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The marine ciliateParauronema acutum converted 2-aminofluorene and 2-acetylaminofluorene to compounds with mutagenic activity in the AmesSalmonella test. The ciliate, however, did not activate benzo (α)pyrene or benzanthracene or destroy the mutagenic properties of nitrosoguanidine. Homogenates, when substituted for the liver S-9 fraction in theSalmonella /microsome test, activated 2-aminofluorene and 2-acetylaminofluorene to mutagens. Benzo(α)pyrene and benzanthracene were not activated, nor was nitrosoguanidine inactivated. Phenobarbitol did not induce or increase the amount of activating activity. The activation showed no requirement for the reduced nicotinamide adenine dinucleotide phosphate-regenerating system required by liver P-450 cytochromes. Upon differential sedimentation of a cell homogenate, the majority of the activity sedimented with a small-particle fraction with sedimentation properties like those of microsomes from higher eucaryotes. Benzo(α)pyrene, although not metabolized, was accumulated by cultures ofP. acutum at a linear rate and was not appreciably released (10%) after removal of benzo(α)pyrene from the incubation medium. Hence, this ciliate could convert certain polynuclear aromatic hydrocarbons to mutagens and accumulate others.

Activation of Polynuclear Aromatic Hydrocarbons to Mutagens by the Marine Ciliate Parauronema acutum