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Pyrrolizidine alkaloids (PAs) are a group of natural products with important biological activities. The discovery and characterization of the multifunctional FAD-dependent enzyme LgnC is now described. The enzyme is shown to convert indolizidine intermediates into pyrrolizidines through an unusual ring expansion/contraction mechanism, and catalyze the biosynthesis of new bacterial PAs, the so-called legonmycins. By genome-driven analysis, heterologous expression, and gene inactivation, the legonmycins were also shown to originate from non-ribosomal peptide synthetases (NRPSs). The biosynthetic origin of bacterial PAs has thus been disclosed for the first time.

Heterocycle-containing cyclic peptides are promising scaffolds for the pharmaceutical industry but their chemical synthesis is very challenging. A new universal method has been devised to prepare these compounds by using a set of engineered marine-derived enzymes and substrates obtained from a family of ribosomally produced and post-translationally modified peptides called the cyanobactins. The substrate precursor peptide is engineered to have a non-native protease cleavage site that can be rapidly cleaved. The other enzymes used are heterocyclases that convert Cys or Cys/Ser/Thr into their corresponding azolines. A macrocycle is formed using a macrocyclase enzyme, followed by oxidation of the azolines to azoles with a specific oxidase. The work is exemplified by the production of 17 macrocycles containing 6–9 residues representing 11 out of the 20 canonical amino acids.

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Neocarazostatin A (NZS) is a bacterial alkaloid with promising bioactivities against free radicals, featuring a tricyclic carbazole nucleus with a prenyl moiety at C-6 of the carbazole ring. Here, we report the discovery and characterization of the biosynthetic pathway of NZS through genome mining and gene inactivation. The in vitro assays characterized two enzymes: NzsA is a P450 hydroxylase and NzsG is a new phytoene-synthase-like prenyltransferase (PTase). This is the first reported native PTase that specifically acts on the carbazole nucleus. Finally, our in vitro reconstituted experiment demonstrated a coupled reaction catalyzed by NzsG and NzsA tailoring the NZS biosynthesis.

The brominated tryptophan-derived ent-eusynstyelamide B (1) and three new derivatives, eusynstyelamides D, E, and F (2-4), were isolated from the Arctic bryozoan Tegella cf. spitzbergensis. The structures were elucidated by spectroscopic methods including 1D and 2D NMR and analysis of mass spectrometric data. The enantiomer of 1, eusynstyelamide B, has previously been isolated from the Australian ascidian Eusynstyela latericius. Antimicrobial activities are here reported for 1-4, with minimum inhibitory concentrations (MIC) as low as 6.25 μg/mL for 1 and 4 against Staphylococcus aureus. Eusynstyelamides 2 and 3 showed weak cytotoxic activity against the human melanoma A 2058 cell line.

Microorganisms living in extreme environments represent a huge reservoir of novel antimicrobial compounds and possibly of novel chemical families. Antarctica is one of the most extraordinary places on Earth and exhibits many distinctive features. Antarctic microorganisms are well known producers of valuable secondary metabolites. Specifically, several Antarctic strains have been reported to inhibit opportunistic human pathogens strains belonging to Burkholderia cepacia complex (Bcc). Herein, we applied a biodiscovery pipeline for the identification of anti-Bcc compounds. Antarctic sub-sea sediments were collected from the Ross Sea, and used to isolate 25 microorganisms, which were phylogenetically affiliated to three bacterial genera (Psychrobacter, Arthrobacter, and Pseudomonas) via sequencing and analysis of 16S rRNA genes. They were then subjected to a primary cell-based screening to determine their bioactivity against Bcc strains. Positive isolates were used to produce crude extracts from microbial spent culture media, to perform the secondary screening. Strain Pseudomonas BNT1 was then selected for bioassay-guided purification employing SPE and HPLC. Finally, LC-MS and NMR structurally resolved the purified bioactive compounds. With this strategy, we achieved the isolation of three rhamnolipids, two of which were new, endowed with high (MIC < 1 μg/mL) and unreported antimicrobial activity against Bcc strains.

Linaridins are rare linear ribosomally-synthesized and post-translationally modified peptides (RiPPs) and only two, cypemycin and SGR-1832, in this family have been identified so far. Legonaridin 1 has been discovered as a new member of linaridins through chemical isolation, peptidogenomics, comprehensive 1- and 2-D NMR and advanced Marfey's analyses from the soil bacterium Streptomyces sp. CT34, an isolate collected from Legon, Ghana. Bioinformatics analysis of the gene cluster suggested that the biosynthesis of legonaridin 1 is different from those of cypemycin and SGR-1832. Consistent with bioinformatics and peptidogenomics analyses, 1 has a total of nine post-modifications, 8 dehydrobutyrine residues and a N,N-dimethylated N-terminus with a carboxylic acid at the C-terminus. Legonaridin 1 is structurally different from the two known linaridins comprising a new subfamily. This is the first time that NMR spectroscopy is used to establish the 2-D structure of a linaridin RiPP.