Bacterial uptake of octyl ethanolamine increases with pH

The uptake of octyl ethanolamine (C8EA) by Pseudomonas pseudoalcaligenes was determined at pH 7.1-10.0. At pH 9.1 the total uptake was nearly three times higher and at pH 10.0 four times higher than at pH 7.1. Also the initial rate of uptake was lowest at pH 7.1. At pH 7.1 five to ten times higher concentrations of C8EA were needed than at pH 9.1 to achieve the same degree of leakage of cytoplasmic constituents. The results support the hypothesis that penetration of the bacterial cytoplasmic membrane by C8EA in its uncharged form is favoured. This takes place particularly with high pH in the suspending medium. In the cytoplasm, the pH is lower, and C8EA becomes more protonated. This will prevent back diffusion, promote accumulation and enhance membrane interaction and toxicity at high pH.