individual 2,4-D-degrading bacterial colonies. Both indicator systems show the production of acid, presumably hydrochloric, during degradation of the 2,4-D in the media. Concentrations of 2,4-D required to give an acid reaction in media with varying concentrations of yeast extract were determined; the production of about 0.24 mmol of hydrochloric acid seems necessary to counteract the buffering effect of 100 mg of metabolized yeast extract. Acid production from the herbicide, 4-chloro-2-methylphenoxyacetic acid(MCPA), which in the salt form could yield only small amounts of hydrochloric acid, was inconsistent. The two indicator media should be useful in investigations of the microbial degradation of other acid-yielding halogenated pesticides.