Nitrile rubber biodegradation by <i>Gordonia</i> sp. strain J1A and discovery of an oxygenase involved in its degradation

Acrylonitrile-butadiene rubber (NBR), which is a petroleum-derived synthetic copolymer composed of acrylonitrile and 1,3-butadiene, is used in large amounts around the world for disposable gloves and oil seals. Most of which are incinerated without being reused. We aimed to develop a bio-upcycling method for waste NBR (wNBR) and studied microorganisms capable of assimilating NBR. An NBR-degrading actinomycete, <i>Gordonia</i> sp. strain J1A, which degraded 6.5%-11% in weight loss of a wNBR sample in 10 days, was isolated from an activated sludge of an industrial wastewater treatment plant. We have found a membrane-bound nitrile rubber oxygenase (Nro1) as a key enzyme that catalyzes the initial reaction step of NBR decomposition. Nro1 showed high homology to the amino acid sequences of MpaB family proteins, but no similarity to those of natural rubber-degrading enzymes (latex clearing proteins: Lcps). The degradation products, such as 4-cyano-1-cyclohexene and C22-C58 NBR oligomers, containing aldehyde or ester, as well as carbon black, were detected through the enzymatic degradation of the wNBR sample by Nro1. These findings offer a new strategy for a bio-upcycling method of wNBR.IMPORTANCEAn actinomycete, <i>Gordonia</i> sp., utilized multiple acrylonitrile-butadiene rubber (NBR)-degrading enzymes to cleave the main-chain carbon-carbon (C-C and C=C) bonds of NBR, a petroleum-derived synthetic rubber. The degradation products, such as 4-cyano-1-cyclohexene and C22-C58 NBR oligomers, containing aldehyde or ester, were detected through the enzymatic degradation of a waste NBR (wNBR) sample. One of the NBR-degrading enzymes, nitrile rubber oxygenase (Nro1), showed high homology to the amino acid sequences of MpaB family proteins. This study provides new insights into the enzymatic degradation of the petroleum-derived synthetic polymers.