22 - Microplastic degradation by bacteria in aquatic ecosystem

Abstract

The unorganized and mismanaged applications of plastics and their products for countless purposes in villages, towns, and metropolitan cities end up deposited in the aquatic environment. Plastic bags take approximately 1000 years to decompose. The detection and quantification of microplastics has increased in aquatic environments and there is emergent alarm about the potential effects on micro- and macroflora and -fauna. The polyethylenes, like LDPE, MDPE, HDPE, LLDPE and poly(butylene terephthalate), nylons, polypropylene, polystyrene, polyvinyl chloride, polyurethane, polyethylene terephthalate, are synthetic plastics and buoyant in water. Unindustrialized toxins generated due to the chemical reactions of microplastics accumulate in sediments and cause ecological hazards to the benthic communities of the aquatic environment. Tiny granules of plastics smaller than 5mm are used in cosmetics as scrubbers, mouth wash, air blasting, and hand cleaners and are normally denoted as nano/microplastic. Uncertain consequences have been seen for the health of the living organism due to ingestion of tiny nano/microplastics by lower trophic fauna. Most common fragments and fibers (800–1600μm) of microplastics collected from the field have been reported in various aquatic animals. Degradation of various types of microplastics has been reported by several bacteria, such as Bacillus sp. BCBT21, Bacillus amyloliquefaciens BSM-1, B. amyloliquefaciens BSM-2, Pseudomonas putida, Bacillus subtilis, Bacillus cereus, Brevibaccillus borstelensis, Bacillus vallismortis bt-dsce 01, P. protegens bt-dsce 02, Stenotrophomonas sp. bt-dsce03, and Paenibacillus sp.bt-dsce04. Extracellular hydrolytic enzymes such as CMCase, lipase, xylanase, keratinase, chitinase, and protease secreted by these bacteria play a charismatic role in plastic degradation. Polyurethane depolymerizes the urethane and ester bonds due to the hydrolytic properties of urease, esterase, and proteases enzymes. Papain and urease have capabilities to degrade medical polyesters due to their proteolytic properties. This chapter demonstrates that the degradation of microplastics by microorganisms in aquatic environments reduces the ecological risk of microplastic pollution.