In conclusion, I. sakaiensis has been known to degrade PET to CO2 under aerobic condition, and we demonstrate here that it can also metabolize PET to acetate and ethanol under anaerobic conditions (30 °C, pH 7, 1 atm). This new plastic fermentation process by I. sakaiensis is supported by isotopic labelling studies and genome analysis, which revealed the presence of all the required proteins. The present results confirm that I. sakaiensis is a facultative anaerobe that shows versatile metabolic pathways for PET consumption and utilization under anaerobic and aerobic conditions. Plastic contaminated areas may have a lower oxygen level as plastic materials prevent oxygen penetration from the atmosphere, which could be a reason for the emergence of the observed anaerobic pathway for plastic degradation. This study identifies plastic fermentation as a novel approach to combat plastic pollution and produce high-value chemicals from waste through microbial degradation and biosynthesis. Additionally, the symbiotic association of I. sakaiensis with G. sulfurreducens paves a unique pathway to produce electricity from PET plastic waste. This work therefore reports a novel PET upcycling process,