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

Abstract

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 (μmax) and optical density (OD) values, revealed that GP-SGM7 exhibited highest μmax values of 0.33 ± 0.01 hours (h)-1 with an OD of 4.20 ± 0.04. In contrast, GP-SGM11 exhibited the lowest μmax 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.

Keywords: Gunnera perpensa L; antibacterial activity; antioxidant activity; bacterial endophytes; bioactive compounds; growth kinetics.

Figure 1.

The maximum likelihood phylogenetic tree based on the 16S rRNA gene sequences showing the relationship between 11 bacterial endophytes of this study and related species. The phylogenetic analysis was constructed with MEGA version 11.0 using the neighbor-joining method (bootstrap value set at 1000 replicates) (Biderre-Petit et al. 2016). The Interactive Tree of Life (iTOL) platform was used to design the tree layout (Myer et al. 2020). Specific colors were used to mark each genus: Herbaspirillum (green), Novosphingobium (blue), Brevibacterium (red), Labedella (orange), Chryseobacterium (yellow), and Pseudomonas (purple), and AB269763 Escherichia coli strain AE1-2 was used as an outgroup.

Figure 2.

Scanning electron microscopy analysis of endophytic bacteria isolated from G. perpensa L. viewed at 50.0 kx magnification: (A) Herbaspirillum sp. strain GP-SGM1, (B) Herbaspirillum sp. strain GP-SGM2, (C) Herbaspirillum sp. strain GP-SGM3, (D) Pseudomonas sp. strain GP-SGM4, (E) Pseudomonas sp. strain GP-SGM5, (F) Novosphingobium sp. strain GP-SGM6, (G) Chryseobacterium sp. strain GP-SGM7, (H) Labedella sp. strain GP-SGM8, (I) Brevibacterium sp. strain GP-SGM9, (J) Pseudomonas sp. strain GP-SGM10, and (K) Herbaspirillum sp. strain GP-SGM11.

Figure 3.

Ferric reducing antioxidant power assay of G. perpensa L. endophytic crude extracts (n = 3). (A) Ascorbic acid (), where GP-SGM1 (): Herbaspirillum sp. strain GP-SGM1, GP-SGM2 (): Herbaspirillum sp. strain GP-SGM2, GP-SGM3 (): Herbaspirillum sp. strain GP- SGM3; (B) GP-SGM4 (): Pseudomonas sp. strain GP-SGM4, GP-SGM5 (): Pseudomonas sp. strain GP-SGM5, GP-SGM6 (): Novosphingobium sp. strain GP-SGM6, GP-SGM7 () Chryseobacterium sp. strain GP-SGM7; (C) GP-SGM8 (): Labedella sp. strain GP-SGM8, GP-SGM9 (): Brevibacterium sp. strain GP-SGM9, GP-SGM10 (): Pseudomonas sp. strain GP-SGM10, GP-SGM11 (+): Herbaspirillum sp. strain GP-SGM11. Data were presented as average ± SD of triplicates.