Bioinformatics and Metabolic flux analysis highlight a new mechanism involved in lactate oxidation in Clostridium tyrobutyricum

Abstract

Abstract Background One of todays’ scientific challenge due to climate change and environmental issues is to find alternatives to the production of molecules of interest from petrochemistry. This study focuses on the understanding of the production of butyrate, hydrogen and CO2 from the oxidation of lactate with acetate in C. tyrobutyricum and thus propose an alternative carbon source to glucose. This species is known to produce more butyrate than the other butyrate-producing Clostridium species due to a lack of solventgenesis phase. The recent discoveries of flavin-based electron bifurcation mechanism as a mode of energy conservation have allowed us to propose a new metabolic scheme for the formation of butyrate from lactate-acetate co-metabolism. Results The search for genes encoding for EtfAB complexes and neighboring genes in the genome of C. tyrobutyricum identified a cluster of genes involved in butyrate formation and another cluster involved in lactate oxidation homologous to Acetobacterium woodii. A phylogenetic approach with other butyrate-producing and/or lactate-oxidizing species based on EtfAB complexes confirms these results with A. woodii and Clostridium kluyveri as references. A metabolic scheme on the production of butyrate, hydrogens and CO2 from the lactate-acetate co-metabolism in C. tyrobutyricum has been constructed. From data of steady-state continuous culture, an in silico metabolic carbon flux analysis model was built and made it possible to show the coherence of the scheme from the carbon recovery, the cofactor ratio and the ATP yield. Conclusions Bioinformatics analyzes have highlighted the use of flavin-based electron bifurcation. A metabolic scheme on the conversion of lactate and acetate has been proposed in C. tyrobutyricum, involving electron-transferring flavoprotein (Etf) complexes specific to the butyrate production and the lactate oxidation. The carbon metabolic fluxes analysis has validated this scheme involving the EtfAB complex at the origin of the oxidation of lactate in C. tyrobutyricum. This study contributes significantly to our understanding of the lactate oxidation metabolic pathways, the utility of the presence of acetate and the role of intracellular redox balance, and opens new perspectives for the production of molecules of interest as butyrate and hydrogen with C. tyrobutyricum.