Valine overproduction in Methanothermobacter marburgensis with temperature-induced promoter system and allosteric resistant acetolactate synthase variants.

In times of a climate crisis caused by extreme emissions of green-house gases on a global scale, mitigation solutions need to be found. One solution is the system of carbon capture and utilization (CCU), where C1 gases, such as carbon monoxide (CO), carbon dioxide (CO2), or methane, are either redirected from industrial off-gas streams or directly air-captured. A biotechnological process for CCU is the use of Methanothermobacter marburgensis for CO2 fixation and production of value-added compounds. In this study, we focused on valine production, an amino acid important for human or feedstock nutrition. We demonstrated overproduction of valine from CO2 in M. marburgensis with temperature-induced promoters. Here, we reached a 12.9-fold increase in valine production between the OFF- and ON states of the inducible promoter with a maximal specific production rate of 14.17 mg gCDW-1 h-1 of valine in closed batch experiments. In the second approach for valine production, we overexpressed acetolactate synthase genes with resistance to allosteric valine inhibition from Methanothermobacter thermautotrophicus recombinant in M. marburgensis. We identified a strong reduction in allosteric inhibition towards valine. This resulted in specific valine productivity of up to 40 mg gCDW-1 h-1 and states the highest specific productivity on an individual amino acid in methanogens. With those findings, we expanded the toolbox for genetic modification of M. marburgensis by a thermo-inducible promoter system and applied protein engineering for enhanced production of value-added compounds to M. marburgensis. This proof of concept shows the feasibility of archaeal cell factories generation via genetic engineering for industrial production of value-added compounds with thermophilic methanogens.