Endophytes from medicinal plants’ seeds: exploring new reservoirs of bioactive molecules

Plant-associated microorganisms have recently gained more attention for their influence on plant health and biotechnological relevance. Bioactive molecules have been already isolated from plant-associated bacteria. Seed-borne bacterial endophytes have not been much explored though. Such endophytes are particularly important, since they can influence germination and be transmitted from generation to generation. Interestingly, seed endophytes from medicinal plants could influence the production of molecules with therapeutic properties. Bacterial endophytic strains were extracted from surface-sterilized seeds of the medicinal plant Echinacea purpurea and their 16S rRNA genes were sequenced. The analysis revealed the predominance of Paenibacillus (55.8%) and Pantoea (39.5%) genera among isolates. Fluorescence in situ hybridization and confocal laser scanning microscopy (FISH–CLSM) revealed a consistent colonization of Echinacea seeds by microbial endophytes as well as epiphytes. Resistance to antibiotics revealed that Ciprofloxacin and Rifampicin are the most effective antibiotics, even at minimum concentrations (respectively 0.5 and 5 mg/l). Isolates were less sensitive to Tetracycline and Streptomycin instead. Further investigation of Echinacea plants seed-borne endophytes may elucidate how such endophytes influence the therapeutic properties of the plant, and pave the way for the discovery of biotechnologically relevant compounds.