PET and EG fermentation by I. sakaiensis: I. sakaiensis is a gram-negative, rod-shaped bacterium with a cream color (Figure ) after incubation in the culture medium (NBRC no. 802, Table ) under aerobic conditions for 24 h. I. sakaiensis is so far considered as an aerobe and was originally isolated from sediments nearby a plastic recycling plant . Sediments can show frequent shifts between aerobic and anaerobic states . Therefore, microbial communities in sediments often show a facultative trait, which means that they can survive in more than one specific condition and do not only show aerobic respiration but also have the ability to ferment and utilize hydrogen. This is often indicated by a rich abundance of fermenting and hydrogenase enzymes in the genome . Fermentation usually yields acids and hydrogenases keep the redox balance in fermenting bacteria by regulating the proton-hydrogen equilibrium . Therefore, the ability to metabolize hydrogen is frequently observed in anaerobes . Specifically, the genome of I. sakaiensis shows the presence of [NiFe] hydrogenases and many fermenting enzymes such as carbon monoxide dehydrogenases, lactate dehydrogenases, alcohol dehydrogenases, acetate kinase among others (Table ). Additionally, genes predicted to code for proteins involved in the anaerobic metabolism such as iron-sulfur proteins, cytochrome c family proteins, nitrate reductase, nitrite reductase, sulfite reductase, and dimethyl sulfoxide reductases are present in the genome of I. sakaiensis as well as anaerobic regulatory proteins CRP/FNR family transcriptional regulator and ferric uptake regulator protein (Fur) (Table ). The gene analysis therefore reveals a richness of fermenting and anaerobic enzymes in the genome of I. sakaiensis, which inspired us to investigate its fermentative metabolism.