Oceanic harmful algal blooms of Pseudo-nitzschia diatoms produce the potent mammalian neurotoxin domoic acid (DA). Despite decades of research, the molecular basis for its biosynthesis is not known. By using growth conditions known to induce DA production in Pseudo-nitzschia multiseries, we implemented transcriptome sequencing in order to identify DA biosynthesis genes that colocalize in a genomic four-gene cluster. We biochemically investigated the recombinant DA biosynthetic enzymes and linked their mechanisms to the construction of DA’s diagnostic pyrrolidine skeleton, establishing a model for DA biosynthesis. Knowledge of the genetic basis for toxin production provides an orthogonal approach to bloom monitoring and enables study of environmental factors that drive oceanic DA production.

In the ongoing effort to unlock the chemical potential of marine bacteria, genetic engineering of biosynthetic gene clusters (BGCs) is increasingly used to awake or improve expression of biosynthetic genes that may lead to discovery of novel bioactive natural products. Previously, we reported the successful capture, engineering and heterologous expression of an orphan BGC from the marine actinomycete Saccharomonospora sp. CNQ-490, which resulted in the isolation of the novel lipopeptide antibiotic taromycin A. Herein we report the isolation and structure elucidation of taromycin B, the second most abundant product of the taromycin biosynthetic series, and show that taromycins A and B exhibit complex chromatographic properties indicative of interconverting conformations. Taromycins A and B display potent activity against methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium clinical isolates, suggestive that the taromycin molecular scaffold is a promising starting point for further derivatization to produce compounds with promising antibiotic characteristics.

Highlights d Streptophenazine biosynthetic pathway (spz) was cloned from marine Streptomyces d Refactoring the spz pathway led to tremendous chemical diversity (112 compounds) d Streptophenazines with N-formylglycine moiety show potent antibiotic activity d Discrete adenylation protein is required to produce Nformylglycine analogs

l-4-Chlorokynurenine (l-4-Cl-Kyn) is aneuropharmaceutical drug candidate that is in development for the treatment of major depressive disorder.R ecently,t his amino acid was naturally found as ar esidue in the lipopeptide antibiotic taromycin. Herein, we report the unprecedented conversion of l-tryptophan into l-4-Cl-Kyn catalyzedbyfour enzymes in the taromycin biosynthetic pathway from the marine bacterium Saccharomonospora sp.CNQ-490. We used genetic, biochemical, structural, and analytical techniques to establish l-4-Cl-Kyn biosynthesis,w hichi si nitiated by the flavin-dependent tryptophan chlorinaseT ar14 and its flavin reductase partner Tar15. This work revealed the first tryptophan 2,3-dioxygenase (Tar13) and kynurenine formamidase (Tar16) enzymes that are selective for chlorinated substrates. The substrate scope of Tar13, Tar14, and Tar16 was examined and revealed intriguing promiscuity,therebyopening doors for the targeted engineering of these enzymes as useful biocatalysts.Supportinginformation (including experimental information) and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.