Figure 1. Amino acid composition of insulin. The A and B chains are linked by two disulfide bridges between cysteine residues (Cys). An additional disulfide bridge connects two cysteine residues within the A chain. (Diagram: Anne Kemmling, Goettingen, Germany.)

Figure 2. Construction of an E. coli strain able to synthesize 1,3-propanediol from glucose. Two genes have been introduced from the yeast Saccharomyces cerevisiae, which are able to convert dihydroxyacetone phosphate to glycerol. Furthermore, the B ₁₂-containing glycerol dehydratase genes from Klebsiella pneumonia have been introduced. yqh is a dehydrogenase converting beta-hydroxypropionaldehyde into 1,3-propanediol. Certain pathways in the production strain have been blocked, as in the ethanol production strain depicted in Figure 1b. (Diagram: Petra Ehrenreich, Goettingen, Germany.)

Figure 3. Electronmicrograph of Ralstonia eutropha cells accumulating poly-beta-hydroxybutyric acid (PHB) during growth. Pictures were taken after 3, 12, and 24 hours of growth. (Hans Guenter Schlegel et al. Nature 191, 463–465, 1961.)