The cysteines of most cytoplasmic proteins are maintained in the reduced state; although disulfide bonds can form transiently, they are rapidly reduced. In Escherichia coli, the thioredoxin and glutaredoxin/glutathione pathways catalyze disulfide bond reduction. The thioredoxins are reduced by thioredoxin reductase (encoded by trxB ), while the glutaredoxins are kept in the reduced state by glutathione, which is reduced by glutathione reductase (encoded by gor). A substrate of these reductive pathways is the essential enzyme ribonucleotide reductase (RNR). Strains that lack both the thioredoxin and glutaredoxin/glutathione pathways cannot grow because they accumulate RNR in the oxidized, inactive state. Our lab has used suppressor analysis to evolve and characterize new pathways of disulfide bond reduction. For example, suppressor mutations convert the peroxidase AhpC to a disulfide reductase, which restores electron flow to trxB gor mutants. In this work, we describe suppressor mutations of a trxB gor ahpC strain that alter the gene IpdA, which encodes the oxidoreductase lipoamide dehydrogenase. LpdA normally oxidizes the lipoic acid cofactor (dihydrolipoamide) that is bound to proteins in two multienzyme complexes involved in the TCA cycle. Suppressor mutations in IpdA decrease the activity of the enzyme, allowing dihydrolipoamide to accumulate and be used as a source of electrons for the reduction of RNR. Our genetic analysis of the suppressor strain suggests that dihydrolipoamide reduces the glutaredoxins, effectively substituting for glutathione. At the same time, the glutaredoxins oxidize dihydrolipoamide, substituting for lipoamide dehydrogenase. Thus, a combination of mutations has functionally rewired two pathways. We suggest that this pathway might function in organisms other than E. coli, and performed bioinformatic analysis to identify a set of candidate organisms that might use dihydrolipoamide to reduce their glutaredoxins. We also have identified factors that might affect the use of this novel pathway for disulfide bond reduction. Specifically, it appears that dihydrolipoamide oxidation and TCA cycle function is important for the growth of these suppressor strains. In addition, we have obtained suppressors of a strain lacking the thioredoxins and glutaredoxin that define additional factors involved in regulating ribonucleotide reductase expression.