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                  What is biology explanation?
                  Release time:2021-12-01 16:43:32      Hit count:79

                  "The rapid biodegradation of plastic in the mealworm's gut reveals a new fate for plastic waste discarded in the environment." Beijing University of Aeronautics and Astronautics Professor Yang Jun said.

                  Plastics are difficult to degrade naturally in the environment, and polystyrene is the most of them. Because of its high molecular weight and high stability, it is generally believed that microorganisms cannot degrade polystyrene plastics. In 2015, professor Yang jun's research group from beihang university and Dr. Zhao jiao from shenzhen bgi jointly published two sister research papers on EnvironmentalScience&Technology, an authoritative journal in the field of environmental science. Proved that the larvae of mealworm (mealworm) can degrade polystyrene, the most difficult plastics to degrade.

                  In this study, the larvae of mealworm can survive for more than one month on polystyrene foam as the sole feeding source, and finally develop into adults. The polystyrene they eat is completely degraded and mineralized into CO2 or assimilated into body fat. The findings provide insights into how to tackle the global problem of plastic pollution.

                  The world's problems

                  The pollution of plastic waste produced by petrochemical industry is a global environmental problem. Most plastic is thrown away after use for single-use consumption. So far, the academic community believes that plastic products may not be decomposed for tens to hundreds of years in the natural environment because of their stable physical and chemical structures.

                  Professor Yang jun introduced that in 2013, the world consumed 299 million tons of plastic, of which polystyrene accounted for 7%, consumption of about 21 million tons a year, common plastic lunch boxes, coffee cups and other materials that can withstand the temperature of boiling water is polystyrene. Authoritative investigations have shown that polystyrene degrades within the microbial community of soil, sludge, rotting garbage, or manure in the range of 0.01% to 3% in four months.

                  Every year 40 million tons of waste plastic accumulates in the environment around the world, and about 2 million tons of waste plastic is thrown into the environment in China every year. Take agricultural film as an example, the annual output of agricultural film in China reaches one million tons, and increases by 10% annually. No matter what kind of crops are covered, all the soil covered with film has residual film. According to statistics, the annual residue of agricultural film in China is as high as 350,000 tons, the residual film rate of 42%, a large number of residual film left in the farmland 0-30 cm tillage layer. That is to say, nearly half of the agricultural film remains in the soil, which is a great hidden danger for food safety.

                  "It can take 200-400 years for plastics to be completely assimilated by microorganisms in the soil and degraded to CO2 and water for inorganic mineralization, resulting in accumulation in the environment." Professor Yang Jun told the Reporter of Yangcheng Evening News.

                  Insects help

                  Since 2005, Yang's team has been studying plastic biodegradation. Focus on the most difficult to degrade polystyrene and other plastic degradation.

                  Scientists have experimented with several soil invertebrates, such as earthworms, millipedes, slugs and snails, to see if they can eat plastic. When fed 14C labeled plastics such as polyvinyl chloride (PVC), polyethylene (PE) and polypropylene (PP), the results showed that they were not degradable.

                  Yang jun believes that the idea of biodegradable plastics should not be limited to microorganisms. We can consider lepidopteran insects, termites and other Marine boaters that can erode polyethylene and submarine cables. We can also consider the isolation and cloning of key enzymes and genes that can produce active groups from these organisms.

                  A 2014 study by Yang's team found that wax worms (caterpillars of the Indian Caterpillar) can chew and eat polyethylene PE film, and two strains of enterobacter YT1 and Bacillus YP1 that can degrade PE film were isolated from the intestines of the caterpillars. The team then discovered that the mealworm larvae, a more plastic-eating animal, are larger than the wax worms (typically 35 mm long and 3 mm wide) and can eat only styrofoam. The yellow mealworm has four life stages: egg, larva, pupa and adult.

                  Mealworms, also called mealworms, belong to coleoptera, tenebridae, tenebridae (Tenebridae) in insect taxonomy. Native to North America, the mealworm was introduced from the former Soviet Union to China in the 1950s and is known as "protein feed bank". Its dry goods contain fat 30%, contain protein up to 50% above, in addition also contain phosphorus, potassium, iron and other elements. Dried mealworms contain 40% protein in larvae, 57% in pupae and 60% in adults.

                  In China, yellow mealworms are actually similar to silkworms. They can be eaten directly, fried, or used as fodder. Scorpions, centipedes, gecko, snakes, tropical fish and goldfish fed with yellow mealworms not only grow fast, have a high survival rate, but also have strong disease resistance and greatly improve their fertility. Mealworm farming is very easy, farmers can use fresh oats, wheat bran, apple farming.

                  Bugs eat plastic

                  Professor Yang jun's team bought polystyrene plastic materials from Sinopec's Yanshan branch, which contained no additives or catalysts. Alpha-13c and β-13C labeled polystyrene samples were purchased from the United States. Yellow mealworms are bought from insect farms in Daxing, Beijing and Qinhuangdao, Hebei province, and raised on grain. These insects are three to four years old (that is, they molt three to four times).

                  The mealworms were placed in a polypropylene plastic container with styrofoam blocks. The weight of the foam blocks eaten by mealworms was measured periodically. The control group was fed with conventional wheat bran. 500 mealworms were fed with 5.8g of foam as the only food, and were raised alone in a controlled greenhouse (25±1°C, 80±2% humidity, and 16:8 light/dark cycle). Dead mealworms are removed immediately during incubation.

                  Yang Jun et al. fed mealworm larvae with foamed plastic as a single food source. Compared with normal (bran fed) and non-fed larvae, it was found that the dry weight of the larvae increased by only 0.2% (due to the lower water content and nutritional value of the foam compared to bran) over the 16-day period, although it did not increase as significantly as normal (+33.6%). There was no significant decrease in dry weight (-24.9%), and no significant difference in survival between the plastic and bran groups.

                  One hundred mealworms can consume 34-39 milligrams of styrofoam per day. During the 16-day trial period, 47.7% of the foam consumed by the worms was converted to CO2. The residue (49.2%) is converted into biodegradable particles similar to rabbit feces and excreted out of the body. Tests using α-13C or β-13C labeled polystyrene plastics confirmed that they were mineralized to carbon 13 labeled carbon dioxide and lipids. The polystyrene foam in the larval intestine degrades within 24 hours.

                  The larvae fed styrofoam as their only diet developed into adult crustaceans as healthy as those fed normal food (wheat bran) for a month. Mealworms eat holes in the foam. After passing through the bugs' guts, the chemical structure and composition of the foam ingested changes. By using gel permeation chromatography (GPC), carbon 13 nuclear magnetic resonance spectroscopy, and thermal Fourier transform infrared spectroscopy, it was confirmed that the long-chain polystyrene molecules in the larval intestine were broken to form insect metabolites excreted with feces.

                  In addition, Exiguobacteriumsp.YT2, a polystyrogen-degrading bacterium, was successfully isolated from the intestinal tract of larvae. The strain has been preserved in the General Microbiology Center and national Gene Bank of China, and it is the first polystyrogen-degrading bacterium reported in the world.

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