Electrochemically-driven CO2 and N2 capture by Azotobacter vinelandii

Abstract

Azotobacter vinelandii has been studied for over 100 years since its discovery as an obligate aerobic N2-fixing organism. This model bacterium enabled remarkable discoveries related to aerobic N2-fixation, respiration, microbial physiology, H2 production and assimilation, and enzyme kinetics, among others. Additionally, it is of great industrial interest due to its ability to produce bioplastics and alginate, and N2-fixation as an environmentally-friendly alternative to synthetic N-fertilizer in sustainable agriculture and industrial fermentations. Since these metabolic processes and derived applications are very-demanding in terms of cellular energy, this study aimed to analyze whether A. vinelandii can take electrons from a cathodically polarized electrode to enhance its metabolism. The observed electrochemical response and biomass composition indicated that, under microaerobic conditions, A. vinelandii can take electrons from an electrode to produce polyhydroxybutyrate-rich biomass even when no other carbon source than CO2 from the air was supplied. The addition of sucrose boosted not only polyhydroxybutyrate but also bulk protein accumulation suggesting a mixotrophic life-style comprising both electro-autotrophy from CO2 and electro-diazotrophy from N2. These findings open new venues for understanding the metabolic capabilities and flexibility of this remarkable bacterium, and pave the way to possibly novel biotechnological processes and applications.