Proposed pathway of 4-aminopyridine degradation by the enrichment culture. I, 4-aminopyridine; II, 3,4-dihydroxypyridine; III, 3-(N-formyl)-formiminopyruvate; and IV, 4-amino-3-hydroxypyridine. The ring-cleavage product 3-(N-formyl)-formiminopyruvate from 3,4-dihydroxypyridine was hypothesized from the metabolic pathway of 3,4-dihydroxypyridine in Agrobacterium sp. NCIB 10413 [6, 7]. The strains of the enrichment culture probably involved in the steps are indicated.