Different performances in polyethylene or polystyrene plastics long-term feeding and biodegradation by Zophobas atratus and Tenebrio molitor larvae, and core gut bacterial- and fungal-microbiome responses

The biodegradation of plastics by insect larvae is considered as an emerging strategy for the resistant plastic wastes disposal. To uncover the correlation of insect larval gut-microbiome with plastics biodegradation, two worm species including superworm Zophobas atratus and yellow mealworm Tenebrio molitor were fed with either polyethylene (PE) or polystyrene (PS) foam as sole diet for a longer period of 45 days, sole bran diet was used as control. Rapid declines of survival rates and plastic ingestions after 30 days were observed, suggesting that longterm sole plastic diet was detrimental to growth and life cycle completion in both larval species. Both PE and PS plastics were found more extensively depolymerized and biodegraded in gut of yellow mealworms than that of superworms by GPC analysis. The larval gut bacterial- and fungal-microbiomes at day 45 were assessed by Illumina MiSeq. The results showed that both gut bacterial and fungal communities shifted upon sole plastic diet ingestion compared to the control. Gut bacterial communities were similar in PS-fed groups but significantly different in PE-fed groups between both species. In contrast, gut fungal communities were clustered by species in general, although they were similar between PE- and PS-fed yellow mealworms but were more divergent beotween PS- and PE-fed superworms. Analysis of the changes of relative abundances of dominant bacterial and fungal genera demonstrated the strong association between the distinctive gut microbiome and plastic degraodation. For instance, Spiroplasma and Rhodotorula for PE degradation, Cryptococcus for PS degradation in mealworms. Issatchenkia for both PS and PE degradation, Pseudomonas for PS degradation in superworms. In conclusion, changes of both gut bacterial- and fungal-microbiomes diversities were associated with plastic feedstock types and larval species, especially fungal microbiomes were strongly associated with larval species.

Automated summary

Long-term sole plastic diet has detrimental effects on the growth and life cycle of insect larvae. The gut of yellow mealworms is more suitable for the degradation of both PE and PS plastics, while the gut of superworms is more suitable for the degradation of PE plastics. There is a strong association between the gut microbiome and plastic degradation, especially for fungal microbiomes which are closely associated with larval species.