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

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.

A Sustainable Chemicals Manufacturing Paradigm Using CO2 and Renewable H2

“…When the genes producing C. necator's natural carbon sink, polyhydroxybutyrate (phb), are attenuated, the cell accumulates pyruvate as the central metabolite under nutrient limitation, which can be redirected to a number of different carbon products (Steinbü chel and Schlegel, 1989). Consequently, metabolic engineering of C. necator to produce chemicals from CO 2 and H 2 has demonstrated promise, most notably in the production of (1) 2-hydroxyisobutyrate for Plexiglas (Przybylski et al, 2012), (2) isobutanol (Brigham et al, 2013), (3) 3-methyl-1-butanol (Li et al, 2012), (4) methyl ketones (Mü ller et al, 2013), ( 5) isopropanol (Marc et al, 2017), ( 6) a-humulene (Krieg et al, 2018), and ( 7) acetoin (Windhorst and Gescher, 2019). These studies have contributed appreciably to advancing the metabolic engineering of C. necator as a platform for using CO 2 as a carbon feedstock, noting that the focus was not on process engineering considerations.…”

Carbon Sources for Biomass, Food, Fossils, Biofuels and Biotechnology - Review Article

“…urgent need has risen for clean and sustainable bioproduction and alternatives to an economy predominantly depending on fossil resources, (Brandberg et al, 2005;Przybylski et al, 2012). Growing food grains for the production of biofuels squanders land, water and energy resources being vital for the production of food, while our agricultural systems are concurrently degrading land, water, biodiversity and climate on a global scale.…”

Thermophilic Coenzyme B 12 -Dependent Acyl Coenzyme A (CoA) Mutase from Kyrpidia tusciae DSM 2912 Preferentially Catalyzes Isomerization of ( R )-3-Hydroxybutyryl-CoA and 2-Hydroxyisobutyryl-CoA

“…Currently most interesting, however, is a biotechnological synthesis route employing HCM for the industrial production of the poly(methyl methacrylate) precursor 2-hydroxyisobutyric acid from renewable carbon (11), having great potential to completely replace the established petrochemical processes. Accordingly, mutase-dependent synthesis of this important building block from simple sugars and carboxylic acids as well as from carbon dioxide has already been demonstrated at the lab scale (12)(13)(14)(15). Implementation of an industrial HCM process seems to be particularly feasible, as the metabolic route delivering the mutase substrate 3-hydroxybutyryl-CoA is part of a well-studied overflow metabolism in bacteria.…”