Microbial and Enzymatic Degradation of Synthetic Plastics

Abstract

Synthetic plastics are pivotal in our current lifestyle and therefore, its accumulation is a major concern for environment and human health. Petroleum-derived (petro-)polymers such as polyethylene (PE), polyethylene terephthalate (PET), polyurethane (PU), polystyrene (PS), polypropylene (PP), and polyvinyl chloride (PVC) are extremely recalcitrant to natural biodegradation pathways. Some microorganisms with the ability to degrade petro-polymers under in vitro conditions have been isolated and characterized. In some cases, the enzymes expressed by these microbes have been cloned and sequenced. The rate of polymer biodegradation depends on several factors including chemical structures, molecular weights, and degrees of crystallinity. Polymers are large molecules having both regular crystals (crystalline region) and irregular groups (amorphous region), where the latter provides polymers with flexibility. Highly crystalline polymers like polyethylene (95%), are rigid with a low capacity to resist impacts. PET-based plastics possess a high degree of crystallinity (30–50%), which is one of the principal reasons for their low rate of microbial degradation, which is projected to take more than 50 years for complete degraded in the natural environment, and hundreds of years if discarded into the oceans, due to their lower temperature and oxygen availability. The enzymatic degradation occurs in two stages: adsorption of enzymes on the polymer surface, followed by hydro-peroxidation/hydrolysis of the bonds. The sources of plastic-degrading enzymes can be found in microorganisms from various environments as well as digestive intestine of some invertebrates. Microbial and enzymatic degradation of waste petro-plastics is a promising strategy for depolymerization of waste petro-plastics into polymer monomers for recycling, or to covert waste plastics into higher value bioproducts, such as biodegradable polymers via mineralization. The objective of this review is to outline the advances made in the microbial degradation of synthetic plastics and, overview the enzymes involved in biodegradation.

Tenebrio molitor in the circular economy: a novel approach for plastic valorisation and PHA biological recovery

“…However, it should be noted that plastic degradation by TM could generate microplastics due to incomplete degradation and mineralisation. Microplastics harm the environment and human health since they attract and store toxic compounds, such as polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDs) and bisphenols (Mohanan et al 2020). Furthermore, all plastics contain various types of contaminants.…”

<em> </em>Current Research on Microbe-Plastic Interactions in the Marine Environment

“…(i) use multi-OMIC and interdisciplinary approaches to understand the role of the plastisphere in plastic biodegradation as well as in determining the mechanisms and pathways used for biodegradation 19,151,157,161,164,170,172,175,178,180,181,183,184,188,189,191,194,196,[198][199][200][204][205][206][207] ;…”

Multi-omics approach reveals new insights into the gut microbiome of Galleria mellonella (Lepidoptera:Pyralidae) exposed to polyethylene diet

“…Previous study on G. mellonella larvae gut states more than 80% of Enterococcus , however, only the midgut part of the digestive tract was used [36, 37]. Regarding the Proteobacteria, they were broadly abundant in the Pyralidae Plodia interpunctella [17]. It was interesting to observe that Ralstonia , Curvibacter and Herbaspirilum belong to three families among the most abundant in G.mellonella or P. interpunctella (Burkholderiaceae, Commamonadacea and Oxalobacteraceae).…”

“…The digestive tract of insects could be a new opportunity to track and characterize the proteins implicated in depolymerization of waste PE [17].…”

“…Some alkane hydroxylases, isolated from bacteria, have a pivotal role to hydrolyze the PE alkanes to release primary and secondary alcohols. The digestive tract of insects could be a new opportunity to track and characterize the proteins implicated in depolymerization of waste PE [17].…”