Isolation, identification, and biological characterization of bacterial endophytes isolated from Gunnera perpensa L.

In the present study, eleven endophytic bacterial strains, Herbaspirillum sp. (GP-SGM1, GP-SGM2, GP-SGM3, and GP-SGM11), Pseudomonas sp. (GP-SGM4, GP-SGM5), Novosphingobium sp. GP-SGM6, Chryseobacterium sp. GP-SGM7, Labedella sp. GP-SGM8, Brevibacterium sp. GP-SGM9, and Pseudomonas sp. GP-SGM10, were isolated from the rhizomes of Gunnera perpensa L. The growth kinetics, assessed through maximum growth rates (μ_max) and optical density (OD) values, revealed that GP-SGM7 exhibited highest μ_max values of 0.33 ± 0.01 hours (h)⁻¹ with an OD of 4.20 ± 0.04. In contrast, GP-SGM11 exhibited the lowest μ_max of 0.12 ± 0.05 h⁻¹ and the smallest OD of 1.50 ± 0.00. In addition, the endophyte crude extracts were tested for antibacterial activity against five pathogenic strains using the disk diffusion method, with GP-SGM7 crude extracts exhibiting promising antibacterial activity against Klebsiella pneumoniae and Staphylococcus aureus. Antioxidant activity was determined by DPPH (2, 2-diphenyl-1-picrylhydrazyl) and FRAP (ferric reducing antioxidant power) assays. The crude extracts of GP-SGM1, GP-SGM7, GP-SGM9, and GP-SGM10 were the most effective at scavenging DPPH radicals, with GP-SGM7 also exhibiting a high FRAP value of 0.54 ± 0.01. These findings emphasize the therapeutic potential of endophytic bacteria from G. perpensa L. in addressing skin-related issues, including bacterial infections and free radicals.