The larvae of the darkling beetle Tenebrio molitor, also known as mealworms, digest polystyrene (PS) exceptionally quickly with the aid of their gut microbiome. By studying this natural biodegradation process, we aim to develop biotechnology for sustainable PS waste transformation. A key step is to determine which microbes are responsible for PS biodegradation; however, few PS-biodegrading microbes have been reproducibly cultivated from mealworm guts, limiting our ability to investigate the underlying mechanisms. Furthermore, previous studies disagree as to whether the mealworm microbiome changes in response to a PS diet. These studies have pooled mealworm guts, likely obscuring variations among individual mealworms. To address this gap and inform cultivation efforts, we conducted a full factorial experiment to assess how the gut microbiomes of individual mealworms respond to different diets (PS, bran, PS+bran, and starvation). Over five weeks, we monitored the gut bacterial composition of individual mealworms using 16S rRNA-based community profiling, hypothesizing that PS-fed mealworms would be enriched in PS-biodegrading microbes. Gut bacterial composition varied among individual mealworms; however, by week 5, the gut bacterial compositions clustered by diet, with PS-fed mealworms showing the highest similarity to each other. PS-fed mealworms were enriched in Enterobacteriaceae while bran-fed mealworms were enriched in Clostridiaceae. This experiment confirmed that i) mealworm microbiomes exhibit individuality, ii) mealworm microbiomes converge to shared community composition in response to a PS diet, and iii) PS- and bran-based diets enrich for different microbial communities, informing us of which taxa may contribute to PS biodegradation. PS depolymerization was confirmed using gel permeation chromatography, by comparing the molecular weight of feedstock PS to that of egested PS. These results are guiding the design of media to isolate and study candidate PS-degrading microbes. This work advances our understanding of natural microbial plastic biodegradation and supports the development of biotechnology for managing plastic waste at the end of its lifecycle.
