Fig. 2: Maladicin biosynthesis, heterologous expression and structure.

a,b, The malacidin BGC was recovered on three overlapping cosmid clones (a) and assembled from these three overlapping clones in yeast using transformation-associated recombination (TAR) (b). The resulting BAC was integrated into the S. albus genome for heterologous expression studies. c, A representative HPLC analysis of crude extracts derived from cultures of S. albus transformed with the malacidin BGC shows the presence of BGC-specific small molecules. The two primary malacidin peaks are highlighted with an asterisk. d, Unlike crude extracts of the S. albus host strain alone, only extracts from the S. albus harbouring the malacidin BGC showed antibacterial activity when applied to a lawn of S. aureus USA300. Both the HPLC analysis (c) and antibacterial activity (d) are representative of four independent fermentations. e, Malacidin A and B are cyclic lipopeptides containing eight-amino-acid macrocycles and polyunsaturated lipids. The malacidins do not contain the conserved DXDG motif seen in all known calcium-dependent antibiotics—incorporating a rare 3-hydroxyl aspartic acid (HyAsp, highlighted in violet) and lacking the spacer residue. Biosynthetic enzymes predicted to be involved in the production of non-proteinogenic amino acid (3-methyl aspartic acid, 4-methyl proline and 2,3-diamino 3-methyl propanoic acid) and fatty acid substrates required for the biosynthesis of the maladicins are shown and colour-coded according to their activities. Stereocentres in malacidin that were predicted bioinformatically, as opposed to through chemical and spectroscopic analysis, are denoted with an asterisk.