Chew on this: improved greater wax moth genome gives insight into plastic biodegradation

Biodegradation is currently the most eco-friendly approach to breaking down complex plastic into less harmful products. Luckily, a number of insects and microorganisms have the capability to digest plastic polymers, and several studies have shown that insect guts can biodegrade plastics faster than environmental microbes. To tackle the global—and mounting—plastic waste problem, researchers look to these critters in hopes of adapting their enzymatic capabilities into efficient systems that can degrade plastic waste at scale.

In a recent study published in the June issue of G3: Genes, Genomes, Genetics, Young et al. report an improved reference genome for the greater wax moth Galleria mellonella as a tool to identify enzymatic pathways with plastic biodegradation properties.

Well-known as a honeybee pest, greater wax moth larvae feed on beeswax, which contains long-chain hydrocarbons. Since long-chain hydrocarbons are also the major constituent in polyethylene (PE), researchers are quite interested in the enzymes responsible for beeswax degradation; in fact, the hexamerin and arylphorin proteins, found in larval saliva, have demonstrated PE-degrading abilities. Evidence suggesting wax moth larvae can degrade other plastics like polystyrene and polypropylene makes them attractive for plastic biodegradation research. The extent to which moth larvae possess plastic catabolizing enzymes is unclear; however, since both the larvae themselves and their gut microbiota have been implicated in PE biodegradation.

Since the existing reference genome for G. mellonella was fragmented, Young et al. combined short- and long-read sequencing approaches to generate a new assembly with improved continuity, identifying an additional 3,000 mRNA sequences. This new reference genome also supported phylogenetic comparisons with other Lepidoptera members such as moths, butterflies, and silkworms, allowing the authors to begin constructing an understanding of the evolutionary history of PE-degrading enzymes in winged insects.

Secreted proteins have a much better chance of playing a role in long-chain hydrocarbon degradation than intracellular proteins, so the authors investigated 3,865 proteins identified as secreted in their assembly, finding numerous hydrolases, transferases, oxidoreductases, ligases, lyases, and isomerases. They propose that these secretory enzymes, which may have evolved to catabolize a variety of exogenous and insoluble polymers, must also be capable of processing long-chain polymers like polyethylene. Several of the identified hydrolases and oxidoreductases are members of enzyme classes known to degrade plastic. They also found 135 hydrolases and 10 oxidoreductases that are predicted to act on ester bonds and peroxide, which may make them capable of breaking polyethylene. This genome is one of many sequenced by the Applied Genomics Initiative at the Commonwealth Scientific and Industrial Research Organisation in Australia. The initiative aims to sequence the genomes of a variety of organisms of interest to enable translational research in areas such as conservation, biosecurity, and health. The improved reference genome for the greater wax moth will continue to aid researchers in uncovering the molecular mechanisms behind its ability to degrade long-chain hydrocarbons; hopefully, these larvae can become a powerhouse for developing industrial and bioremediation applications in reducing plastic waste.