Electrochemical monitoring of electroactive compounds secreted by Escherichia coli during the aerobic-to-anaerobic transition.

Escherichia coli is a metabolically adaptable microorganism and secrets some metabolites including electroactive metabolites to maintain intracellular redox balance depending on environmental oxygen levels. To the best of our knowledge, this is the first preliminary report for electrochemical monitoring of electroactive metabolites secreted by E. coli supplied with glucose during the aerobic-to-anaerobic transition. The reduction current detected at the aerobically cultured E. coli-modified carbon felt electrode connected to Pt lead wire increased upon sequential addition of fumarate and glucose during the aerobic-to-anaerobic transition. Cyclic voltammetric data, along with inhibitor studies suggested that one of the electroactive compounds that most strongly contributed to the current response was protons probably originated from the metabolically-overflowed organic acids from E. coli. Moreover, it was found that E. coli supplied with glucose during the aerobic-to-anaerobic transition secreted NAD+ and NADH at the nanomolar levels in the electrochemical measurement solution.