Exploring microbial degradation of polyamide 4 in soils: Unveiling degradation mechanisms, pathways, and the contribution of strain NR4

Abstract

Evidence for microbial degradation of polyamide 4 (PA4) has previously been reported, but little is available on the specific strains and enzymes. The mechanism responsible for the degradation is still unknown. This study investigated the degradation behaviors of PA4 films in composted, garbage and campus soil. Various characterization methods were used to evaluate the changes in morphology, structure, crystallinity, and thermal properties of PA4 films during the soil biodegradation, to assess its degradation efficiency in four types of soils. The results showed that the highest degradation behavior of soil in composted soil that almost no residual films can be observed in this type of soil after 60 days, compared to those in garbage and campus soil. PA4 degradation resulting occurring in soils can enhance the population of certain beneficial microorganisms in the soil environment, such as Ensifer, Luteimonas, etc., which play a key role in nitrogen fixation, promoting plant growth, and carbon cycling. Moreover, a highly efficient single bacterium for PA4 degradation was isolated from the soil enriched and acclimated by PA4 films, named strain NR4. The complete genome of strain NR4 was sequenced to identify relevant enzyme-coding genes and metabolic pathways associated with PA4 degradation, ultimately leading to the proposal of a mechanism for PA4 biodegradation. The research not only examined how PA4 degrades in different types of soil but also suggested practical recommendations for promoting biodegradation of other products in the nylon family. The results obtained from the current study are essential in addressing environmental issues surrounding the buildup of non-biodegradable nylon items in the ecosystem.