Extracellular electron transfer pathways to enhance the electroactivity of modified Escherichia coli

Escherichia coli (E. coli) show limited extracellular electron transfer (EET) that compromises their use in bioelectronics. We enhance the EET in E. coli by expressing an electron transfer pathway that spans the inner and outer membranes of the cell, including the periplasmic space in between. We observe a 54% enhancement in electron transfer for engineered E. coli expressing the endogenous inner-membrane NapC and periplasmic NapB cytochromes under non-native conditions with the outer-membrane MtrCAB complex from Shewanella oneidensis (S. oneidensis). The greatest enhancement, however, is observed for E. coli expressing the complete S. oneidensis Mtr pathway consisting of the inner-membrane CymA, periplasmic small tetraheme cytochrome (STC), and outer-membrane Mtr complex. This engineered strain shows a 3-fold increase in current generation compared with the empty vector control and a 2-fold increase compared with the state-of-the-art bioengineered strain comprising only the Mtr complex and CymA. These results highlight the importance of periplasmic shuttles in engineering EET.