# Novel Antimicrobial Activities of Albofungin, Albonoursin, and Ribonucleosides Produced by Streptomyces sp. Caat 5-35 Against Phytopathogens and Their Potential as a Biocontrol Agent

## TL;DR

This study explores a new Streptomyces strain that produces antimicrobial compounds effective against plant pathogens and could be used for crop protection.

## Contribution

The study reports the first anti-oomycete activity of albofungin and albonoursin against Phytophthora palmivora.

## Key findings

- Streptomyces sp. Caat 5-35 inhibited mycelial growth of several phytopathogens by 19% to 73.3%.
- Albofungin and albonoursin showed novel anti-oomycete activity against P. palmivora.
- 2-chloroadenosine and 5′-O-sulfamoyl-2-chloroadenosine exhibited antibacterial effects against Pectobacterium carotovorum.

## Abstract

The genus Streptomyces is the largest group within the phylum Actinobacteria, recognized for producing antibiotics and enzymes, with wide applications in medicine and biological control for crop protection against phytopathogens. In this study, the Streptomyces sp. Caat 5-35 strain, isolated from soil of the Caatinga biome in Brazil, and identified by analysis of the 16S rRNA gene, demonstrated its antagonistic effect in vitro in dual cultures against Phytophthora palmivora, Colletotrichum acutatum, Fusarium oxysporum, Rhizoctonia solani, Sclerotinia sclerotiorum, and Fusarium graminearum. Caat 5-35 inhibited mycelial growth ranging from 19% to 73.3%. Compounds purified by prep-HPLC from extracts were identified by spectral data analysis using UHPLC-triple-TOF-MS/MS, or nuclear magnetic resonance (NMR). This work demonstrated for the first time the anti-oomycete activity of albofungin, its derivatives, and albonoursin against P. palmivora. Moreover, the growth inhibition of Colletotrichum gloeosporioides by albonoursin and the antibacterial effect of 2-chloroadenosine and 5′-O-sulfamoyl-2-chloroadenosine against Pectobacterium carotovorum were demonstrated as novel findings. Caat 5-35 exhibited the ability to solubilize phosphates and produce cellulases on CMC agar. The findings of this study, in combination with in vitro bioassays on cacao pods (Theobroma cacao L.) inoculated with the antagonist strain and P. palmivora APB-35, demonstrate that Streptomyces sp. Caat 5-35 is a source of natural products with applications in agriculture and could serve as an alternative for crop protection.