Electrochemical Investigation of Isoprenoid Quinone Productions by Shewanella oneidensis MR-1 Detected by Its Destructive Adsorption on an Indium-Tin-Oxide Electrode

Abstract

Ubiquinone and menaquinone play important roles in microbial respiratory chains. S. oneidensis is a facultative anaerobe, and it has been known that this microbe requires menaquinone (MK) and/or methylmenaquinone (MMK) to reduce inorganic and organic compounds, such as Fe(III), Mn(IV), fumarate, and nitrate, under anaerobic conditions. In this article, we show that voltammetry is useful to quantify ubiquinone (UQ), MK and MMK located in the cytoplasmic membrane simply by heating the microbe (thermal lysis) deposited on an indium-tin oxide electrode. It was found that the microbe predominantly produced UQ under aerobic conditions, while the production was switched to that of MMK under anaerobic conditions. This transition occurred at a dissolved oxygen concentration of ∼0.3 mg L−1. It was also found in this study that the total quinone concentration (UQ + MK + MMK) in a single cell was constant at all stages of the culture in a nutrition broth, suggesting that the cytoplasmic membrane was saturated with the quinones. The reduction of Fe(III) citrate with S. oneidensis was also studied. It was found that this microbe decreased the UQ and MMK levels to 45% and 39% of the initial values, respectively, after finishing the reduction.