Increase of riboflavin biosynthesis underlies enhancement of extracellular electron transfer of Shewanella in alkaline microbial fuel cells

► Shewanella delivers the highest power output at pH = 9. ► Shewanella synthesizes 0.6 times higher level of riboflavin at pH = 9 than 7. ► Increased riboflavin synthesis underlies enhanced electron transfer in Shewanella.