Biodegradation of foam plastics by Zophobas atratus larvae (Coleoptera: Tenebrionidae) associated with changes of gut digestive enzymes activities and microbiome

In order to uncover the plastic types that superworm Zophobas atratus can degrade and the underlying changes associated with plastics consumption, three types of plastics including polystyrene (PS), polyethylene (PE) and polyurethane (PU) foam were used as sole feedstock to feed the superworm larvae for 35 days with bran as control. Compared to the control, PS- or PU-fed larvae showed 100% survival rates, the PE-fed and starvation larvae had decreased survival rates of 81.67% and 65%, respectively. Both plastics-fed and starvation groups showed decreased larvae weight. The consumption rates of PS, PE, and PU were 1.41, 0.30, and 0.74 mg/d/larva, respectively. The attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and differential scanning calorimeter and thermogravimetric (DSC-TGA) analyses demonstrated the changes of functional groups and thermostability in frass compared to plastic feedstocks, indicating the partial oxidation and degradation of plastics. Among the gut digestive enzymes tested, protease showed increased activities in all plastics-fed groups. Gut microbial communities displayed significant relative abundance changes such as increased abundances of Enterococcus in all plastic-fed groups, Citrobacter in PE-fed group, Dysgonomonas and Sphingobacterium in PS-fed group, and Mangrovibacter in PU-fed group. The latter 3 genera were reported for the first time. In summary, the results demonstrated that Z. atratus could efficiently degrade both PS and PU foam plastics, and the plastic degradation was associated with changes of gut microbial communities and digestive enzyme activities.