"The rapid biodegradation of plastics in the intestine of Tenebrio reveals a new fate of discarded plastic waste in the environment," said Professor Yang Jun of Beijing University of Aeronautics and Astronautics. Plastics are difficult to degrade naturally in the environment, and polystyrene is one of them. Due to high molecular weight and high stability, it is generally believed that microorganisms cannot degrade polystyrene plastics. In 2015, Prof. Yang Jun of the Beijing University of Aeronautics and Astronautics and Dr. Zhao Wei of Shenzhen Huada Gene Company jointly published two sister research papers on Environmental Science & Technology, an authoritative journal in the field of environmental science, demonstrating Tenebrio (bread Larvae of insects can degrade polystyrene, the most difficult to degrade plastic.
The picture shows plastic mealworms (instructed by Professor Yang Jun)
The breakthrough study showed that with Styrofoam as the sole food source, Tenebrio molitor larvae can survive for more than 1 month and eventually develop into adults. The polystyrene they eat is fully degraded, mineralized to CO2 or assimilated. Body fat. This discovery provides ideas for solving global plastic pollution problems.
In spite of this, in the face of growing white plastic pollution, Prof. Yang Jun also called for the public to use less disposable plastic lunch boxes and convenient bags in daily life.
Dilemma
Degradable plastic into a world problem
The pollution of plastic waste from petrochemical production is a world environmental problem. Most plastic disposables are discarded after they are used. Until now, academia believes that plastic products will not be decomposed for tens to hundreds of years in the natural environment due to their stable physical and chemical structure.
Prof. Yang Jun introduced that in 2013, the world consumed 299 million tons of plastics, of which polystyrene plastics accounted for 7%, and consumed about 21 million tons each year. Commonly used plastic lunch boxes, coffee cups and other materials that can withstand the boiling water temperature are polystyrene. . Authoritative surveys have shown that polystyrene, a plastic that degrades in the soil, sludge, decayed waste, or manure microbial community, only degrades by 0.01%-3% in 4 months.
Every year, 40 million tons of waste plastics in the world are accumulated in the environment. About 2 million tons of waste plastics are lost to the environment each year in China. Taking the agricultural film for farmland as an example, the annual output of agricultural film in China reaches 1 million tons and increases at a rate of 10% per year. No matter what kind of crop is covered, all film-covered soil has residual film. According to statistics, the annual residual quantity of agricultural film in China is as high as 350,000 tons, the remaining film rate is 42%, and a large amount of residual film remains in the farmland of 0-30 cm in farmland. In other words, nearly half of the agricultural film remains in the soil, which is a great hidden danger in food safety.
"Plastics are completely assimilated by microorganisms in the soil, and degradation into CO2 and water to achieve inorganic mineralization may take 200-400 years, resulting in accumulation in the environment." Professor Yang Jun told the Yangcheng Evening News reporter.
Chiss
Brain hole opened, please help insects
Since 2005, Yang Jun team began to study the biodegradation of plastics. The main attack is the most difficult degradation of polystyrene and other plastics degradation.
Scientists had previously used several soil invertebrate experiments such as earthworms, millipedes, cockroaches, and snails to see if they could eat plastic. When 14C-labeled plastics such as polyvinyl chloride (PVC), polyethylene (PE) and polypropylene (PP) were fed, the results showed no degradation.
Yang Jun believes that the idea of ​​biodegradable plastics must be developed. It should not be confined to microorganisms. Lepidopteran insects, termites, etc. can be considered. Marine rafts and boreholes can erode polyethylene and submarine cables. The organism separates and clones key enzymes and genes that produce active groups.
A 2014 study by the Yang Jun team found that the waxworm (Indian maggot larva) was able to chew and feed polyethylene PE film. The larvae isolated two strains that could degrade the PE film, namely Enterobacter YT1 and Bacillus YP1. The team then discovered that Tenebrio larvae are a more powerful animal that eats plastic. They are larger than the waxworm (usually 35 mm long and 3 mm wide) and can use foam as the only food. Tenebrio have 4 life stages: eggs, larvae, cockroaches and adults.
Tenebrio, also known as breadworms, belong to Coleoptera in terms of insect taxonomy, and are intended to be legumes and beetles (p. Originating in North America, the former Soviet Union imported Chinese from the former Soviet Union in the 1950s, and Tenebrio is known as the "protein feed bank." Its dried products contain 30% fat, containing up to 50% more protein, in addition to phosphorus, potassium, iron and other elements. The dried worm larvae contained about 40% protein, 57% larvae, and 60% adults.
In China, Tenebrio is actually similar to silkworm, and humans can eat it directly, eat it fry, and use it as a feed. The mealworms, cockroaches, cockroaches, snakes, tropical fish, and goldfish eaten by the mealworms are not only fast-growing but also alive. The rate is high, and the disease resistance is strong, and the fertility is also greatly improved. Cultivation of Tenebrio is very easy, farmers can use fresh oats, wheat bran, apple breeding.
Surprise
Insects really eat plastic!
Prof. Yang Jun’s team purchased polystyrene plastic raw materials from Sinopec Yanshan Branch. There are no additives or catalysts in these raw materials. The α-13C, β-13C-labeled polystyrene plastic samples were purchased from the United States. Tenebrio are purchased from insect breeding farms in Daxing, Beijing and Qinhuangdao, Hebei, and are fed with grain. These insects are located at 3-4 instars (ie faded 3-4 times).
These mealworms were placed in a polypropylene plastic container with foam blocks. The experimenter regularly measured the weight of foam blocks eaten by Tenebrio molitor. The control group was normal meal fed with wheat bran. In the experiment, 500 Tenebrio molitors were the only food with 5.8 grams of foam, and were kept in a greenhouse under controlled conditions ( 25±1°C, 80±2% humidity, and 16:8 light/dark cycles). During the incubation process, the dead mealworms were immediately removed.
In the experiment, Yang Jun et al. fed the larvae of Tenebrio molitor using foam plastic as a single food source. Comparing normal feeding (feeding bran) with dying larvae, it was found that the dry weight of the larvae did not increase significantly (+33.6%) compared to normal feeding larvae during the 16-day experimental period, but increased by only a small amount by 0.2% ( This is due to the lower water content and nutritional value of the foam compared to bran) but not as much as the dry weight of the dying larvae (-24.9%), and the survival rate of the larvae in the fed plastic and bran groups. There is no significant difference.
100 Mealworms can eat 34-39 mg of foam per day. During the 16-day experimental period, 47.7% of the foam ingested by the insects was converted to CO2. Residues (about 49.2%) were converted to biodegradable particles resembling rabbit feces and excreted. Tests with alpha-13C or beta-13C-labeled polystyrene plastics confirmed their mineralization as carbon-13 labeled carbon dioxide and lipids. Polystyrene foam in the gut of the larvae degrades in less than 24 hours.
The larvae that use Styrofoam as the only food, and those that have been fed with the normal food (wheat bran), have developed a crustacean like a healthy one after 1 month. Tenebrio eats a hole in the foam. After passing through the insect's intestine, the chemical structure and composition of the ingested foam changes. By using gel permeation chromatography (GPC), nuclear magnetic resonance spectroscopy of carbon-13, and TG-FTIR spectroscopy, it was confirmed that the breakdown of long-chain polystyrene molecules in the larvae intestinal tract formed metabolites of insects and excreted as feces.
The experiment further succeeded in isolating the polystyrene-degrading bacterium, Ext. YT2 (Exiguobacterium sp. YT2), which can use the polystyrene as the sole carbon source to grow in the gut of larvae. The strain has been preserved in the General Microbiology Center and the National Gene Bank of China's Microbial Culture Collection Management Committee. It is the first polystyrene-degrading bacterium that has been reported in the world to be preserved at the center of the strain.
potential
Tenebrio eat all plastic
The research team gave the mechanism that the yellow-powdered larvae rode to degrade the polystyrene: In the first step, the foam was first chewed by the yellow-powder larvae into small pieces and taken into the intestine; in the second step, the chewing effect increased the polystyrene foam and The contact area between the microorganism and the extracellular enzyme, the ingested debris is further depolymerized into small molecule products under the action of extracellular enzymes secreted by the intestinal microflora; in the third step, these small molecule products are present in various enzyme and yellow larvae self enzymes In the process, the larvae are further degraded and assimilated to form the larvae's own tissue; the remaining foam fragments and partially degraded intermediates in the fourth step are mixed with part of the intestinal microbes and excreted in the form of worm feces. The foam in the insect feces may also be released. Continue further degradation.
"Tumblenose can digest the most difficult to degrade polystyrene plastics, and other relatively easily degradable plastics, theoretically, Tenebrio can also be digested." Professor Yang Jun told the Yangcheng Evening News reporter, he introduced that currently domestic manufacturers have considered using artificial Cultivate tenebrio or waxworms to degrade plastic waste.
However, he still called for responding to the increasingly serious white pollution, using less or banned disposable plastic products, and using more reusable products to be responsible for the future and future generations.
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