Denitrification and aerobic respiration, hybrid electron transport chains and co-evolution

► The bioenergetics and potential co-evolution of denitrification and aerobic respiration are explored. ► The advantages and disadvantages of combining the two pathways in a single, hybrid respiratory chain are discussed. ► The experiment evidence for co-respiration of nitrate and oxygen is critically reviewed. ► A scenario for the co-evolution of the two pathways is presented.