Mining Symbionts of a Spider‐Transmitted Fungus Illuminates Uncharted Biosynthetic Pathways to Cytotoxic Benzolactones

Abstract

A spider-transmitted fungus (Rhizopus microsporus) that was isolated from necrotic human tissue was found to harbor endofungal bacteria (Burkholderia sp.). Metabolic profiling of the symbionts revealed a complex of cytotoxic agents (necroximes). Their structures were characterized as oxime-substituted benzolactone enamides with a peptidic side chain. The potently cytotoxic necroximes are also formed in symbiosis with the fungal host and could have contributed to the necrosis. Genome sequencing and computational analyses revealed a novel modular PKS/NRPS assembly line equipped with several non-canonical domains. Based on gene-deletion mutants, we propose a biosynthetic model for bacterial benzolactones. We identified specific traits that serve as genetic handles to find related salicylate macrolide pathways (lobatamide, oximidine, apicularen) in various other bacterial genera. Knowledge of the biosynthetic pathway enables biosynthetic engineering and genome-mining approaches.Supporting information and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.org/10.

Genome Mining of Oxidation Modules in trans‐Acyltransferase Polyketide Synthases Reveals a Culturable Source for Lobatamides

“…Their related structures and the identification of bacterial sources suggest that all of these compounds are of prokaryotic origin. For an expansion of this family, see a study on necroximes that was conducted concurrently with this work [23] …”

Five Surfactin Isomers Produced during Cheonggukjang Fermentation by Bacillus pumilus HY1 and Their Properties

“…A number of recent studies have focused on the anticancer activities of CLP. Kameda et al [ 9 ] provided the first evidence that CLP has anticancer activity based on the fact that extracted CLP from B. natto KMD 2311 can induce apoptosis of cancer cells. 35.…”

“…Surfactin is produced non-ribosomally by multienzyme complexes called nonribosomal peptide synthetases [ 6 ]. The small microbial peptides produced via non-ribosomal pathways had demonstrated potent biological activities and growing economic value in uses such as drugs, e.g., antibiotics [ 7 ], cytotoxic benzolactones [ 8 ], alkaloids [ 9 ], or as food additives [ 10 ]. Surfactin is composed of one β-hydroxy fatty acid molecule with a long fatty acid moiety, linked to a seven amino acid peptide to form a lactone ring [ 11 ].…”

Mining and unearthing hidden biosynthetic potential

“…The endofungal bacteria also produce cytotoxic necroximes (e.g., necroxime A, 33) in symbiosis with the fungal host. These benzolactones are biosynthesized by a modular PKS/NRPS assembly line and may contribute to the pathogenic phenotypes ascribed to the fungal host 120 . A genomeguided chemical profiling of a marine bacterium from the rhizosphere of the halophilic plant Carex scabrifolia yielded a number of chemically diverse natural products, some of which possess potent cytostatic activity 121 .…”