Isolation, biochemical characterization, and antimicrobial activities of EPS-producing bacterial endophytes from Moringa oleifera.

Abstract

Bacterial endophytes are a key part of the plant microbiome that influence developmental processes via different mechanisms. One of the known mechanisms is the production of exopolysaccharides (EPS) that are responsible for the response towards stresses and plant-bacterial interactions. In the current experiment, we isolated 42 strains of bacterial endophytes from the sterilized parts of Moringa oleifera plant and screened them for the production of EPS. Out of the 42, only three isolates; KR-27, KL-4, and KS-7 produced a significant amount of EPS. All these isolates showed in vitro antagonistic activities against phytopathogenic fungi and bacteria. These antagonistic endophytic isolates, KR-27, KL-4, and KS-7 were identified as Serratia marcescens, Klebsiella aerogenes, and Lelliottia amnigena, respectively based on 16 s RNA gene ribotyping. The selected bacterial strains were screened out for phytohormones and secondary metabolites production and all the identified strains produced significant amount of various phytohormones such as indole acetic acid (IAA), gibberellic acid (GA₃), and salicylic acid (SA). In addition, the identified strains produced the antioxidant compounds like siderophores, phenolics, and flavonoids. The phosphate solubilization ability of all the strains was ascertained and found highest for KR-27 (30.46 ± 0.82 μg/mL), followed by KS-7 (18.30 ± 0.54 μg/mL) and KL-4 (17.36 ± 0.68 μg/mL). Unlike previous research, which primarily focused on the nutritional and medicinal properties of M. oleifera, this research uncovers the new aspect by exploring the biotechnologically important bacterial flora of this miracle tree. In conclusion we isolated three novel bacterial endophytic strains with the ability to produce bioactive compounds for plant and antimicrobial activity against phytopathogens for the first time which can replace the synthetic fertilizers and pesticides in future sustainable agriculture practices.