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Reasons for the Acclimation for 2,4-D Biodegradation in Lake Water

Dep. of Agronomy, Cornell Univ., Ithaca, NY 14853.

ABSTRACT

A study was undertaken to determine reasons for the occurrence of an acclimation period for the biodegradation of 2,4-dichlorophenoxyacetate (2,4-D) in lake water. The length of the acclimation period was not affected by removal of larger protozoa from the water or the presence of cycloheximide and nystatin. The population of 2,4-D-degrading bacteria increased long before 2,4-D loss was detected, and herbicide loss was evident only when the population size was large. The acclimation phase was virtually eliminated if a culture of 2,4-D-utilizing bacteria was added to lake water. A culture of glucose-grown 2,4-D-degrading bacteria metabolized the herbicide in a time interval far shorter than the acclimation phase. The time for acclimation was identical in 14 replicate samples of the same lake water. These data suggest that the length of the acclimation phase is not mainly a result of the time for reduction of grazing pressure on 2,4-D-degrading bacteria, the destruction of antimicrobial compounds, the decomposition of alternative C sources used preferentially to the herbicide, induction of the requisite enzymes, or the appearance of a mutant able to utilize the pesticide. The acclimation for 2,4-D degradation in lake water appears chiefly to reflect the time for a small population of bacteria able to use the compound to become sufficiently large to cause a detectable loss of the chemical.

Present address of senior author is Dep. of Plant and Soil Science, Montana State Univ., Bozeman, MT. 59717. *Corresponding author.

Received for publication June 22, 1988.