Biodiversity and Antifungal Activities of Amazonian Actinomycetes Isolated from Rhizospheres of Inga edulis Plants.

Background: Actinobacteria are major producers of antibacterial and antifungal metabolites and are growing their search for substances of biotechnological interest, especially for use in agriculture, among other applications. The Amazon is potentially rich in actinobacteria; however, almost no research studies exist. Thus, we present a study of the occurrence and antifungal potential of actinobacteria from the rhizosphere of Inga edulis, a native South American plant and one that is economically useful in the whole of the Amazon.

Methods: Among the 64 actinobacteria strains isolated from the rhizosphere of three Inga edulis plants, 20 strains were selected and submitted to dual-culture assays against five important phytopathogenic fungi and morphological and 16S rRNA gene analyses. Two strains, LaBMicrA B270 and B280, were also studied for production curves of metabolic extracts and antifungal activities, including their minimum inhibitory concentration (MIC) against phytopathogenic fungi.

Results: Among the 20 strains, 90% were identified as Streptomyces and 10% as Kitasatospora. All the strains showed antagonisms against two or more of five phytopathogens: Corynespora cassiicola, Colletotrichum guaranicola, Colletotrichum sp., Pestalotiopsis sp., and Sclerotium coffeicola. Streptomyces spp. strains LaBMicrA B270 and B280 were active against phytopathogens of the guarana plant (Paullinia cupana). Furthermore, AcOEt/2-propanol 9:1 extract from the 10-day strain LaBMicrA B280 cultured medium presented activity against all the phytopathogens tested, with a minimum inhibitory concentration of 125 μg/mL.

Conclusions: The results revealed various actinomycetes in three rhizospheres of I. edulis in the Amazon and the high potential of metabolic extracts from some of these bacterial strains against phytopathogenic fungi that destroy numerous crops.