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Plastivore

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Mealworms, an example of a plastivore

A plastivore is an organism capable of degrading and metabolising plastic.[1][2][3][4] While plastic is normally thought of as non-biodegradable, a variety of bacteria, fungi and insects have been found to degrade it.

Definition

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Plastivores are "organisms that use plastic as their primary carbon and energy source".[3] This does not necessarily mean being able to fulfill all biological needs from plastic alone. For example, mealworms fed only on plastic show very little weight gain, unlike mealworms fed on a normal diet of bran.[5] This is due to plastic lacking water and nutrients needed to grow.[5] Plastic-fed mealworms can still derive energy from their diet, so they do not lose weight like starved mealworms do.[5]

Mechanisms

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For both bacterial and fungal plastivores, the first step is adhesion of spores to the plastic surface via hydrophobic interactions.[6]

Diagram showing how Ideonella sakaiensis metabolises plastic

Bacterial plastivores, when cultured on plastic, form biofilms on the surface as the second step.[7][8][9] Using enzymes, they increase the roughness of the surface and oxidize the plastic.[7][8][9] Oxidation forms oxygenated groups such as carbonyl groups, used by the bacteria for carbon and energy, and also converts the plastic into smaller molecules (depolymerization).[7][8]

For fungal plastivores, the second step is growth of mycelia (root-like structures of fungi, composed of thread-like hyphae) on the surface, while the third step is secretion of enzymes.[6] Both the enzymes as well as the mechanical force produced by fungal hyphae degrades the plastic.[6]

The same basic steps of oxidation and depolymerization also occur in insect plastivores.[10] For insects, the bacteria in their guts plays a role in digesting plastic. In mealworms, inhibiting these bacteria by giving antibiotics removes the ability to digest polystyrene, but low-density polyethylene can still be digested to an extent.[9][10] The insects themselves also play a role: saliva of waxworms contains enzymes that oxidize and depolymerize polyethylene.[11]

Examples

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The following is not an exhaustive list. Plastivorous activity seems to be quite common in nature, with a 2011 sampling of endophytic fungi in the Amazon finding that almost half of the fungi showed some activity.[12]

Bacteria

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Further information: Plastic degradation by marine bacteria

The plastic pollution in the oceans supports many species of bacteria.

The alkaliphilic bacteria Bacillus pseudofirmus and Salipaludibacillus agaradhaerens can degrade low-density polyethylene (LDPE). These bacteria can degrade LDPE on their own but work more quickly as a consortium of both species, and degradation is faster still when iron oxide nanoparticles are added.[7]

Exiguobacterium sibiricum and E. undae, isolated from a wetland in India, can degrade polystyrene.[8] Similarly, Exiguobacterium sp. strain YT2 has been isolated from the gut of mealworms, which are themselves plastivores, and can degrade polystyrene on its own, though less quickly than mealworms.[9]

Acinetobacter sp. AnTc-1, isolated from the gut of plastivorous red flour beetle larvae, can likewise degrade polystyrene on its own.[13]

Ideonella sakaiensis and Comamonas testosteroni can degrade polyethylene terephthalate.[14][15]

Fungi

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Aspergillus tubingensis and several isolates of Pestalotiopsis are capable of degrading polyurethane.[6][12]

Polycarbonate, the main material in CDs, is attacked by a range of fungi: Bjerkandera adusta[16] (initially misidentified as Geotrichum sp.[17]), Chaetomium globosum, Trichoderma atroviride, Coniochaeta sp., Cladosporium cladosporioides and Penicillium chrysogenum.[18]

Insects

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Mealworms (Tenebrio molitor), a species commonly used as animal feed, can consume polyethylene and polystyrene.[5][9][10] Its congener T. obscurus can also consume polystyrene,[19] as can superworm (Zophobas morio) and red flour beetle (Tribolium castaneum) from different genera in the same family.[20][13]

A waxworm

Plastivory also occurs in Lepidoptera, with waxworms (Galleria mellonella) able to consume polyethylene.[11][21] Even homogenising waxworms and applying the homogenate to polyethylene can cause degradation.[21] This species is the fastest known organism to chemically modify polyethylene, with oxidation occurring within one hour from exposure.[11]

References

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  1. ^ Boctor, Joseph (2024). "Nature's Plastic Predators: A Comprehensive and Bibliometric Review of Plastivore Insects". Polymers. 16 (12): 1671. doi:10.3390/polym16121671. PMC 11207432. PMID 38932021.
  2. ^ "Plastivores: Plastic-Degrading Super-Microbes and Enzymes". Wyss Institute. 2023-10-19. Retrieved 2024-02-26.
  3. ^ a b "Why scientists say 'plastivores' could be the solution to plastic pollution". WHYY. Retrieved 2024-02-26.
  4. ^ Yirka, Bob; Phys.org. "The caterpillar larvae 'plastivores' that consume and metabolize polyethylene". phys.org. Retrieved 2024-02-26.
  5. ^ a b c d Yang, Yu; Yang, Jun; Wu, Wei-Min; Zhao, Jiao; Song, Yiling; Gao, Longcheng; Yang, Ruifu; Jiang, Lei (2015-10-20). "Biodegradation and Mineralization of Polystyrene by Plastic-Eating Mealworms: Part 1. Chemical and Physical Characterization and Isotopic Tests". Environmental Science & Technology. 49 (20): 12080–12086. Bibcode:2015EnST...4912080Y. doi:10.1021/acs.est.5b02661. ISSN 0013-936X. PMID 26390034.
  6. ^ a b c d Khan, Sehroon; Nadir, Sadia; Shah, Zia Ullah; Shah, Aamer Ali; Karunarathna, Samantha C.; Xu, Jianchu; Khan, Afsar; Munir, Shahzad; Hasan, Fariha (2017). "Biodegradation of polyester polyurethane by Aspergillus tubingensis". Environmental Pollution. 225: 469–480. Bibcode:2017EPoll.225..469K. doi:10.1016/j.envpol.2017.03.012. PMID 28318785.
  7. ^ a b c d G. Cada, Erika Joy (June 2019). "Enhanced in vitro biodegradation of low-density polyethylene using alkaliphilic bacterial consortium supplemented with iron oxide nanoparticles" (PDF). Philippine Science Letters. 12.
  8. ^ a b c d Chauhan, Deepika; Agrawal, Guncha; Deshmukh, Sujit; Roy, Susanta Sinha; Priyadarshini, Richa (2018). "Biofilm formation by Exiguobacterium sp. DR11 and DR14 alter polystyrene surface properties and initiate biodegradation". RSC Advances. 8 (66): 37590–37599. Bibcode:2018RSCAd...837590C. doi:10.1039/C8RA06448B. ISSN 2046-2069. PMC 9089450. PMID 35558609.
  9. ^ a b c d e Yang, Yu; Yang, Jun; Wu, Wei-Min; Zhao, Jiao; Song, Yiling; Gao, Longcheng; Yang, Ruifu; Jiang, Lei (2015-10-20). "Biodegradation and Mineralization of Polystyrene by Plastic-Eating Mealworms: Part 2. Role of Gut Microorganisms". Environmental Science & Technology. 49 (20): 12087–12093. Bibcode:2015EnST...4912087Y. doi:10.1021/acs.est.5b02663. ISSN 0013-936X. PMID 26390390.
  10. ^ a b c Yang, Li; Gao, Jie; Liu, Ying; Zhuang, Guoqiang; Peng, Xiawei; Wu, Wei-Min; Zhuang, Xuliang (2021). "Biodegradation of expanded polystyrene and low-density polyethylene foams in larvae of Tenebrio molitor Linnaeus (Coleoptera: Tenebrionidae): Broad versus limited extent depolymerization and microbe-dependence versus independence". Chemosphere. 262: 127818. Bibcode:2021Chmsp.26227818Y. doi:10.1016/j.chemosphere.2020.127818. PMID 32771707. S2CID 224882094.
  11. ^ a b c Sanluis-Verdes, A.; Colomer-Vidal, P.; Rodriguez-Ventura, F.; Bello-Villarino, M.; Spinola-Amilibia, M.; Ruiz-Lopez, E.; Illanes-Vicioso, R.; Castroviejo, P.; Aiese Cigliano, R.; Montoya, M.; Falabella, P.; Pesquera, C.; Gonzalez-Legarreta, L.; Arias-Palomo, E.; Solà, M. (2022-10-04). "Wax worm saliva and the enzymes therein are the key to polyethylene degradation by Galleria mellonella". Nature Communications. 13 (1): 5568. Bibcode:2022NatCo..13.5568S. doi:10.1038/s41467-022-33127-w. ISSN 2041-1723. PMC 9532405. PMID 36195604.
  12. ^ a b Russell, Jonathan R.; Huang, Jeffrey; Anand, Pria; Kucera, Kaury; Sandoval, Amanda G.; Dantzler, Kathleen W.; Hickman, DaShawn; Jee, Justin; Kimovec, Farrah M.; Koppstein, David; Marks, Daniel H.; Mittermiller, Paul A.; Núñez, Salvador Joel; Santiago, Marina; Townes, Maria A. (2011). "Biodegradation of Polyester Polyurethane by Endophytic Fungi". Applied and Environmental Microbiology. 77 (17): 6076–6084. Bibcode:2011ApEnM..77.6076R. doi:10.1128/AEM.00521-11. ISSN 0099-2240. PMC 3165411. PMID 21764951.
  13. ^ a b Wang, Zhe; Xin, Xin; Shi, Xiaofan; Zhang, Yalin (2020-07-15). "A polystyrene-degrading Acinetobacter bacterium isolated from the larvae of Tribolium castaneum". Science of the Total Environment. 726: 138564. Bibcode:2020ScTEn.72638564W. doi:10.1016/j.scitotenv.2020.138564. ISSN 0048-9697. PMID 32315854. S2CID 216075743.
  14. ^ Yoshida, Shosuke; Hiraga, Kazumi; Takehana, Toshihiko; Taniguchi, Ikuo; Yamaji, Hironao; Maeda, Yasuhito; Toyohara, Kiyotsuna; Miyamoto, Kenji; Kimura, Yoshiharu; Oda, Kohei (2016-03-11). "A bacterium that degrades and assimilates poly(ethylene terephthalate)". Science. 351 (6278): 1196–1199. Bibcode:2016Sci...351.1196Y. doi:10.1126/science.aad6359. ISSN 0036-8075. PMID 26965627. S2CID 31146235.
  15. ^ Gong, Jixian; Kong, Tongtong; Li, Yuqiang; Li, Qiujin; Li, Zheng; Zhang, Jianfei (2018-11-30). "Biodegradation of Microplastic Derived from Poly(ethylene terephthalate) with Bacterial Whole-Cell Biocatalysts". Polymers. 10 (12): 1326. doi:10.3390/polym10121326. ISSN 2073-4360. PMC 6401706. PMID 30961251.
  16. ^ Romero, Elvira; Speranza, Mariela; García-Guinea, Javier; Martínez, Ángel T.; Martínez, María Jesús (2007). "An anamorph of the white-rot fungus Bjerkandera adusta capable of colonizing and degrading compact disc components". FEMS Microbiology Letters. 275 (1): 122–129. doi:10.1111/j.1574-6968.2007.00876.x. hdl:10261/47650. PMID 17854471.
  17. ^ Garcia-Guinea, Javier; Cárdenes, Victor; Martínez, Angel T.; Martínez, Maria (2001). "Fungal bioturbation paths in a compact disk". Naturwissenschaften. 88 (8): 351–354. Bibcode:2001NW.....88..351G. doi:10.1007/s001140100249. ISSN 0028-1042. PMID 11572018. S2CID 7599290.
  18. ^ Palermo, Anna M.; Gentile, Antonio; Pellegrino, Giuseppe (2021). "Documentary heritage: fungal deterioration in Compact Discs". Heritage Science. 9 (1). doi:10.1186/s40494-021-00609-x. ISSN 2050-7445.
  19. ^ Peng, Bo-Yu; Su, Yiming; Chen, Zhibin; Chen, Jiabin; Zhou, Xuefei; Benbow, Mark Eric; Criddle, Craig S.; Wu, Wei-Min; Zhang, Yalei (2019-05-07). "Biodegradation of Polystyrene by Dark ( Tenebrio obscurus ) and Yellow ( Tenebrio molitor ) Mealworms (Coleoptera: Tenebrionidae)". Environmental Science & Technology. 53 (9): 5256–5265. Bibcode:2019EnST...53.5256P. doi:10.1021/acs.est.8b06963. ISSN 0013-936X. PMID 30990998. S2CID 119102958.
  20. ^ Sun, Jiarui; Prabhu, Apoorva; Aroney, Samuel T. N.; Rinke, Christian (2022-06-30). "Insights into plastic biodegradation: community composition and functional capabilities of the superworm (Zophobas morio) microbiome in styrofoam feeding trials". Microbial Genomics. 8 (6). doi:10.1099/mgen.0.000842. ISSN 2057-5858. PMC 9455710. PMID 35678705.
  21. ^ a b Bombelli, Paolo; Howe, Christopher J.; Bertocchini, Federica (2017). "Polyethylene bio-degradation by caterpillars of the wax moth Galleria mellonella". Current Biology. 27 (8): R292–R293. Bibcode:2017CBio...27.R292B. doi:10.1016/j.cub.2017.02.060. hdl:10261/164618. PMID 28441558.
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