Evidence of polystyrene biodegradation by gut microbiota of Styrofoam-feeding yellow mealworms (larvae of Tenebrio molitor Linnaeus)

Abstract:

[Background] Plastic are synthetic polymers derived from fossil oil and largely resistant to degradation. Plastic litter have adverse effects on the environment and marine biota. Therefore, new solutions for petroleum-based plastic waste degradation are urgently needed. [Objective] Polystyrene (PS) is notoriously persistent plastic that is not degradable at appreciable rates for decades. However, an environment was identified in which PS is susceptible to biodegradation: yellow mealworm, the larvae of Tenebrio molitor Linnaeus, can damage PS packing by chewing and eating styrofoam. So we try to isolate PS-degrading microorganisms from the mealworms’ gut. [Methods] The larvae fed with styrofoam as the sole diet could live as well as those fed with bran diet over several months. Based on morphological, physiological and biochemical properties as well as 16S rRNA gene and ITS gene sequences analysis, the phylogenic tree was constructed to identify the taxonomic status of the strains. [Results] Two bacterial strains capable of degrading styrofoam were isolated from worm fecula egested from styrofoam-feeding larvae, named as Bacillus anthracis PSI-1 and Enterobacter hormaechei PSI-2. A PS-degrading fungal strain was isolated from the gut of mealworms and identified as Aspergillus niger KHJ-1. Over a 14-day incubation period of the fungal train KHJ-1 on PS films, a large number of cavities were obviously observed on PS films surfaces, and the changes were measured about the film of mechanical properties. The results showed that hydrophobicity of the film was decreased dramatically, the elongation at break and the tensile strength became smaller. A suspension culture of KHJ-1 strain was able to degrade 214.8 mg/5 g of PS solid particles, the weight loss ratio of PS was 4.29% over a 60-day incubation period. [Conclusion] The results demonstrated the presence of PS-degrading bacteria and fungus in the guts of mealworms could degrade PS directly and efficiently and provided promising evidence for the biodegradation of PS in the environment.