Propionate metabolism in.

Abstract

Desulfurella acetivorans, a strictly anaerobic sulfur-reducing deltaproteobacterium, is capable of heterotrophic growth on acetate oxidation or autotrophic growth using molecular hydrogen. This study demonstrates that the organism can also utilize propionate as a carbon source. Although a putative operon encoding methylcitrate cycle enzymes is present in the genome, no corresponding enzymatic activity was detected in cell extracts from propionate-grown cultures. Isotope tracer experiments using uniformly labeled [U-13C]propionate, combined with comparative proteomic profiling of acetate- versus propionate-grown cells, revealed that propionyl-CoA is instead carboxylated to methylmalonyl-CoA, which is subsequently converted to succinyl-CoA. This intermediate enters the TCA cycle, where it is ultimately converted to oxaloacetate; condensation with acetyl-CoA then yields citrate for further oxidation. These findings underscore the limitations of genome-based metabolic predictions and the necessity of experimental validation for accurate pathway characterization.

Mechanism

Propionyl-CoA is carboxylated to methylmalonyl-CoA and then converted to succinyl-CoA, which enters the TCA cycle. Despite genomic evidence for a methylcitrate cycle operon, this pathway is not functionally active during propionate growth.