Abstract
BackgroundCupriavidus necator is the best-studied knallgas (also termed hydrogen oxidizing) bacterium and provides a model organism for studying the production of the storage polymer polyhydroxybutyrate (PHB). Genetically engineered strains could be applied for the autotrophic production of valuable chemicals. Nevertheless, the efficiency of the catalyzed processes is generally believed to be lower than with acetogenic bacteria. Experimental data on the potential efficiency of autotrophic production with C. necator are sparse. Hence, this study aimed at developing a strain for the production of the bulk chemical acetoin from carbon dioxide and to analyze the carbon and electron yield in detail.ResultsWe developed a constitutive promoter system based on the natural PHB promoter of this organism. Codon-optimized versions of the acetolactate dehydrogenase (alsS) and acetolactate decarboxylase (alsD) from Bacillus subtilis were cloned under control of the PHB promoter in order to produce acetoin from pyruvate. The production process’s efficiency could be significantly increased by deleting the PHB synthase phaC2. Further deletion of the other PHB synthase encoded in the genome (phaC1) led to a strain that produced acetoin with > 100% carbon efficiency. This increase in efficiency is most probably due to a minor amount of cell lysis. Using a variation in hydrogen and oxygen gas mixtures, we observed that the optimal oxygen concentration for the process was between 15 and 20%.ConclusionTo the best of our knowledge, this study describes for the first time a highly efficient process for the chemolithoautotrophic production of the platform chemical acetoin.
Highlights
Cupriavidus necator is the best-studied knallgas bacterium and provides a model organism for studying the production of the storage polymer polyhydroxybutyrate (PHB)
This study focused on the production of the platform chemical acetoin
An outline of the central carbon metabolism of C. necator H16 is given in Additional file 4: Figure S4
Summary
Cupriavidus necator is the best-studied knallgas ( termed hydrogen oxidizing) bacterium and provides a model organism for studying the production of the storage polymer polyhydroxybutyrate (PHB). Engineered strains could be applied for the autotrophic production of valuable chemicals. This study aimed at developing a strain for the production of the bulk chemical acetoin from carbon dioxide and to analyze the carbon and electron yield in detail. Biotechnology can be the key to the advent of a bioeconomy as this technology can use renewable resources for sustainable production processes. C. necator is a model organism for both polyhydroxybutyrate (PHB) production and chemolithoautotrophic growth. C. necator can use carbon dioxide (CO2) as a carbon source, hydrogen (H2) as an electron donor, and oxygen (O2) as an electron acceptor. Multiple studies present strains that produce a large variety of chemicals ranging, for example, from α-humulene (over isopropanol, methyl ketones, and isobutanol) to Windhorst and Gescher Biotechnol Biofuels (2019) 12:163
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