SULFONAMIDE INHIBITION IN MONOCHRYSIS LUTHERP(1)

The effect of sulfonamides on growth of the chry-somonad, Monochrysis lutheri, in a synthetic sea-water medium was examined over a period of 14 days. The population increased at all sulfonamide concentrations during the first several days of incubation before inhibition became apparent. Inhibitory concentrations ranged from 0.01 to 1.0 mg%. Inhibition luas most pronounced in sulfathiazole; sulfamethazine, sulfapyridine, and sulfanilamide followed in decreasing order. p-Arninobenzoic acid (0.001-1.0 mg%) competitively reversed inhibition. Folic acid, thymine, adenine, and vitamin B12 neither reversed the inhibition nor spared the requirement for p-aminobenzoic acid. The significance of the inhibition pattern and the potential use of antimetabolites in the marine environment were discussed.