P177: Identification of acetogenic 2,3-butanediol and lactate production pathways and reconstruction in metabolically engineered E. coli

2,3-Butanediol (23BDO) is a valuable commodity chemical used as a precursor for the manufacture of a variety of chemical products with an estimated world market sales value of $43 billion. Currently 23BDO is produced from petrochemicals, but it can also be synthesised by some pathogenic sugar eating bacteria.

We present here evidence of 23BDO and lactate production by three nonpathogenic acetogenic Clostridium species—C. autoethanogenum, C. ljungdahlii, and C. ragsdalei—using carbon monoxide (CO)-containing industrial waste gases or biomass syngas as the sole source of carbon and energy. A set of genes that are potentially involved in the production of 23BDO and lactate was identified in silico in C. ljungdahlii, which includes acetolactate synthase (alsS), acetolactate decarboxylase (alsD), 23BDO dehydrogenase (23BDH) and lactate dehydrogenase (ldhA). Homologous genes were also identified by in C. autoethanogenum and C. ragsdalei. A qPCR study of the genes involved in the proposed pathway showed a strong positive correlation between the identified biosynthetic genes and 23BDO and lactate production.

Expression of the three C. autoethanogenum genes, alsS, alsD and 23bdh, in E. coli confirmed production of 23BDO. Similarly, C. autoethanogenum ldh gene was able to restore lactate production in a ldh negative E. coli strain.

The proposed pathway for production of 23BDO from CO-eating bacteria offers the potential for non-reliance on petrochemicals and sugar feedstocks as well as a path towards a more sustainable fuel and chemical synthesis.