Endophytic and rhizospheric bacteria of medicinal plants as sources of bioactive compounds: Antimicrobial and antioxidant potential

Endophytes, microorganisms that inhabit internal plant tissues without causing harm, are increasingly recognized as valuable sources of bioactive metabolites with industrial, agricultural, and pharmaceutical relevance. This study aimed to isolate, identify, and evaluate the antimicrobial and antioxidant activities of endophytic and rhizospheric bacteria associated with medicinal plants from North Shewa, Ethiopia. This study hypothesized that endophytic and rhizospheric bacteria associated with medicinal plants from North Shewa, Ethiopia, produce bioactive compounds with significant antimicrobial and antioxidant potential. We hypothesized that these bacterial communities synthesize metabolites capable of inhibiting test microorganisms and scavenging free radicals. Isolation was carried out from sterilized leaves and roots, as well as from root washes, on nutrient agar at 30°C for 72h. The isolates were first screened via the perpendicular method and then via the disc diffusion method. Fermented broths were extracted via solvents. Among the 104 isolated microbes, including 89 endophytic and 15 rhizospheric microbes, 29 showed antibacterial activity. The main bioactive-producing isolates were Pseudomonas oleovorans, Ligilactobacillus salivarius, Bacillus subtilis, and Pseudomonas fluorescens. Notably, P. oleovorans was effective against Streptococcus epidermidis (13.7mm) and Staphylococcus aureus (12mm), with inhibition zones ranging from 8 to 13.7mm for all the tested organisms. The antioxidant activity ranged from 15.42% to 22.57%, with the highest value observed for P. oleovorans (22.57%). These findings highlight the potential of endophytic and rhizospheric bacteria as promising and sustainable sources of bioactive compounds.