Biodegradation of polyamide 4 in seawater

Herein, we report on the aquatic degradation of polyamide (nylon) 4. Polyamide 4 (PA4) has previously been shown to degrade in natural environments such as activated sludge and soil, as well as in vivo (when subcutaneously implanted in the backs of rats). In laboratory biodegradation tests of PA4, polyhydroxybutyrate (PHB), and polycaprolactone (PCL) in sampled seawater, the amount of oxygen absorption increased over time. PA4 degraded by about 30% in 4 weeks, which is comparable to that of PCL (30%) but less than that of PHB (60%). PA4 films were immersed in the sea and recovered at adequate intervals and weighed. The weight of the films decreased by 10–70% in 6 weeks, showing that PA4 is degraded in actual aquatic (sea) environments. We isolated PA4-degrading bacteria, strain MND-1, from the seawater used in the laboratory degradation tests. MND-1 is thought to belong to the family Alteromonadaceae from the DNA sequence of 16S rDNA. Gamma-aminobutyric acid (GABA) and GABA oligomers were detected in the PA4 degradation products. This indicates that the strain MND-1 hydrolyzes the amide bonds of PA4 into GABA oligomers and GABA.