A novel mechanistic insight into CO2 effects on chain elongation in Clostridium kluyveri based on transcriptomic and ¹³C-targeted metabolomic analyses.

Chain elongation is an important technology for processing organic wastewater (such as brewing wastewater), and Clostridium kluyveri is one of the most crucial microorganisms involved. This study aims to investigate the regulatory mechanism of inorganic carbon (IC) on the growth and metabolic pattern of Clostridium kluyveri. Results revealed that the production of caproate by Clostridium kluyveri from ethanol and acetate is a growth-coupled fermentation type and regulated by IC. With increased IC concentration, both the efficiency of caproate synthesis and the growth rate of Clostridium kluyveri improve to varying degrees. Based on transcriptomic and metabolomic analyses, IC promotes caproate production through enhancing flavin mononucleotide and flavin adenine dinucleotide which are crucial for the Reversed beta-oxidation cycle. 13C-labeled targeted metabolomics further reveal that IC plays a key role in the nutrient and genetic material synthesis in Clostridium kluyveri, as well as its energy metabolism. IC significantly contributes to electron transport and energy supply as evidenced by enhanced cofactors synthesis (NAD+, NADP+). IC also participates in the synthesis of 13 amino acids as well as nucleotides (AMP, GMP, CMP, UMP).