Abstract
Flavobacterium sp. strain KI725 harbors plasmid pOAD21, a derivative of nylon oligomer-degradative plasmid pOAD2, in which all of nylA (the gene for 6-aminohexanoate cyclic dimer hydrolase [EI]) was deleted but nylB (the gene for 6-aminohexanoate dimer hydrolase [EII]) was retained. KI725 showed no growth on unfractionated nylon oligomers (Nom1) obtained from a nylon factory as a sole carbon and nitrogen source (Nom1 minimum plate). Extracts of KI725 cells possessed hydrolytic activity for Nom1 (approximately 5% of the activity of KI72), but pOAD2-cured strains (KI722 and KI723) showed no activity. KI725R strains which grew on the Nom1 minimum plate were spontaneously isolated from KI725 at a frequency of 10(-7) per cell. Activity toward Nom1 was enhanced in KI725R strains (10 to 30% of the activity of KI72). This new Nom1 degrading enzyme (EIII, the nylC gene product) hydrolyzed not only Nom1 but also the N-carbobenzoxy-6-aminohexanoate trimer, a substrate which was not hydrolyzed by either EI or EII. Cloning and sequence analysis showed that the nylC gene is located close to nylB on pOAD21 and is a 1,065-bp open reading frame corresponding to 355 amino acid residues. The nucleotide sequence of the nylC gene and the deduced amino acid sequence of EIII had no detectable homology with the sequences of nylA (EI) and nylB (EII).