BACKGROUND: Wastes generated in production of caprolactam (2-oxohexamethylenimine, e-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 2.03.0 X 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 (c) 2012 Society of Chemical Industry