Abstract
Polystyrene (PS) is one of the main polymer types of plastic wastes and is known to be resistant to biodegradation, resulting in PS waste persistence in the environment. Although previous studies have reported that some microorganisms can degrade PS, enzymes and mechanisms of microorganism PS biodegradation are still unknown. In this study, we summarized microbial species that have been identified to degrade PS. By screening the available genome information of microorganisms that have been reported to degrade PS for enzymes with functional potential to depolymerize PS, we predicted target PS-degrading enzymes. We found that cytochrome P4500s, alkane hydroxylases and monooxygenases ranked as the top potential enzyme classes that can degrade PS since they can break C–C bonds. Ring-hydroxylating dioxygenases may be able to break the side-chain of PS and oxidize the aromatic ring compounds generated from the decomposition of PS. These target enzymes were distributed in Proteobacteria, Actinobacteria, Bacteroidetes, and Firmicutes, suggesting a broad potential for PS biodegradation in various earth environments and microbiomes. Our results provide insight into the enzymatic degradation of PS and suggestions for realizing the biodegradation of this recalcitrant plastic.
Highlights
Over 300 million tons of plastics were produced worldwide every year [1], only 21% of which has been recycled or incinerated, and the rest of plastic wastes are released into the environment [2]
Certain plastic-degrading microorganisms including bacteria and fungi were found in various environments such as marine MPs-associated biofilms [5], landfills [6], wastewater treatment plants [7], compost [8], guts of mealworms [9], mangrove sediment [10], etc
Monooxygenases were comprised of oxidoreductase, alkane 1-monooxygenase, cytochrome P450 alkane hydroxylase, etc. (Table S1)
Summary
Over 300 million tons of plastics were produced worldwide every year [1], only 21% of which has been recycled or incinerated, and the rest of plastic wastes are released into the environment [2]. Plastic waste undergoes gradual fragmentation into microplastics (MPs) or nanoplastics (NPs) through weathering, photolysis, abrasion, mechanical, and microbial decomposition, resulting in the ubiquity and persistence of plastic fragments in the environment [3]. Certain plastic-degrading microorganisms including bacteria and fungi were found in various environments such as marine MPs-associated biofilms [5], landfills [6], wastewater treatment plants [7], compost [8], guts of mealworms [9], mangrove sediment [10], etc While these studies reported the microbial consortium that can degrade synthetic polymers, they did not identify the microbial strains primarily responsible for the biodegradation of plastics [6,9,11]. An increasing number of microorganisms have been isolated and identified recently, the responsible enzymes or associated degradation pathways are rarely identified for many types of synthetic polymers
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