Abstract
Endophytic actinomycetes from medicinal plants produce a wide diversity of secondary metabolites (SM). However, to date, the knowledge about endophytes from Brazil remains scarce. Thus, we analyzed the antimicrobial potential of 10 actinomycetes isolated from the medicinal plant Vochysia divergens located in the Pantanal sul-mato-grossense, an unexplored wetland in Brazil. Strains were classified as belonging to the Aeromicrobium, Actinomadura, Microbacterium, Microbispora, Micrococcus, Sphaerisporangium, Streptomyces, and Williamsia genera, through morphological and 16S rRNA phylogenetic analyzes. A susceptibility analysis demonstrated that the strains were largely resistant to the antibiotics oxacillin and nalidixic acid. Additionally, different culture media (SG and R5A), and temperatures (28 and 36°C) were evaluated to select the best culture conditions to produce the active SM. All conditions were analyzed for active metabolites, and the best antibacterial activity was observed from metabolites produced with SG medium at 36°C. The LGMB491 (close related to Aeromicrobium ponti) extract showed the highest activity against methicillin-resistant Staphylococcus aureus (MRSA), with a MIC of 0.04 mg/mL, and it was selected for SM identification. Strain LGMB491 produced 1-acetyl-β-carboline (1), indole-3-carbaldehyde (2), 3-(hydroxyacetyl)-indole (4), brevianamide F (5), and cyclo-(L-Pro-L-Phe) (6) as major compounds with antibacterial activity. In this study, we add to the knowledge about the endophytic community from the medicinal plant V. divergens and report the isolation of rare actinomycetes that produce highly active metabolites.
Highlights
Endophytes are microorganisms that inhabit the internal tissues of plants without causing any negative effects, and actinomycetes isolated from plants have been widely studied due their ability to produce active metabolites (Kim et al, 2000; Zhao et al, 2011; Kadiri et al, 2014; Golinska et al, 2015; Savi et al, 2015a,b)
In order to determine the compounds responsible for the biological activity observed for the crude extract of strain LGMB491, we evaluated the antibacterial activity of compounds 1–9 against S. aureus and methicillin-resistant S. aureus. 1-Acetyl-β-carboline (1) showed an equivalent activity as the antibiotic methicillin against S. aureus, different from this antibiotic, compound 1 showed activity against methicillin-resistant Staphylococcus aureus (MRSA) (Table 5)
Actinomycetes from medicinal plants are the source of several secondary metabolites with biological activity (Qin et al, 2015; Savi et al, 2015b), and their metabolites may be associated with the medicinal properties of the plant host (Kusari et al, 2013; Santos et al, 2015)
Summary
Endophytes are microorganisms that inhabit the internal tissues of plants without causing any negative effects, and actinomycetes isolated from plants have been widely studied due their ability to produce active metabolites (Kim et al, 2000; Zhao et al, 2011; Kadiri et al, 2014; Golinska et al, 2015; Savi et al, 2015a,b). The rare actinomycetes are an underexplored group, the use of these organisms, and their compounds have gained great importance in drug discovery programs (Rong and Huang, 2012; Tiwari and Gupta, 2012), mainly to combat infections caused by resistant microorganisms. In order to find microorganisms with potential to produce active metabolites our group has been searching endophytic microorganisms from medicinal plants located in underexplored environments, such as the Brazilian wetland regions (Savi et al, 2015a,b; Hokama et al, 2016; Peña et al, 2016; Santos et al, 2016; Tonial et al, 2017). The focus of this study is to identify endophytic actinomycetes from the medicinal plant V. divergens and to assay their secondary metabolites, dependent on different culture conditions, against clinical pathogens associated with antibiotic resistance
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