A new optically active phenolic alkaloid with the composition C10H11NO2S, mp 85-88°C, [α]D +28° (c 1.0; chloroform) (I) has been isolated from the microorganism Pseudomonas aeruginosa (strain 590) and has been called aerugine. The action of diazomethane gave an O-methyl derivative (II). On the basis of the formation of ortho-cresol by the hydrogenolytic desulfuration reaction, a study of the IR, mass, and PMR spectra and (I) and its acetyl derivative (III), and also the13C NMR spectrum of (I), the structure of 4-hydroxymethyl-2-(o-hydroxyphenyl)-2-thiazoline has been established for aerugine. The spectral characteristics of the compounds mentioned are given. © 1988 Plenum Publishing Corporation.