ACUTE TOXICITY OF CRESOLS TO PSEUDOMONAS - AN INITIAL OXYGEN-UPTAKE METHOD

Acute toxicity of cresols to both Pseudomonas I and II was estimated b y an initial oxygen uptake method. Inhibition studies of toluene and c resols on the oxidation of either benzoate by Pseudomnas I or phenol b y Pseudomonas II were analyzed and expressed as oxygen uptake rates. D ouble reciprocal plots for the inhibiton by cresols of oxygen uptake i n Pseudomonas, two physical constants, Vmaxi and Ki, were obtained. Th e Vmaxi of o-, m- and p-cresol were 80%, 81% and 57% of Vmax in Pseudo mnas I, and 10%, 25% and 36% in Pseudomonas II, respectively. Thus, th e toxicity to Pseudomonas I decreases in the order p- > o- greater tha n or equal to m-cresol, whereas to Pseudomonas II, the order is change d to o- > m- > p-cresol. This difference in the toxicity order is prob ably due to the allosteric effect of p-cresol towards Pseudomonas II. Inasmuch as most compounds inhibit noncompetively, the relative toxici ty of different compounds can be estimated by a new toxicity parameter RT (relative inhibition) which is defined as 100/Ki. By comparing the RI value of each compound, the toxicity to Pseudomonas I decreases in the order m-chlorophenol > p-cresol > p-chlorophenol > o-cresol great er than or equal to m-cresol > o-chlorophenol > toluene > phenol.