Transformation of low‐molecular linear caprolactam oligomers by caprolactam‐degrading bacteria

Abstract

AbstractBACKGROUND: Wastes generated in production of caprolactam (2‐oxohexamethylenimine, ε‐caprolactam) and caprolactam‐based polymers contain the unreacted monomer and its low‐molecular linear and cyclic oligomers. Application of microorganisms for biological treatment of caprolactam‐ and oligomer‐containing wastes can become an alternative to existing waste utilization methods. This work investigated the transformation of caprolactam low‐molecular linear oligomers by caprolactam‐degrading bacteria bearing degradative plasmids (CAP plasmids).RESULTS Based on mass spectrometry data, a scheme for the biotransformation of caprolactam linear oligomers is proposed. Oxidative transamination to corresponding dicarboxylic acids can be one of the transformation mechanisms. Oxidative transamination occurs due to a broad substrate specificity of the caprolactam catabolism key enzymes 2‐oxoglutarate‐6‐aminohexanoate transaminase (EC.2.6.1‐) and 6‐oxohexanoate dehydrogenase (EC.1.2.1.63) whose synthesis is determined by CAP plasmids. Incubation of cells 2.0–3.0 × 109 CFU mL−1 of strains with various plasmid‐bacterial host combinations in 2 mmol L−1 solution of a dimer for 96 h leads to its almost complete transformation to a corresponding dicarboxylic acid. The dynamics of the process largely depends on the host strain.CONCLUSION: Deamination of oligomers in their transformation by the enzyme systems of caprolactam‐degrading bacteria can substitute the chemical methods of pretreating caprolactam‐ and oligomer‐containing wastes for their subsequent biological purification. Copyright © 2012 Society of Chemical Industry