We noticed that during EG metabolism, ethanol was further degraded into acetate when EG was almost consumed (Figure ). To investigate the possibility of ethanol conversion, we cultured I. sakaiensis directly with 13 C labelled ethanol and H and 13 C NMR spectroscopy showed indeed the gradual fermentation of ethanol to acetate (Figure ). Based on this observation, we propose that the initially produced ethanol during EG and PET fermentation can reenter the cell, followed by conversion to acetaldehyde by ADH and further fermentation to acetate (Figure ). Maltose fermentation: It has previously been shown that I. sakaiensis can neither grow aerobically on glucose nor ferment it. The lack of transporters for glucose was found to prevent I. sakaiensis from glucose uptake . However, aerobic growth with maltose has been verified previously . Our genome search suggested the possibility of maltose fermentation by I. sakaiensis (Table ) and fermentative growth of I. sakaiensis was therefore also studied with maltose (40 mM) as the sole carbon source under anaerobic condition. We detected the following fermentation products by 1 H NMR spectroscopy: lactate, formate, acetate, and ethanol (Figure ). Under aerobic condition, maltose is oxidized to CO2 and H2O through the TCA cycle (Figure ). Under anaerobic conditions, maltose is fermented to a product pool via a protein network starting from the outer membrane to the cytoplasm in I. sakaiensis (Figure ) . All the necessary proteins are available in the genome of I. sakaiensis with the exception of pyruvate formate lyase (PFL), which has yet to be identified (Table ) .