Mealworms: From Farm Pests to Conservationists

Ankith Rao
Thomas Jefferson High School for Science and Technology

“They’re here!” our Biotechnology Lab mentor exclaims. We’d been waiting for the test subjects for a few weeks, doing training labs in the meantime. Donning our lab coats and gloves, we extracted the subjects from the fridge. They slithered around in the cold grain, dodging in and out of sight. I picked up a fat one, it coiling and writhing between the forceps. I attempted to keep it still, let alone extract the intestinal tract under a microscope. My lab-mate struggled with dissecting his mealworms as well, feeling nauseous every second of the process. The crunch of the exoskeleton as you slice off its head didn’t help, either. The fibrous, brown gut slid cleanly out from the rest of the tissue. No wonder farmers hate these things, I tell myself, hoping our research on the plastic-eating creatures isn’t for naught.

Although the larva of Tenebrio molitor are known for being farm pests that destroy grains (hence their colloquial name, the mealworm), these creatures are important to us because of something else they eat: plastics. Because of Styrofoam’s extremely stable chemical composition, most multi-cellular organisms and bacteria cannot break it down into its basic components. However, the mealworm can achieve this monumental task, at the relatively quick rate of 35 mg per day [7]. The goal of this project is to determine exactly which bacteria inside the mealworm’s gut allow it to break plastics, namely Styrofoam, into biodegradable products. By feeding the worms plastic, the relative number of plastic-degrading bacteria in the mealworm gut increases. Measuring this relative increase with 16S rRNA analysis allows us to directly determine which bacteria contribute to the worm’s amazing ability. The utilization of the 16S rRNA sequence is key to pinpointing the bacteria responsible for plastic-degradation in the mealworm. This sequence in the bacterial genome serves as a “fingerprint” for all bacteria, since each 16S region is unique to a bacterial species. From metagenomic analysis of this region, researchers can determine which bacteria are which with relative ease. 16S analysis of the bacteria that increased in relative abundance after feeding the mealworms plastic allows us to immediately see which bacteria contribute to the mealworm being able to degrade plastic. Not much research has been done in this field previously, since the combination of mealworm microbiology with environmental conservation is niche to say the least.

The earliest publication on plastic-degrading bacteria in mealworms came from Yang et. al., a group of Stanford researchers that found that mealworms could survive on a diet of just Styrofoam [6]. Their original research dealt with the similarly plastic-degrading waxworms, but mealworms proved to be a cheaper and simpler alternative [6]. The group isolated a bacterial strain from the mealworm, Exiguobacterium strain YT2. Our project seeks to use new methods to examine a wider range of bacteria without the limitations of Yang et. al.’s method. We will sequence the bacteria after a simple preparation and purification instead of taking the intermediate step of culturing the bacteria. Culturing not only requires knowledge of the specific set of chemicals that the bacteria need to survive, many of which we don’t know or don’t have access to, but also doesn’t help us since we don’t know exactly which bacteria we are looking for. We are also not giving the worms antibiotics, which Yang et. al. did to help culture their target bacteria.

A Stanford blog wrote about Yang et. al. shortly after the publication of their paper [3]. The post explains that Yang and his team are continuing to flesh out research on the topic, testing if other plastics can be degraded and if there are aquatic counterparts to the mealworm. As other media sources brought this research to light, including CNN [2], Yang’s research has broadened to ecological impact as well, testing the effects of plastic-degradation down the mealworm food chain. Research like this helps prevent unwanted aftereffects of seemingly harmless technological advances, letting science take one step forward instead of two steps back.

Jeffery Shultz, an expert in insect anatomy from the University of Maryland, guided us in the early stages of our project. He not only directed us on how to dissect the mealworms, but gave us valuable resources on care, upkeep, and disposal of the worms (J. W. Shultz, personal communication, December 12, 2016). Shultz’s advice has helped our project’s efficiency increase greatly, despite his lack of conservational experience. Another group has since expanded on the research that Yang et. al. has conducted. Duhaime, Osborn, and Oberbeckmann have researched how microbes adapt to marine environments in the context of plastic-degradation. The group found that as the season changes, different types of bacteria tend to colonize on plastic debris in the ocean. Duhaime et. al.’s research exposes the plethora of bacteria we could be looking for in our research, as well as the larger purpose of our project.

As I stared at the contorting worm between my tweezers, my mind wandered into future research on our project. The plastic-degrading bacteria could be isolated and genetically modified to increase efficiency and survivability in various environments and climates. Even the enzymes used to break down the plastic could be harnessed for use outside the bacteria itself. Plastic waste all over the world could be reduced to nothing and turned into biodegradable matter instead of burned or left alone for millions of years to come, all because of one little farm pest.

References

[1] Eriksen, M., Lebreton, L. C. M., Carson, H. S., Thiel, M., Moore, C. J., Borerro, J. C., Reisser, J. (2014). Plastic pollution in the world’s oceans: More than 5 trillion plastic pieces weighing over 250,000 tons afloat at sea. PLOS One. http://dx.doi.org/10.1371/journal.pone.0111913

[2] Imam, J. (2016, July 21). Styrofoam-eating mealworms might help reduce plastic waste, study finds [Newsgroup post]. Retrieved from http://www.cnn.com/2015/09/30/us/styrofoam-eating-mealworms-plastic-waste/

[3] Jordan, R. (2015, September 29). Plastic-eating worms may offer solution to mounting waste, Stanford researchers discover. Retrieved January 19, 2017, from http://news.stanford.edu/pr/2015/pr-worms-digest-plastics-092915.html

[4] Oberbeckmann, S., Osborn, A. M., & Duhaime, M. B. (2016). Microbes on a bottle: Substrate, season and geography influence community composition of microbes colonizing marine plastic debris. PLOS One. http://dx.doi.org/10.1371/journal.pone.0159289

[5] Yang, J., Yang, Y., Wu, W.-M., Zhao, J., & Jiang, L. (2014). Evidence of polyethylene biodegradation by bacterial strains from the guts of plastic-eating waxworms. American Chemical Society. http://dx.doi.org/10.1021/es504038a

[6] Yang, J., Yang, Y., Wu, W.-M., Zhao, J., Jiang, L., Song, Y., Yang, R. (2015a). Biodegradation and mineralization of polystyrene by plastic-eating mealworms: Part 1. chemical and physical characterization and isotopic tests. American Chemical Society. http://dx.doi.org/10.1021/acs.est.5b02661

[7] Yang, J., Yang, Y., Wu, W.-M., Zhao, J., Jiang, L., Song, Y., Yang, R. (2015b). Biodegradation and mineralization of polystyrene by plastic-eating mealworms: Part 2. role of gut microorganisms. American Chemical Society. http://dx.doi.org/10.1021/acs.est.5b02663