FIGURE 1.

The model-predicted essential pathway catalyzed by AldA. Glycolaldehyde is a by-product of the essential tetrahydrofolate synthesis pathway in Escherichia coli. It is produced by dihydroneopterin aldolase, encoded by the gene folB. The aldA gene encodes glycolaldehyde dehydrogenase, which oxidizes glycolaldehyde to glycolate. In an ΔaldA knockout strain, the E. coli metabolic model predicts that glycolaldehyde will accumulate in the cell, leading to cell death (Orth et al., 2011). Experimentally, however, ΔaldA mutants are viable.