Biodegradation of micro sized nylon 6, 6 using Brevibacillus brevis a soil isolate for cleaner ecosystem

Abstract

The increasing accumulation of microplastic constitutes pathogens and hazardous chemicals posing a great threat to the ecosystem. Biodegradation is an eco-friendly strategy for the removal of these contaminants. The present investigation demonstrates bioremediation of nylon 6, 6 microplastics (NMPs) for the first time using a soil isolate called Brevibacillus brevis (B.brevis) by shake flask assay. 22 w/w % weight loss of nylon 6, 6 microplastics was noticed after 35 d of incubation with B.brevis. Upon interaction with microplastics, a change in the shape of the bacterium (rod to round) could be observed along with the size reduction of the microorganism. In the case of NMPs incubated in presence of this bacterium, irregular shapes of NMPs with cracks and holes could be visualized using SEM and TEM. TGA and FTIR analysis reported the disappearance of intermolecular hydrogen bonding of nylon 6, 6 posts microbial interaction. The release of various organic acids and enzyme/enzymatic activities of the bacterium was found to be higher in the presence of NMPs. The mass spectrometric analysis confirmed the release of adipic acid and hexamethylenediamine derivatives during aerobic biodegradation, indicating NMPs being the only carbon source for the growth of B.brevis in the reaction environment. The study addresses B.brevis as a viable bacterial source for the degradation of NMPs while at the same time attempting to understand the mechanism involved. A biodegradation pathway for B.brevis induced NMP degradation has been also proposed for the first time. This finding promises a potential approach for reducing the accumulation of nylon 6, 6 in the environment.