Genomic scanning enabling discovery of a new antibacterial bicyclic carbamate-containing alkaloid
Date
2021
Journal Title
Journal ISSN
Volume Title
Publisher
Synthetic and Systems Biotechnology
Abstract
Non-ribosomal peptides are a group of structurally diverse natural products with various important therapeutic
and agrochemical applications. Bacterial pyrrolizidine alkaloids (PAs), containing a scaffold of two fused fivemembered
ring system with a nitrogen atom at the bridgehead, have been found to originate from a multidomain
non-ribosomal peptide synthetase to generate indolizidine intermediates, followed by multistep oxidation,
catalysed by single Bayer-Villiger (BV) enzymes, to yield PA scaffolds. Although bacterial PAs are rare in natural
product inventory, bioinformatics analysis suggested that the biosynthetic gene clusters (BGCs) that are likely to
be responsible for the production of PA-like metabolites are widely distributed in bacterial genomes. However,
most of the strains containing PA-like BGCs are not deposited in the public domain, therefore preventing further
assessment of the chemical spaces of this group of bioactive metabolites. Here, we report a genomic scanning
strategy to assess the potential of PA metabolites production in our culture collection without prior knowledge of
genome information. Among the strains tested, we found fifteen contain the key BV enzymes that are likely to be
involved in the last step of PA ring formation. Subsequently one-strain-many-compound (OSMAC) method,
supported by a combination of HR-MS, NMR, SMART 2.0 technology, and GNPS analysis, allowed identification
and characterization of a new [5 + 7] heterobicyclic carbamate, legoncarbamate, together with five known PAs,
bohemamine derivatives, from Streptomyces sp. CT37, a Ghanaian soil isolate. The absolute stereochemistry of
legoncarbamate was determined by comparison of measured and calculated ECD spectra. Legoncarbamate displays
antibacterial activity against E. coli ATCC 25922 with an MIC value of 3.1 μg/mL. Finally, a biosynthetic
model of legoncarbamate and other bohemamines was proposed based on the knowledge we have gained so far.
Description
Research Article
Keywords
Genomic scanning, Bayer villiger monooxygenase, Carbamate alkaloids, Pyrrolizidine alkaloids, Non-ribosomal peptide synthetases