Potential biodiversity and antifungal activities of Amazonian actinomycetes isolated from rhizosphere of Inga edulis plants

Abstract

Abstract Actinobacteria are major producers of antibacterial and antifungal metabolites and are targets of increasing research in the search for substances of biotechnological interest, especially for use in medicine and agriculture. The Amazon is potentially rich in actinobacteria, in turn poorly studied. Thus, we prospected actinobacteria from the rhizosphere of the South America native plant Inga edulis, which produces edible fruits and is economically useful in the whole Amazon region. Among all 64 strains of actinobacteria isolated, 20 strains representing 16 morphogroups were subjected to morphological analysis, genotyping using the 16S rRNA gene, and dual-culture assays against pathogenic fungi of important agricultural plants in the region that also cause annual losses of millions of dollars to world agriculture. Using GenBank-NCBI and EzBioCloud data, 90% of the strains were identified as Streptomycesand 10% as Kitasatospora, indicating at least 16 specific species and possibly new species. All strains showed antagonisms for two or more different phytopathogens as Corysnepora cassiicola, Colletotrichum sp., Colletotrichum guaranicola, Pestalotiopsis sp., and Sclerotium coffeicola. The strains Streptomyces spp. LaBMicrA B270 and B280 stood out mainly against phytopathogens of the guarana plant (Paullinia cupana), an important crop for the regional economy and one of the best sources of caffeine in the world, whose powder is used in the food industry and traditional medicine. Furthermore, the acetate/isopropanol extract from the 10-day LaBMicrA B280 cultured medium presents fungistatic or fungicidal for all phytopathogens tested with a minimum inhibitory concentration (MIC) of 125 μg/mL.