Nanoscale Secondary Ion Mass Spectrometry Analysis of Individual Bacterial Cells Reveals Feedback from Extracellular Electron Transport to Upstream Reactions

We analyzed the metabolic activity of Shewanella oneidensis MR-1 respiring on an indium tin-doped oxide electrode with nanoscale secondary ion mass spectrometry (NanoSIMS) for quantification of the anabolism of 15N-labeled NH4Cl. Although acceleration of extracellular electron transfer (EET) did not enhance the average metabolic activity, the distribution of 15N intake among individual cells was drastically bipolarized upon EET rate enhancement, suggesting not only positive but also negative effects on cellular activity. The present data highlight the importance of controlling the downregulation of metabolic activity caused by the rate acceleration of EET to improve the efficiency of microbial electrode catalysis.