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like graphene7, which shows potential therefore provide a deeper insight into References as a transparent conductive electrode structural and electronic properties of 1. Hlawacek, G. et al. Science 321, 108–111 (2008). 10 2. Goiri, E. et al. Phys. Rev. Lett. 112, 117602 (2010). with superior flexibility for organic heteromolecular phases . Accessing the 3. Henneke, C., Felter, J., Schwarz, D., Tautz, F. S. & Kumpf, C. optoelectronics. Indeed, recent LEEM phase diagram itself is beyond the scope Nat. Mater. 16, 628–633 (2017). observations of CuPc deposited on graphene of standard DFT, but ab initio atomistic 4. Schmidt, Th. et al. Ultramicroscopy 110, 1358–1361 (2001). 5. Huang, Y. L. et al. Small 6, 70–75 (2010). 8 11 indicate 2D lattice gas formation , due to the thermodynamics calculations might 6. Huang, H., Huang, Y., Pflaum, J., Wee, A. & Chen, W. Appl. Phys. same repulsive intermolecular interaction as provide complementary support to account Lett. 95, 263309 (2009). 7. Hlawacek, G., Khokhar, F. S., van Gastel, R., Poelsema, B. on Ag(111). for such a complicated coexistence of up & Teichert, C. Nano Lett. 11, 333–337 (2011). The work also opens a new field of to two crystalline molecular phases with a 8. Schwarz, D., Henneke, C. & Kumpf, C. New. J. Phys. activity for theoretical studies. In fact, 2D lattice gas. ❐ 18, 0234703 (2016). 9. Langreth, D. C. et al. J. Phys. Condens. Matter 21, 084203 (2009). the density functional theory (DFT) 10. Stadtmüller, B. et al. Nat. Commun. 5, 3685 (2014). community has already been accounting Christian Teichert is at the Institute of Physics of the 11. Reuter, K. & Scheffler, M. Phys. Rev. Lett. 90, 046103 (2003). for van der Waals interactions in Montanuniversitaet Leoben, Leoben 8700, Austria. organic thin film growth9; it may e-mail: [email protected] Published online: 13 March 2017 MATERIAL WITNESS PLASTICS ON THE MENU

The ability of moth caterpillars to are also fungi that can biodegrade digest polyethylene, reported recently plastics, such as the species by Bombelli and colleagues1, has Pestalotiopsis microspora, which awakened fresh interest in using infests plants in South America enzymes to break down plastic waste, and Asia and is able to break and perhaps even to convert it to down polyurethane4. useful materials. The demand for such Given these precedents, the a process is clear. Millions of tonnes of discovery that the greater wax moth plastics are discarded worldwide every Galleria mellonella can devour year, much of it in packaging. Only LDPE — it was serendipitously a small proportion is recycled, and found to chew holes in plastic carrier PHILIP BALL much ends up in landfill — or worse, bags — seems less surprising1. Wax as pollution dumped in the natural moths, which are known throughout hope that the discovery might lead to environment. The most common types the world, are so called because of a viable biotechnological solution to of plastic in waste, such as high- and the propensity of their larvae to feed plastic waste. low-density polyethylene (H/LDPE), on the wax of honeybee combs: a But a solution need not be polypropylene, polyvinylchloride and threat against which beekeepers must bio-inspired. The alternative of polyethylene terephthalate (PET), take careful precautions. Wax being developing purely synthetic catalysts break down only very slowly: some can made from long-chain hydrocarbons that break down plastics, ideally to take centuries, especially if buried and (primarily aliphatic esters), it stands useful substances such as hydrocarbon hidden from ultraviolet light. to reason that the larval digestive fuels, also looks viable in principle. For The consequences are well system can handle polyethylene too. example, Jia et al. have shown that two rehearsed: not just a defacing of The polymer is degraded to catalysts working in tandem, originally the environment, but a hazard to ethylene glycol, potentially a useful developed to link short hydrocarbons wildlife, with sea creatures ingesting chemical feedstock. And the rate of into longer ones for fuel production, or becoming entangled in plastic. degradation — a single worm can eat can also degrade polyethylene into Most soil and marine bacteria have no through about 1 mg in 12 hours — is such long-chain fuel hydrocarbons in impact on such plastics. rather greater than that found for the presence of smaller hydrocarbon But plastic-degrading previous microbial processes. It isn’t molecules5. The process isn’t microorganisms do exist. One yet clear if the enzymes responsible are commercially viable yet, but it reminds such was identified by Yoshida and produced by the caterpillars themselves us that nature’s ingenuity shouldn’t co-workers2: through screening of or reside in their gut microbiome. The blind us to our own. ❐ natural microbial communities found latter possibility might conceivably be on PET debris at a bottle recycling the more promising, especially if the References facility, they discovered a bacterium metabolic pathway turns out to involve 1. Bombelli, P., Howe, C. J. & Bertocchini, F. Curr. Biol. 27, R283–R293 (2017). named Ideonella sakaiensis, which more than one enzyme, since then the 2. Yoshida, S. et al. Science 351, 1196–1199 (2016). can metabolize the plastic. Microbes bacteria concerned might be cultivated 3. Yang, J., Yang, Y., Wu, W.-M., Zhao, J. & Jiang, L. that break down polyethylene have as integrated plastic-degradation Environ. Sci. Technol. 48, 13776–13784 (2014). 4. Russell, J. R. et al. Appl. Environ. Microbiol. also been found in the gut flora units rather than having to cope with 77, 6076–6084 (2011). of the larval Indian mealmoth a multistep process in a free-enzyme 5. Jia, X., Qin, C., Friedberger, T., Guan, Z. & Huang, Z. Plodia interpunctella3. And there reactor. Either way, Bombelli et al. Sci. Adv. 2, e1501591 (2016).