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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.
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]
For both bacterial and fungal plastivores, the first step is adhesion of spores to the plastic surface via hydrophobic interactions. [6]
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]
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]
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]
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]
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]
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]
Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging (plastic bags, plastic films, geomembranes and containers including bottles, cups, jars, etc.). As of 2017, over 100 million tonnes of polyethylene resins are being produced annually, accounting for 34% of the total plastics market.
Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity and do not rot easily. Chemically, lignins are polymers made by cross-linking phenolic precursors.
Polyethylene terephthalate (or poly(ethylene terephthalate), PET, PETE, or the obsolete PETP or PET-P), is the most common thermoplastic polymer resin of the polyester family and is used in fibres for clothing, containers for liquids and foods, and thermoforming for manufacturing, and in combination with glass fibre for engineering resins.
Polymer degradation is the reduction in the physical properties of a polymer, such as strength, caused by changes in its chemical composition. Polymers and particularly plastics are subject to degradation at all stages of their product life cycle, including during their initial processing, use, disposal into the environment and recycling. The rate of this degradation varies significantly; biodegradation can take decades, whereas some industrial processes can completely decompose a polymer in hours.
Mealworms are the larval form of the yellow mealworm beetle, Tenebrio molitor, a species of darkling beetle.
Waxworms are the caterpillar larvae of wax moths, which belong to the family Pyralidae. Two closely related species are commercially bred – the lesser wax moth and the greater wax moth. They belong to the tribe Galleriini in the snout moth subfamily Galleriinae. Another species whose larvae share that name is the Indianmeal moth, though this species is not available commercially.
Zophobas atratus is a species of darkling beetle, whose larvae are known by the common name superworm, kingworm, barley worm, morio worm or simply Zophobas. Superworms are common in the reptile pet industry as food, along with giant mealworms.
Tenebrio obscurus, or the dark mealworm beetle, is a species of darkling beetle whose larvae are known as mini mealworms. These insects should not be confused with younger mealworms or with the confused flour beetle.
Biodegradable plastics are plastics that can be decomposed by the action of living organisms, usually microbes, into water, carbon dioxide, and biomass. Biodegradable plastics are commonly produced with renewable raw materials, micro-organisms, petrochemicals, or combinations of all three.
In polymer chemistry photo-oxidation is the degradation of a polymer surface due to the combined action of light and oxygen. It is the most significant factor in the weathering of plastics. Photo-oxidation causes the polymer chains to break, resulting in the material becoming increasingly brittle. This leads to mechanical failure and, at an advanced stage, the formation of microplastics. In textiles the process is called phototendering.
Galleria mellonella, the greater wax moth or honeycomb moth, is a moth of the family Pyralidae. G. mellonella is found throughout the world. It is one of two species of wax moths, with the other being the lesser wax moth. G. mellonella eggs are laid in the spring, and they have four life stages. Males are able to generate ultrasonic sound pulses, which, along with pheromones, are used in mating. The larvae of G. mellonella are also often used as a model organism in research.
Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be molded, extruded or pressed into solid objects of various shapes. This adaptability, plus a wide range of other properties, such as being lightweight, durable, flexible, and inexpensive to produce, has led to their widespread use. Plastics typically are made through human industrial systems. Most modern plastics are derived from fossil fuel-based chemicals like natural gas or petroleum; however, recent industrial methods use variants made from renewable materials, such as corn or cotton derivatives.
Pestalotiopsis microspora is a species of endophytic fungus capable of breaking down and digesting polyurethane. Originally identified in 1880 in fallen foliage of common ivy in Buenos Aires, it also causes leaf spot in Hypericum 'Hidcote' shrubs in Japan.
Biodegradable additives are additives that enhance the biodegradation of polymers by allowing microorganisms to utilize the carbon within the polymer chain as a source of energy. Biodegradable additives attract microorganisms to the polymer through quorum sensing after biofilm creation on the plastic product. Additives are generally in masterbatch formation that use carrier resins such as polyethylene (PE), polypropylene (PP), polystyrene (PS) or polyethylene terephthalate (PET).
Exiguobacterium is a genus of bacilli and a member of the low GC phyla of Bacillota. Collins et al. first described the genus Exiguobacterium with the characterization of E. aurantiacum strain DSM6208T from an alkaline potato processing plant. It has been found in areas covering a wide range of temperatures (-12 °C—55 °C) including glaciers in Greenland and hot springs in Yellowstone, and has been isolated from ancient permafrost in Siberia. This ability to survive in varying temperature extremes makes them an important area of study. Some strains in addition to dynamic thermal adaption are also halotolerant, can grow within a wide range of pH values (5-11), tolerate high levels of UV radiation, and heavy metal stress.
The plastisphere is a human-made ecosystem consisting of organisms able to live on plastic waste. Plastic marine debris, most notably microplastics, accumulates in aquatic environments and serves as a habitat for various types of microorganisms, including bacteria and fungi. As of 2022, an estimated 51 trillion microplastics are floating in the surface water of the world's oceans. A single 5mm piece of plastic can host 1,000s of different microbial species. Some marine bacteria can break down plastic polymers and use the carbon as a source of energy.
Edible packaging refers to packaging which is edible and biodegradable.
Ideonella sakaiensis is a bacterium from the genus Ideonella and family Comamonadaceae capable of breaking down and consuming the plastic polyethylene terephthalate (PET) using it as both a carbon and energy source. The bacterium was originally isolated from a sediment sample taken outside of a plastic bottle recycling facility in Sakai City, Japan.
PETases are an esterase class of enzymes that catalyze the breakdown (via hydrolysis) of polyethylene terephthalate (PET) plastic to monomeric mono-2-hydroxyethyl terephthalate (MHET). The idealized chemical reaction is:
Plastic degradation in marine bacteria describes when certain pelagic bacteria break down polymers and use them as a primary source of carbon for energy. Polymers such as polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET) are incredibly useful for their durability and relatively low cost of production, however it is their persistence and difficulty to be properly disposed of that is leading to pollution of the environment and disruption of natural processes. It is estimated that each year there are 9-14 million metric tons of plastic that are entering the ocean due to inefficient solutions for their disposal. The biochemical pathways that allow for certain microbes to break down these polymers into less harmful byproducts has been a topic of study to develop a suitable anti-pollutant.
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