Integrated Proteomics and Metabolomics reveal altered metabolic regulation of Xanthobacter autotrophicus under electrochemical water-splitting conditions

Biological-inorganic hybrid systems are a growing class of technologies that combine microorganisms with materials for many purposes including chemical synthesis, environmental remediation, and energy generation. Recently, hybrid systems have been developed toward the sustainable generation of value-added chemicals from the plentiful and potentially renewable resources of electricity, water, and air. These hybrid systems typically consider microorganisms as catalysts that essentially perform only the reaction of interest, however other metabolic activity may influence that reaction and thus the output of the entire system. This possibility renders the investigation of biological responses to the hybrid environment critical to future system development and optimization. The present study investigates this phenomenon in a recently reported hybrid system that uses electrochemical water-splitting to provide reducing equivalents to the nitrogen-fixing bacteria Xanthobacter autotrophicus for efficient reduction of N2 to biomass that may be used as fertilizer. Using integrated proteomic and metabolomic methods, we find a pattern of differentiated metabolic regulation under electrochemical water-splitting (hybrid) conditions. We further report an increased expression of proteins of interest, namely those responsible for nitrogen fixation and assimilation, which indicate increased rates of nitrogen fixation and support previous observations of faster biomass accumulation in the hybrid system compared to typical planktonic growth conditions. This work complicates the inert catalyst view of biological-inorganic hybrids while demonstrating the power of multi-omics analysis as a tool for deeper understanding of those systems.