Acute Toxicity of Cresols to Pseudomonas — An Initial Oxygen Uptake Method

Acute toxicity of cresols to both Pseudomonas I and II was estimated by an initial oxygen uptake method. Inhibition studies of toluene and cresols on the oxidation of either benzoate by Pseudomnas I or phenol by Pseudomonas II were analyzed and expressed as oxygen uptake rates. Double reciprocal plots for the inhibiton by cresols of oxygen uptake in Pseudomonas , two physical constants, Vmaxi and Ki, were obtained. The Vmaxi of o −, m − and p ‐cresol were 80%, 81% and 57% of Vmax in Pseudomnas I, and 10%, 25% and 36% in Pseudomonas II, respectively. Thus, the toxicity to Pseudomonas I decreases in the order p ‐ > o ‐ ≥ m ‐cresol, whereas to Pseudomonas II, the order is changed to o ‐ > m ‐ > p ‐cresol. This difference in the toxicity order is probably due to the allosteric effect of p ‐cresol towards Pseudomonas II. Inasmuch as most compounds inhibit noncompetively, the relative toxicity of different compounds can be estimated by a new toxicity parameter RI (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 ≥ m ‐cresol > o ‐chlorophenol > toluene > phenol.