Phototrophic extracellular electron uptake is linked to carbon dioxide fixation in the bacterium Rhodopseudomonas palustris

Abstract

Extracellular electron uptake (EEU) is the ability of microbes to take up electrons from solid-phase conductive substances such as metal oxides. EEU is performed by prevalent phototrophic bacterial genera, but the electron transfer pathways and the physiological electron sinks are poorly understood. Here we show that electrons enter the photosynthetic electron transport chain during EEU in the phototrophic bacterium Rhodopseudomonas palustris TIE-1. Cathodic electron flow is also correlated with a highly reducing intracellular redox environment. We show that reducing equivalents are used for carbon dioxide (CO2) fixation, which is the primary electron sink. Deletion of the genes encoding ruBisCO (the CO2-fixing enzyme of the Calvin-Benson-Bassham cycle) leads to a 90% reduction in EEU. This work shows that phototrophs can directly use solid-phase conductive substances for electron transfer, energy transduction, and CO2 fixation.

Modeling the Interplay between Photosynthesis, CO2Fixation, and the Quinone Pool in a Purple Non-Sulfur Bacterium

“…glycogen). Furthermore, recent experimental work with R. palustris TIE-1 reported the presence of an unidentified quinol-oxidizing reaction that had not been accounted for previously 40 , giving further support to this prediction. To determine the effect of the quinone pool on growth, pFBA simulations were conducted under different quinol sink rates to qualitatively predict how changes in the quinone redox state affected the rest of the metabolic network.…”

Direct cathodic electron uptake coupled to sulfate reduction by Desulfovibrio ferrophilusIS5 biofilms

“…One explanation for the inhibitory effect of MoO 4 2− on current consumption and biofilm formation is a lack of available metabolic energy. We, therefore, tested whether metabolic energy is required for cathodic electron uptake of D. ferrophilus IS5 by treating cells with carbonyl cyanide m‐chlorophenylhydrazine (CCCP), a protonophore that dissipates the electrochemical membrane potential which is essential for energy conservation by sulfate respiration (Fitz and Cypionka, 1989; Kramer and Cypionka, 1989; Dilling and Cypionka, 1990) and consequently for cathodic current consumption (Rowe et al ., 2018; Guzman et al ., 2019). When CCCP was added to D. ferrophilus IS5, current consumption decreased but was not completely abolished unlike addition of molybdate (Fig.…”

Bioelectrochemical systems and synthetic biology: more power, more products

“…For example, microbial electrosynthesis of acetate from CO 2 and electrons has been demonstrated using both pure cultures and mixed microbial communities and has generally been dependent on hydrogen generation at the electrode where hydrogen serves as an electron transfer mediator to cells (Nevin et al ., ; Marshall et al ., , ; LaBelle and May, ). More recently, interesting progress has been made to develop photosynthetic autotrophs for microbial electrosynthesis applications (Guzman et al ., ).…”