Discovery of the Tiancilactone Antibiotics by Genome Mining of Atypical Bacterial Type II Diterpene Synthases

Abstract

Although genome mining has advanced the identification, discovery, and study of microbial natural products, the discovery of bacterial diterpenoids continues to lag behind. Herein, we report the identification of 66 putative producers of novel bacterial diterpenoids, and the discovery of the tiancilactone (TNL) family of antibiotics, by genome mining of type II diterpene synthases that do not possess the canonical DXDD motif. The TNLs, which are broad-spectrum antibiotics with moderate activities, are produced by both Streptomyces sp. CB03234 and Streptomyces sp. CB03238 and feature a highly functionalized diterpenoid skeleton that is further decorated with chloroanthranilate and γ-butyrolactone moieties. Genetic manipulation of the tnl gene cluster resulted in TNL congeners, which provided insights into their biosynthesis and structure-activity relationships. This work highlights the biosynthetic potential that bacteria possess to produce diterpenoids and should inspire continued efforts to discover terpenoid natural products from bacteria.

WblA, a global regulator of antibiotic biosynthesis in Streptomyces

“…Streptomyces sp. CB03234 is a native producer of both ten-membered enediyne tiancimycins (TNMs) and diterpernoid tiancilactones (TNLs) (Dong et al, 2018 ; Yan et al, 2016 ). Among the TNMs discovered, both TNM-A and TNM-D showed superior cytotoxic activities against several cancer cell lines (Yan et al, 2016 , 2018 ).…”

Characterization of TnmH as an O-Methyltransferase Revealing Insights into Tiancimycin Biosynthesis and Enabling a Biocatalytic Strategy To Prepare Antibody–Tiancimycin Conjugates

“…We have since characterized this family of metabolites as tiancilactones and cloned and characterized its biosynthetic gene cluster (Figure S3). 24 Progress has also been made in improving TNM production by subjecting the wild-type S. sp. CB03234 to multiple rounds of strain improvement.…”

Atolypenes, Tricyclic Bacterial Sesterterpenes Discovered Using a Multiplexed In Vitro Cas9-TAR Gene Cluster Refactoring Approach

“…39–42 Gene clusters encoding Class II terpene cyclases are of particular interest to us because they are predicted to cyclize large isoprene precursors (>20 carbons) which have only rarely been reported in bacteria. 38, 42, 43 We have initially focused our discovery efforts on a predicted Class II cyclase-containing gene cluster, found in the genome of A. tolypomycina, which we have called the ato gene cluster. Based on gene organization and gene content, the genomic region directly adjacent to the predicted atoE Class II terpene cyclase is closely related to the brasilicardin A ( bra ) gene cluster found in the genome of Nocardia brasiliensis IFM 0406 (also referred to as Nocardia terpenica ).…”

“…Historically, the vast majority of terpenes have been found from plants and fungi, with a relatively minor fraction having been isolated from bacterial sources . Bioinformatic analysis of the rapidly growing number of sequenced bacterial (meta)­genomes suggests that bacteria should also represent a fertile source of novel, biologically interesting terpenes. − Gene clusters encoding Class II terpene cyclases are of particular interest to us because they are predicted to cyclize large isoprene precursors (>20 carbons) which have only rarely been reported in bacteria. ,, We have initially focused our discovery efforts on a predicted Class II cyclase-containing gene cluster, found in the genome of A. tolypomycina, which we have called the ato gene cluster.…”