Cover Picture

The cover picture shows a false-color image of wild-type Escherichia coli DH5(α) cells growing on an agar plate containing the indicator chromeazurol S. The siderophore enterobactin is secreted by iron-starved colonies, resulting in FeIII-depleted, decolorized halos. The inset scheme shows the pathway for enterobactin biosynthesis from 2,3-dihydroxybenzoic acid (2,3-DHB) and L-serine by the nonribosomal peptide synthetase (NRPS) enzymes EntE, EntB, and EntF. These enzymes catalyze the formation of peptide bonds without mRNA templates and have a modular structure. A functional module consists of an adenylation (A), a thiolation (T), and a condensation (C) domain. The terminal thioesterase (TE) domain of EntF catalyzes elongation and cyclotrimerization to the final product. Further details about the diversity and function of the chain-releasing C-terminal domains of NRPS assembly lines can be found in the Minireview by C. T. Walsh et al. on p. 99 ff.