A technique derived from the tritiated thymidine method was used to characterize the effects of synthetic organic compounds (SOCs) on the specific rate of bacterial death as functions of chemical concentration, the physiological state of the cells, and exposure time to the toxicant. The rate of bacterial death was estimated by following over time the release of radioactive tracer from the DNA of thymidine-requiring (thy) mutant E. coli cells (ATCC 23820). Results indicate that the lysis rate of unexposed microbial cultures was the same whether or not the cells were growing or had reached the stationary phase. Lysis rates were calculated from exposures to single SOCs: acrylonitrile, ethylene glycol, isophorone, phenol, 2-chloro- and 4-chlorophenol. The concentrations tested were 250, 1000 and 5000 mg COD/l. The major effect observed with stationary-phase cultures was a stimulation of the rate of lysis, whereas a reduction in the rate of lysis was the primary effect observed with growing cells. A physiological interpretation for these opposite effects is provided. The physiological state of the microorganisms influenced the magnitude, intensity and type of effects caused by the presence of synthetic organic compounds.

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