Assimilation of formic acid and CO by engineered equipped with reconstructed one-carbon assimilation pathways.

Gaseous one-carbon (C1) compounds or formic acid (FA) converted from CO can be an attractive raw material for bio-based chemicals. Here, we report the development of strains assimilating FA and CO through the reconstructed tetrahydrofolate (THF) cycle and reverse glycine cleavage (gcv) pathway. The formate-THF ligase, methenyl-THF cyclohydrolase, and methylene-THF dehydrogenase genes were expressed to allow FA assimilation. The gcv reaction was reversed by knocking out the repressor gene () and overexpressing the genes. This engineered strain synthesized 96% and 86% of proteinogenic glycine and serine, respectively, from FA and CO in a glucose-containing medium. Native serine deaminase converted serine to pyruvate, showing 4.5% of pyruvate-forming flux comes from FA and CO The pyruvate-forming flux from FA and CO could be increased to 14.9% by knocking out , , and , chromosomally expressing under , and overexpressing the reconstructed THF cycle, , and genes in one vector. To reduce glucose usage required for energy and redox generation, the formate dehydrogenase (Fdh) gene was expressed. The resulting strain showed specific glucose, FA, and CO consumption rates of 370.2, 145.6, and 14.9 mg⋅g dry cell weight (DCW)⋅h, respectively. The C1 assimilation pathway consumed 21.3 wt% of FA. Furthermore, cells sustained slight growth using only FA and CO after glucose depletion, suggesting that combined use of the C1 assimilation pathway and Fdh will be useful for eventually developing a strain capable of utilizing FA and CO without an additional carbon source such as glucose.