Biodegradation and mineralization of polystyrene by plastic-eating superworms Zophobas atratus

Abstract

Polystyrene (PS) is one of the major plastic debris accumulated in environment. Previously, we reported that mealworm (Tenebrio molitor) was capable of degrading and mineralizing Styrofoam (PS foam). This finding arouses our curiosity to explore whether more other insect species have the same capability as mealworms. Here, an insect larva, superworm (Zophobas atratus), was newly proven to be capable of eating, degrading and mineralizing PS. Superworms could live with Styrofoam as sole diet as well as those fed with a normal diet (bran) over a 28-day period. The average consumption rate of Styrofoam for each superworm was estimated at 0.58 mg/d that was 4 times more than that of mealworm. Analyses of frass, using gel permeation chromatography (GPC), solid-state ¹³C cross-polarization/magic angle spinning nuclear magnetic resonance (CP/MAS NMR) spectroscopy, and thermogravimetric interfaced with Fourier transform infrared (TG-FTIR) spectroscopy, demonstrated that the depolymerization of long-chain PS molecules and the formation of low molecular-weight products occurred in the larval gut. A respirometry test showed that up to 36.7% of the ingested Styrofoam carbon was converted into CO₂ during a 16-day test period. The PS-degrading capability of superworm was inhibited by the antibiotic suppression of gut microbiota, indicating that gut microbiota contributed to PS degradation. This new finding extends the PS-degrading insects beyond the species within the Tenebrio genus and indicates that the gut microbiota of superworm would be a novel bioresource for pursuit of plastic-degrading enzymes.

Keywords: Biodegradation; Plastic waste; Polystyrene; Superworm; Zophobas.