Characterization of endophytic bacteria associated with some medicinal plants

Document Type : Original Article


1 Central laboratory, Horticulture Research Institute, Agriculture Research Center, Giza, Egypt.

2 Department of Agricultural Microbiology, Faculty of Agriculture, Ain Shams University, Cairo, Egypt.


A total of 89 endophytic bacterial cultures were isolated by two techniques from seven medicinal plants; Coriandrum sativum, Anethum graveolens, Pelargonium graveolens, Ocimum basilicum, Rosmarinus officinalis, Saliva officinalis and Origanum majorana. To address the biological activity of these isolates as endophytic bacteria, preliminary screening showed 44, 36, 28, 22, 82 isolates out of total one gave positive results for cellulase, pectinase, amylase activities, indole acetic acid (IAA) and gibberellic acid (GA3) production, respectively. The secondary screening twenty endophytic bacterial isolates were selected and examined for their antagonistic effect against four pathogenic fungi, antioxidants activity, total phenols, indole acetic acid, ammonia (NH3), siderophores production and nitrogenase activity. According to the last screening; six isolates were chosen because of their multi-plant growth promoting (PGP) traits. They recorded a wide range of total flavonoids concentration in endophytic bacterial supernatant. The values of total flavonoids varied from 1.43 to 31.14 ppm. While the alkaloids production was detected by all tested isolates except isolate S14. Isolate B3 gave the maximum alkaloids concentration in its supernatant being 0.34 ppm. Four isolates are able to solubilize phosphate, low variations between tested isolates in phosphate solubilization ranged from 5.65 ppm by isolate RO14 to 3.85 ppm by isolate C8. All isolates showed negative result for hydrogen cyanide (HCN) production. Furthermore, the colonization of the six most efficient isolates inside the tissue of two medicinal plant Ocimum basilicum and Coriandrum sativum were performed by two techniques; 2,3,5-triphenyl tetrazolium chloride (TTC) stain and Transmission electron microscope (TEM). Based on some morphological and biochemical characteristics of the most efficient isolates (RO10, RO14, S14, D6, C8 and B3); the six isolates were similar to three genera (Enterobacter sp., Aeromonas sp. and Bacillus sp.). Hypersensitivity test proved that all the six endophytic bacterial isolates are nonpathogenic bacteria. Where, these isolates gave negative symptoms of hypersensitivity reaction (HR) test on the pepper plants (Capsicum annuum) used as indicator plant.