Endophytic actinomycetes from Amphipterygium adstringens as potential producers of new pharmacological compounds.

The continuous search for bacterial secondary metabolites is a need and a consequence of the society’s growing demand for new compounds with pharmacological activities and improved properties. This search has been historically approached by selection of strains from different niches and evaluation of their biological activities. Endophytes are a relatively new source of molecules with potential biological activity. Among them, a great variety of bioactive compounds has been reported. In this study, two actinomycete isolated as endophytes from the bark tree Amphipterygium adstringens (used in traditional medicine in Mexico), were evaluated. Among them, one identified as Streptomyces scabrisporus and one as Actinoplanes sp. were selected for further characterization. Phylogenetic studies suggested Actinoplanes sp. as a new species. Dichloromethane (DCM) extracts from S. scabrisporus, tested against Micrococcus luteus and Bacillus subtilis gave minimum inhibitory concentrations (MIC) of 0.1 and 0.6 µg ml^-1, respectively. Extracts from Actinoplanes sp. showed MIC concentrations of 200 µg ml^-1 for the assay Gram-positive strains. When tested against the cancer cell lines MCF7, HeLa, as well as HaCaT as a healthy cell line, extracts from the Actinoplanes sp. produced IC₅₀ values >100 µg ml^-1 against all these lines. However, S. scabrisporus extracts produced IC₅₀ values of 0.29, 0.51 and 0.96 µg ml^-1, respectively, making this strain a very attractive model for further elucidation of its bioactive molecules. A genome mining analyses of S. scabrisporus and Actinoplanes sp. strains evidenced at least 20 and 16 clusters, respectively, of genes putatively involved in biosynthetic routes of specialized metabolites.