(62b) Characterizing the Interplay between Rubisco and Nitrogenase Enzymes of Rhodopseudomonas Palustris

Rhodopseudomonas palustris CGA009 (R. palustris) is a gram-negative purple non-sulfur bacteria that can grow either phototrophically or chemotrophically. It does so by fixing or utilizing a diverse range of substrates, including one of the most abundant sources of carbon, lignin breakdown products, to meet its carbon and nitrogen requirements. It can grow aerobically or anaerobically and generate energy from light, inorganic, and organic compounds. Due to its ability to convert different carbon sources into useful products in anaerobic mode, this study, for the first time, reconstructed a metabolic and expression (ME-) model of R. palustris to investigate its anaerobic-photoheterotrophic growth. ME-models, as opposed to metabolic (M-) models, include transcription and translation reactions, as well as macromolecule synthesis, and couple these reactions with growth rate. This distinct feature of the ME-model resulted in nonlinear growth curve predictions that closely matched experimental growth rate data. The ME-model predicted malate dehydrogenase and glycerol-3 phosphate dehydrogenase as alternate electron sinks at the theoretical maximum growth rate. Furthermore, the ME-model identified ferredoxin as a key regulator in electron distribution between two major redox balancing pathways. Since ME-models include the turnover rate for each metabolic reaction, the model in this work was successfully used to capture the experimentally observed temperature regulation of various nitrogenases. Overall, these unique features of the ME-model demonstrated the influence of nitrogenases and rubiscos on R. palustris growth and predicted a key regulator in distributing electrons between major redox balancing pathways, thus establishing a platform for in silico investigation of R. palustris metabolism from a multi-omics perspective.