Nigericin and Geldanamycin Are Phytotoxic Specialized Metabolites Produced by the Plant Pathogen Streptomyces sp. 11-1-2

• Published in: Microbiology Spectrum
• Main Authors: Gustavo A. Díaz-Cruz, Jingyu Liu, Kapil Tahlan, Dawn R. D. Bignell
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Society for Microbiology 2022
• Subjects: phytotoxins; molecular networking; biosynthetic gene clusters; specialized metabolites; Streptomyces; plant pathogens; Microbiology; QR1-502; Canada; Newfoundland
• Online Access: https://doi.org/10.1128/spectrum.02314-21; https://doaj.org/article/2e7e4872be3c4817ba393af0ac2251d9

ABSTRACT Streptomyces bacteria are a key source of microbial specialized metabolites with useful applications in medicine and agriculture. In addition, some species are important plant pathogens and cause diseases such as potato scab, which reduces the quality and market value of affected potato crops. Most scab-associated Streptomyces spp. produce the phytotoxic metabolite thaxtomin A as the principal pathogenicity factor. However, recent reports have described scab-causing strains that do not produce thaxtomin A, but instead produce other phytotoxins that are thought to contribute to plant host infection and symptom development. Streptomyces sp. 11-1-2 is a highly pathogenic strain that was originally isolated from a scab symptomatic potato tuber in Newfoundland, Canada. The strain secretes one or more phytotoxic compounds of unknown identity, and it is hypothesized that these compounds serve as virulence factors for this organism. We analyzed the genome sequence of Streptomyces sp. 11-1-2 and found biosynthetic gene clusters for producing the known herbicidal compounds nigericin and geldanamycin. Phytotoxic culture extracts were analyzed using liquid chromatography-coupled tandem mass spectrometry and molecular networking, and this confirmed the production of both compounds by Streptomyces sp. 11-1-2 along with other, potentially related metabolites. The biosynthesis of both metabolites was found to be suppressed by the addition of N-acetylglucosamine to the culture medium, and pure nigericin and geldanamycin were able to exhibit phytotoxic effects against both radish seedlings and potato tuber tissue. Furthermore, the coadministration of the two compounds produced greater phytotoxic effects against potato tuber tissue than administration of each compound alone. IMPORTANCE Plant pathogens use a variety of mechanisms, including the production of phytotoxic specialized metabolites, to establish an infection of host tissue. Although thaxtomin A is considered the key phytotoxin involved in the development of ...