Studies on the Production of Pink Pigment in Pseudomonas extorquens NClB 9399 Growing in Continuous Culture

S ummary . The pink pigment of Pseudomonas extorquens was identified tentatively as an oxo‐carotenoid similar to rhodoxanthin. The production of the pigment increased at the end of the logarithmic phase of growth of Ps. extorquens in batch cultures. It was produced during growth on a wide variety of carbon and nitrogen sources, with the exception of ethanol, but not in the presence of diphenylamine, an observation which was consistent with the identification of the pigment as a carotenoid. The organism was grown in continuous culture under conditions of oxygen and magnesium limitation which might be expected to restrict the oxidation of γ‐carotenes to pink pigments. However, such limitations caused an increase in pigmentation over that of methanol‐limited cultures. Non‐pink mutants of Ps. extorquens , obtained after the use of the mutagen, ethyl methyl sulphonate, did not have growth‐rates lower than those of the parent strain. The pigment would seem to have no central metabolic role in actively growing cells but carbon is diverted to pigment production when growth is restricted by other than carbon limitation.