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

The genus <i>Streptomyces</i> 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 <i>Streptomyces</i> 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 <i>in vitro</i> in dual cultures against <i>Phytophthora palmivora</i>, <i>Colletotrichum acutatum</i>, <i>Fusarium oxysporum</i>, <i>Rhizoctonia solani</i>, <i>Sclerotinia sclerotiorum</i>, and <i>Fusarium graminearum</i>. 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 <i>P. palmivora</i>. Moreover, the growth inhibition of <i>Colletotrichum gloeosporioides</i> by albonoursin and the antibacterial effect of 2-chloroadenosine and 5'-O-sulfamoyl-2-chloroadenosine against <i>Pectobacterium carotovorum</i> 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 <i>in vitro</i> bioassays on cacao pods (<i>Theobroma cacao</i> L.) inoculated with the antagonist strain and <i>P. palmivora</i> APB-35, demonstrate that <i>Streptomyces</i> sp. Caat 5-35 is a source of natural products with applications in agriculture and could serve as an alternative for crop protection.