Updated project metadata. The Trypanosoma brucei genome contains three fumarate reductase (FRD) genes, including two tandemly arranged in chromosome 5 encoding the glycosomal isoform (FRDg) and a potentially mitochondrial FRD isoform never detected so far in trypanosomes (FRDm2). We report here that the PPDK/PEPCK/GPDH mutant cell line (Δppdk/Δpepck/RNAi-GPDH) expresses a chimeric non-functional FRDg-m2 isoform resulting from stochastic homologous recombination within the FRDg/FRDm2 locus. This conclusion come from comparison of the parental (WT, Δppdk, Δpepck and Δppdk/Δpepck) and Δppdk/Δpepck/RNAi-GPDH proteomes. The selective advantage provided by the consequential loss of the FRDg gene, in the context of the Δppdk/Δpepck/RNAi-GPDH null background, is probably related to the autoflavinylation activity of the FRDg isoform.