Antibiotic production by an endophytic Streptomyces isolated from the medicinal plant Poikilospermum suaveolens

This study investigates the antibiotic production potential of endophytic actinomycetes isolated from Poikilospermum suaveolensplants. Samples were collected from various parts of the plant in karst ecosystems. Endophytic actinomycetes were cultured and screened for antimicrobial activity using agar diffusion and liquid microdilution methods. One of the 11 isolated strains exhibited significant antibiotic activity against clinically relevant organisms identified as belonging to the Streptomycesgenus, specifically Streptomyces mirabilisstrain NRRL ISP-5169. Submerged fermentation of this strain over 9 days showed strong antagonistic effects against Gram-positive bacteria. Spectroscopic analyses confirmed the presence of actinomycin D as the bioactive compound. This study provides on the previously unexplored potential of endophytic actinomycetes from P. suaveolensas a promising resource for antibiotic discovery.Keywords: Actinomycin, antimicrobial,Poikilospermum suaveolens, Streptomyces-endophyticINTRODUCTIONActinomycetes, Gram-positive bacteria with filamentous growth and high G+C DNA content, are found ubiquitously in air, terrestrial, and aquatic habitats(Barkaet al. 2015). Particularly, the genus Streptomycesis renowned for producing the majority of known microbial antibiotics (de Lima Procópio et al. 2012). This species synthesis of a wide array of biologically active metabolites, including antitumor, immunomodulatory, hypercholesterolemic, antiparasitic, insecticidal, and anti-inflammatory compounds (Al-Ansari et al. 2019; Quinn et al. 2020; Selim et al. 2021). In clinical practice, Streptomycescontribute to nearly 75-80% of these compounds (Carvalho et al. 2016; Crnovčić et al. 2013)Moreover, it was previously reported that exploring actinomycetes produces novel bioactive metabolites for clinical utilization has had restricted success, and repeated isolation of known compounds has become a foremost challenge (Qin et al. 2009). Numerous investigations have focused particularly on endophytic actinomycete within medicinal plants and the biotechnological utilization of these microorganisms (Janardhanet al. 2014). Endophytes are currently relevant in the biotechnology and industrial fields due to their ability to generate secondary metabolites as antimicrobial, biocontrol, immunosuppressant, and antitumor agents (Goudaet al. 2016). Furthermore, they also play a role in natural antioxidants, antibiotics, antidiabetic agents, and insecticidal product development (Yadav et al. 2018). These reports show actinomycetes, including medicinal plant isolates, are a potential source of new antimicrobial metabolites (Passariet al. 2015). According to previous studies, several actinomycetes are able to form intimate relations with plants and consequently colonize the inner tissues. Almost all plants have been discovered to experience infestation from one or more endophytes (Qinet al. 2009;Golinskaet al. 2015). As previously reported, actinomycetes isolated from medicinal plants have been identified as sources of many secondary biologically active metabolites (Gos et al. 2017; Savi et al. 2015); these metabolites are potentially associated with the medicinal activities of the host plants (Saini et al. 2016). However, there have been no reports on endophytic actinomycetes isolated fromPoikilospermum suaveolens.In this study, the endophytic actinomycetes isolated from a medicinal plant, P. suaveolens, analyzed the profile of metabolites of endophytic actinomycetes and purified a bioactive compound against clinical pathogens.