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Web Date: September 30, 2015

Mealworms Munch Polystyrene Foam

Plastics: Bacteria in the guts of the worms digest stubborn polystyrene
Department: Science & Technology | Collection: Life Sciences
News Channels: Environmental SCENE, Biological SCENE, Materials SCENE
Keywords: mealworms, plastic, biodegradable, polystyrene foam, Styrofoam, bacteria
Mealworms chow down on expanded polystyrene foam and can convert almost half of what they eat into carbon dioxide.
Credit: Environ. Sci. Technol.
Photo of mealworms eating holes in polystyrene foam.
Mealworms chow down on expanded polystyrene foam and can convert almost half of what they eat into carbon dioxide.
Credit: Environ. Sci. Technol.
Bacteria inside the mealworm gut can degrade the recalcitrant plastic polystyrene.
Credit: Environ. Sci. Technol.
Scanning electron micrograph of bacteria inside the mealworm gut.
Bacteria inside the mealworm gut can degrade the recalcitrant plastic polystyrene.
Credit: Environ. Sci. Technol.

Polystyrene—most familiarly produced as foams, including Styrofoam—has given the world cheap, lightweight insulation and containers for taking food to go. But the material biodegrades so slowly that it can sit in a landfill for hundreds of years. A new finding points to a potential solution: Mealworms will dine on polystyrene foam when they can’t get a better meal, converting up to 48% of what they eat into carbon dioxide (Environ. Sci. Technol. 2015, DOI: 10.1021/acs.est.5b02661).

To stem the tide of plastic waste, researchers have been searching for microbes or invertebrates that can biodegrade hydrocarbon-based polymers into inorganic compounds such as CO2 and water. In an effort to find creatures that might digest stubborn polystyrene, Jun Yang and Lei Jiang of Beihang University, in Beijing, along with their colleagues, tested mealworms—the tan, segmented larvae of the mealworm beetle. Mealworms are raised for pet food, and have even been proposed as a dietary protein supplement for people.

The larvae will eat polystyrene, the team found, though perhaps understandably, they prefer not to. “When we supply additional food like potatoes, mealworms will eat potatoes first,” Yang says. To see if the worms were biodegrading the plastic, the team set up three incubators: sealed glass jars each holding 40 worms and a 6 g block of polystyrene foam. The team then monitored the CO2 the mealworms produced. After 16 days, the researchers quantified the carbon in the remaining polystyrene, the mealworms, and the critters’ fecal matter using elemental analysis; they also analyzed the compounds in the worms’ feces with nuclear magnetic resonance.

The mealworms ate about a quarter of the foam, converting some of it to CO2 at a rate that increased throughout the experiment. At 16 days, they had converted 48% of the carbon they had eaten into CO2 and excreted 49% in their feces. Only 0.5% was incorporated into the worms’ bodies—comparable to the small amount of carbon termites absorb when eating wood. The compounds in the mealworms’ fecal matter had 20% lower molecular weight on average than the original polymers, indicating the polystyrene was degraded in their guts.

Yang and his team also showed that microbes in the mealworms’ guts were responsible for breaking down the polystyrene. When they gave the worms the antibiotic gentamicin, the polystyrene in their fecal matter no longer showed degradation (Environ. Sci. Technol. 2015, DOI: 10.1021/acs.est.5b02663).

To zero in on these polystyrene-splitting microbes, the team then isolated 13 bacterial cultures from the guts of the mealworms and grew them on polystyrene film. The most abundant was a strain of Exiguobacterium. Over two months, the bacteria made holes and cavities in the film, although the degradation was less efficient than in the mealworms’ guts.

Ramani Narayan, an expert in plastic biodegradation at Michigan State University, says the researchers have made an interesting discovery, but that it is not yet ready for practical application. He notes that about half of the polystyrene the mealworms eat is excreted back into the environment in fragments that may not be biodegradable and could carry toxins up the food chain.

Yang agrees that applying the discovery to manage waste—perhaps by engineering bacteria that could boost the reported biodegradation—may take time. Next, he and his colleagues hope to understand the mechanism and environmental factors responsible for degradation in the mealworms’ guts, and identify the bacterial enzymes and genes involved.

Chemical & Engineering News
ISSN 0009-2347
Copyright © American Chemical Society
@passivelogical (October 1, 2015 2:26 AM)
Why digest it when you can infinitely recycle expanded polystyrene - "Cradle to Cradle" in the technological cycle? Feed the mealworms on waste cellulose which makes soil and you get a "Cradle to Cradle" loop in the biological cycle. The two cycles can be separate so long as they are each closed. Expanded polystyrene is a renewable resource, ignorance makes us regard it as waste.
David (October 8, 2015 1:35 PM)
Recycling expanded polystyrene sounds good but it is not nearly as sustainable as you have made it sound. There is a high energy cost in recycling it, both in transportation and processing, largely due to the material's low density.
Deirdre Lockwood (October 8, 2015 3:50 PM)
Thanks for your comments! For more on the cost of recycling expanded polystyrene, check out this video in the Speaking of Chemistry series.
Jack (October 11, 2015 10:59 PM)
If @passivelogical is correct in stating that expanded polystyrene is a renewable resource, and that expanded polystyrene can be infinitely recyclable, then the cost of recycling it should be considered an ecological priority. Degrading it by 48% "which sounds to me like more than half is still polluting waste) seems to me vastly inferior to recycling 100%, from an environmental perspective.
That said, David says that the energy cost of recycling is high, and indicates that is therefore economically unfeasible. Expanded polystyrene can be reshaped extremely easily, and the lack of density would cheapen, not multiply its' transportation cost.
CS (February 26, 2016 3:53 PM)
"Expanded polystyrene can be reshaped extremely easily, and the lack of density would cheapen, not multiply its' transportation cost."

This is not exactly true. Freight companies really don't care how much the load weighs as long as it isn't over weight. If you are shipping a load of EPS domestically and it weighs 3K pounds as opposed to 44K pounds of a more dense recyclable, the freight has to be tacked onto the price per pound of the material. $1000.00 in freight (no matter the weight on the trailer as long as not over weight) would add $.33 per pound to the cost of the EPS while a heavier recyclable would only realize an additional $.023 per pound.

This is largely why a niche market of in house densifying equipment has been developed.

The light load is only a benefits the trucking companies but they do not rebate the savings, at least they've never provided me one.

hsfrey (October 1, 2015 6:38 PM)
Were the worms able to grow and develop normally on an all polystyrene diet?

If not, what additional nutrients were required?
Deirdre Lockwood (October 5, 2015 10:39 AM)
Thanks for your comment. Yes, they grew and developed normally into beetles, and had the same survival rate as mealworms fed on a diet of bran.
John Lentini (October 7, 2015 2:12 PM)
Who remembers Mutant 59? Plastic eating bacteria destroy civilization!
Brian J. B. Wood (October 8, 2015 5:21 AM)
As a microbiologist I am inclined to think that pure cultures comprising a single bacterial species will probably be less effective at biodegradation than a consortium, with different species performing different tasks, and this is supported by the observation that pure cultures were less effective than the consortium in the mealworm gut. The latter environment may also provide ancillary nutrients that benefit bacterial growth and the capacity to utilize xenobiotics.
Tom (October 11, 2015 5:03 PM)
Why not give it an afterlife use and completely eliminate expanded polystyrene going to landfill? Styromelt is the answer. It has a compaction rate of up to 95%. The machine heats the styrofoam down to a liquid and forms it into a briquette. This briquette is then collected by recyclers and processed back into other products such as picture frames etc. It basically reverses the manufacturing process.
Due to the machine being a hybrid and using thermal compaction, the styrofoam is also sterilised; the machine can reach temperatures of up to 300 degrees Celsius. Therefore, products such as fish boxes can be fully recycled using this technology.
For more information, visit our website:
Ewan Martin Quirk  (November 17, 2015 1:43 AM)
Leaving styrofoam in the food waste stream is the obvious low energy cost solution.
Joelle clermont (January 15, 2016 1:07 PM)
I just started breeding mealworm for future human consomption. Where can I find this complet research? I want to know what is the chemical equation link to the degradation by the bacteria, and what are the by products left in the mealworm and its dropping. Could it be safe to eat by any other predator? Bird, reptiles or I mean, raising insects are the source of protein of the future, if at the same time you get ride of some plastic we create, this is a HUGE thing, making the wheel of ecology turn again!
Andrey Mantula (June 28, 2017 10:10 AM)
During the year, I observe how sea worms (polychaetes) eat polisternen in my pontoons in the marina.
In two pontoons for buoyancy 30 cubic meters of polystyrene. This is a good feed base for worms. During the year, worms ate about 30% of polystyrene.
I'm not a microbiologist, but the usual harbor master of a yacht marina in Cambodia. Port of Sihanoukville, the Gulf of Thailand.
To whom it is interesting from scientists write to me on e-mail. There are photos and video of the process. The Nobel Prize is possible :)
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