Third-generation feed stocks for the clean and sustainable biotechnological production of bulk chemicals: synthesis of 2-hydroxyisobutyric acid

Abstract

Abstract Background The synthesis of 2-hydroxyisobutyric acid (2-HIB), a promising building block for, e.g., Plexiglas® production, is described as an example for a clean and sustainable bioproduction. Methods A derivative strain of Cupriavidus necator H16, impaired in the poly-ß-hydroxybutyrate synthesis pathway and equipped with xenogenic 2-hydroxyisobutyryl-coenzyme A mutase from Aquincola tertiaricarbonis L108, was applied. Batch cultivation was performed in the presence of vitamin B12 by supplying a gas mixture comprising hydrogen, oxygen, and carbon dioxide. Results Exploiting the chemo-litho-autotrophic potential of this so-called knallgas bacterium, 2-HIB was synthesized and excreted into the cultivation broth under aerobic conditions when inorganic nitrogen-limited conditions allowed an overflow metabolism of carbon metabolites. 2-HIB synthesis proceeded at a rate of 8.58 mg/[(g bacterial dry mass)·h]. Approximately 400 mg/L in total was obtained. The results were subsequently compared to calculated model data to evaluate the efficiency of the conversion of the substrates into the product. To achieve overall yield data regarding the substrate conversion, the model describes an integral process which includes both 2-HIB synthesis and biomass formation. Conclusions This study has confirmed the feasibility of the microbial synthesis of the bulk chemical 2-HIB from hydrogen and carbon dioxide by exploiting the chemo-litho-autotrophic metabolism of C. necator H16 PHB−4, additionally expressing the foreign 2-HIB-coenzyme A mutase. The product synthesis was satisfying as a proof of principle but does not yet approach the maximum value as derived from the model data. Furthermore, the biosynthesis potential of an optimized process is discussed in view of its technical application.