The Impact of Oxygen on Mtr-expressing Escherichia coli

In bioelectrochemical systems (BESs), anaerobic conditions are used to generate current from microorganisms because oxygen can compete with an electrode as a terminal electron acceptor. However, prior studies have shown that oxygen enhances current production from <i>Shewanella oneidensis</i> MR-1 by counterbalancing a modest decrease in current per cell with a substantial increase in the total biomass. This opens the possibility that BESs based on oxygen-tolerant microorganisms might not need anaerobic conditions for maximal current production. Here we investigated this question in the facultative anaerobe <i>Escherichia coli</i>, which has been engineered to produce current using the Mtr pathway from <i>Shewanella oneidensis</i> MR-1.<br/>To investigate the effect of oxygen on the current production of <i>Escherichia coli</i>, we have introduced different oxygen levels to BESs containing Mtr-expressing <i>E. coli </i>and monitored current production, biomass, protein expression and metabolic products. Our results showed that oxygen exposure substantially boosted current up to 30-fold relative to anaerobic conditions. With increasing oxygen levels, both the current per cell and total biomass increase. Oxygen enhances the expression of the Mtr proteins relative to anaerobic conditions. Additionally, oxygen levels linearly increased the abundance of the first protein in the Mtr pathway, indicating that this protein is the limiting step in the current production. Additionally, oxygen increased energy flux and substrate utilization.<br/>In summary, oxygen enhances the current production of Mtr-expressing <i>Escherichia coli</i>. This work challenges the prevailing paradigm that anaerobic conditions promote current production, suggesting that bioelectronic applications can be performed in oxygen-rich conditions.