Biodegradation of nylon oligomers
This mini-review is a compendium of the degradation of a man-made compound, 6-aminohexanoate-oligomer, in Flavobacterium strains. The results are summarized as follows:
1. Three enzymes, 6-aminohexanoate-cyclic-dimer hydrolase (EI), 6-aminohexanoate-dimer hydrolase (EII), and endotype 6-aminohexanoate-oligomer hydrolase (EIII) were responsible for degradation of the oligomers.
2. The genes coding these enzymes were located on pOAD2, one of three plasmids harbored in Flavobacterium sp. KI72, which comprised 45,519 bp.
3. The gene coding the EII′ protein (a protein having 88% homology with EII) and five IS6100 elements were identified on pOAD2.
4. The specific activity of EII was 200-fold higher than that of EII′. However, altering two amino acid residues in the EII′ enzyme enhanced the activity of EII′ to the same level as that of the EII enzyme.
5. The deduced amino acid sequences from eight regions of pOAD2 had significant similarity with the sequences of gene products such as oppA-F (encoding oligopeptide permease), ftsX (filamentation temperature sensitivity), penDE (isopenicillin N-acyltransferase) and rep (plasmid replication).
6. The EI and EII genes of Pseudomonas sp. NK87 (another nylon oligomer-degrading bacterium) were also located on plasmids.
7. Through selective cultivation using nylon oligomers as a sole source of carbon and nitrogen, two strains which initially had no metabolic activity for nylon oligomers, Flavobacterium sp. KI725 and Pseudomonas aeruginosa PAO1, were given the ability to degrade xenobiotic compounds. A molecular basis for the adaptation of microorganisms toward xenobiotic compounds was described.