A lycorine-degrading bacterium was isolated from the rhizosphere of Stmbergia lutea Ker Gawl plants. The organism, Pseudwnonas sp., strain ITM 3 11, was grown on a minimal medium with lycorine. Within 24-48 h, the alkaloid was transformed into three phenanthridinium derivatives (2, 3, and 4), two of which showed marked antibiotic activity. The evidence obtained demonstrates that the transformation consisted, essentially, in the oxidation of lycorine with an aromatization of the C ring and the conversion of the methylene group H2C(7)-N into an azomethyne group.