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, <i>Hypericum perforatum</i> and <i>Ziziphora capitata</i> 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 <i>H. perforatum</i> exhibited a remarkable activity against bacterial and fungal pathogens, whereas extracts of <i>Z. capitata</i> 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 <i>H. perforatum</i> belong to eight genera (<i>Arthrobacter, Achromobacter, Bacillus, Enterobacter, Erwinia, Pseudomonas, Pantoea, Serratia</i>, and <i>Stenotrophomonas</i>). The endophytic isolates from <i>Z. capitata</i> also contain those genera except <i>Arthrobacter</i>, <i>Serratia</i>, and <i>Stenotrophomonas</i>. <i>H. perforatum</i> with antibacterial activity supported more bacteria with antagonistic activity, as compared to <i>Z. capitata</i>. The antagonistic isolates were able to control tomato root rot caused by <i>Fusarium oxysporum</i> and stimulated plant growth under greenhouse conditions and could thus be a cost-effective source for agro-based biological control agents.