Antimicrobial Activity of Medicinal Plants Correlates with the Proportion of Antagonistic Endophytes

Abstract

Medicinal plants are known to harbor potential endophytic microbes, due to their bioactive compounds. In a first study of ongoing research, endophytic bacteria were isolated from two medicinal plants, Hypericum perforatum and Ziziphora capitata with contrasting antimicrobial activities from the Chatkal Biosphere Reserve of Uzbekistan, and their plant-specific traits involved in biocontrol and plant growth promotion were evaluated. Plant extracts of H. perforatum exhibited a remarkable activity against bacterial and fungal pathogens, whereas extracts of Z. capitata did not exhibit any potential antimicrobial activity. Matrix-assisted laser desorption ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS) was used to identify plant associated culturable endophytic bacteria. The isolated culturable endophytes associated with H. perforatum belong to eight genera (Arthrobacter, Achromobacter, Bacillus, Enterobacter, Erwinia, Pseudomonas, Pantoea, Serratia, and Stenotrophomonas). The endophytic isolates from Z. capitata also contain those genera except Arthrobacter, Serratia, and Stenotrophomonas. H. perforatum with antibacterial activity supported more bacteria with antagonistic activity, as compared to Z. capitata. The antagonistic isolates were able to control tomato root rot caused by Fusarium oxysporum and stimulated plant growth under greenhouse conditions and could thus be a cost-effective source for agro-based biological control agents.

Keywords: Hypericum perforatum; Ziziphora capitata; antagonism; antimicrobial activity; endophytic bacteria; plant growth traits.

FIGURE 1

Antagonistic activity of endophytic bacterial isolates. (a) Pseudomonas pseudoalcaligenes S24, (b) Stenotrophomonas sp. S9 isolated from Hypericum perforatum, and (c) Enterobacter sp. M17 isolated from Ziziphora capitata against Fusarium culmorum and Fusarium oxysporum.

FIGURE 2

Control of tomato foot and root rot caused by F. oxysporum by selected antagonistic endophytic bacteria (Arthrobacter crystallopoietes S1, Achromobacter piechaudii S7, Achromobacter spanius S23, Bacillus sp. S2, Bacillus cereus S40, Pseudomonas putida S19, Pseudomonas thivervalensis S5, Pseudomonas koreensis S25, P. pseudoalcaligenes S24, Serratia liquefaciens S26, Stenotrophomonas sp. S9, A. spanius M8, Pantoea agglomerans M13). DC- disease control (soil infested with F. oxysporum spores), healthy control (no F. oxysporum spores added to the soil) had only 2% diseased plants. Column means marked by different letters indicate significant differences based on Turkey’s HSD test at P < 0.05.

FIGURE 3

The effect of seedling inoculation with selected antagonist endophytic isolates on the dry weight of tomato (A. crystallopoietes S1, A. piechaudii S7, A. spanius S23, Bacillus sp. S2, B. cereus S40, P. putida S19, P. thivervalensis S5, P. koreensis S25, P. pseudoalcaligenes S24, S. liquefaciens S26, Stenotrophomonas sp. S9, A. spanius M8, P. agglomerans M13). Column means marked by different letters indicate significant differences based on Turkey’s HSD test at P < 0.05.