Potential biodegradation of plastics through probiotic microbial consortia inoculated during vermicomposting (Eisenia fetida) of microplastic-spiked biowaste

The use of organic amendments (compost or fresh waste) contaminated with microplastic (MP) negatively impact agricultural soil quality. This study aimed to evaluate a novel biotechnological process to enhance the efficiency of plastics degradation. Two distinct microbial consortia were utilized: Endogenous-Plastic Microbial Consortia (ENDO-PMC), isolated from the gut microbiome of earthworms previously exposed to low-density Polyethylene (LDPE) and tested as probiotics for E. fetida ., and the Exogenous-PMC (EXO-PMC), composed by lignolytic microorganisms isolated from compost and selected for their plastic-degrading enzymatic activity. Then, both consortia were tested during vermicomposting of microplastic-spiked biowaste (1.25%) in mesocosm-scale trials using LDPE and a mixed plastic blend (LDPE+LLDPE+PS + PET). Earthworm survival and weight variation were monitored, along with key enzymatic biomarkers related to oxidative stress. Selective culture media and 16S rRNA amplification techniques were used to assess the presence of the inoculated microbes in the vermicompost and in the intestinal tract of E. fetida . Plastic degradation efficiency was evaluated using thermogravimetric analysis coupled with mass spectrometry (TGA-MS). The results showed that probiotic-inoculated earthworms exhibited an improved survival rate under plastic waste exposure. Additionally, a reduction in the oxidative stress response was observed in these earthworms. TGA-MS analysis revealed a low LDPE biodegradation rate at the end of the bioassay, although this technique showed certain limitations as a useful tool for evaluating the biodegradation process. These findings underscore the potential of probiotic inoculation for improve the earthworm's resilience to the exposure to plastics. However, further optimization of the assembly of microbial consortia to enhance the biodegradation rate, and especially a more accurate plastic detection technique, are needed to improve this biotechnological approach. • The probiotic potential of earthworm microbiota exposed to plastics was evaluated. • Molecular techniques (16S rRNA) tools tracked probiotic persistence in gut and vermicompost. • Probiotic earthworms exhibited a higher survival rate under plastic stress. • Biomarker analysis showed reduced oxidative stress and neurotoxicity with probiotics. • The TGA-MS technique is not suitable for providing clear information on the biodegradation process of these plastics.