In 1975, a team of Japanese scientists discovered a strain of bacterium, living in ponds containingwaste water from anylon factory, that could digest certain byproducts ofnylon 6 manufacture, such as the linear dimer of6-aminohexanoate. These substances are not known to have existed before the invention ofnylon in 1935. It was initially named asAchromobacter guttatus.[4]
Studies in 1977 revealed that the threeenzymes that thebacteria were using to digest the byproducts were significantly different from any other enzymes produced by any other bacteria, and not effective on any material other than the manmade nylon byproducts.[5]
A few newer strains have been created by growing the original KI72 in different conditions, forcing it to adapt. These include KI722, KI723, KI723T1, KI725, KI725R, and many more.[8]
EII has evolved by gene duplication followed by base substitution of another protein EII'. Both enzymes have 345 identical aminoacids out of 392 aminoacids (88% homology). The enzymes are similar tobeta-lactamase.[12]
The EII' (NylB',P07062) protein is about 100x times less efficient compared to EII. A 2007 research by theSeiji Negoro team shows that just two amino-acid alterations to EII', i.e. G181D and H266N, raises its activity to 85% of EII.[9]
The structure of EIII was resolved in 2018. Instead of being a completely novel enzyme, it appears to be a member of the N-terminal nucleophile (N-tn) hydrolase family.[13] Specifically, computational approaches classify it as aMEROPS S58 (now renamed P1) hydrolase. The protein is expressed as a precursor, which then cleaves itself into two chains.[14][15] Outside of this plasmid, > 95% similar proteins are found inAgromyces andKocuria.[13] As of 2025, 9 homologues of NylC are described from different Actinobacteria (Plastic Enzyme Database PAZY., accessed 12.02.2025).[16]
EIII was originally thought to be completely novel.Susumu Ohno proposed that it had come about from the combination of agene-duplication event with aframeshift mutation. An insertion ofthymidine would turn an arginine-rich 427aa protein into this 392aa enzyme.[17]
There is scientific consensus that the capacity to synthesize nylonase most probably developed as a single-step mutation that survived because it improved the fitness of the bacteria possessing the mutation. More importantly, one of the enzymes involved was produced by aframe-shift mutation that completely scrambled transcribed amino acids.[18] Despite this, the new gene still had a novel, albeit weak, catalytic capacity. This is seen as a good example of how mutations easily can provide the raw material forevolution bynatural selection.[19][20][21][22]
A 1995 paper showed that scientists have also been able to induce another species of bacterium,Pseudomonas aeruginosa, to evolve the capability to break down the same nylon byproducts in a laboratory by forcing them to live in an environment with no other source of nutrients.[23]
Integration of EI and EII into the genome of the bacteriumPseudomonas putida KT2440 enabled the development of a strain that can metabolize Nylon oligomers.[24] Metabolism of common Nylon monomers likeaminocaproic acid andhexamethylenediamine was realised by the deregulation ofpolyamine metabolism, guided byAdaptive laboratory evolution experiments with nylon components as sole source of nutrients. Theadipic acid resulting from this metabolic pathway feeds into the central metabolism via a specializedbeta oxidation pathway obtained fromAcinetobacter baylyi.[25]
^Takehara, I; Fujii, T; Tanimoto, Y (Jan 2018). "Metabolic pathway of 6-aminohexanoate in the nylon oligomer-degrading bacterium Arthrobacter sp. KI72: identification of the enzymes responsible for the conversion of 6-aminohexanoate to adipate".Applied Microbiology and Biotechnology.102 (2):801–814.doi:10.1007/s00253-017-8657-y.PMID29188330.S2CID20206702.
