Linking Culture Chemistry To Isolation Success And Microbial Inhibition Potential Of Microbial Symbionts From Laurus Nobilis

The growing problem of antibiotic resistance has led researchers to look to plants as potential sources of antibiotics. Antibiotic activity in plants may represent the plant’s own products or products of its foliar microbiome, including endophytes (microbes that live within healthy plant tissue). Medicinal plants are especially interesting as potential sources of endophytes with antimicrobial activity. This study sought to determine whether endophytes that occur within leaves of Laurus nobilis (common bay leaf) have antimicrobial activity. Here, diverse microbiological media were used to isolate endophytes from individuals of L. nobilis on the University of Arizona campus. Endophytes were then identified via molecular barcoding, and representative strains (Bacillus megaterium, Aspergillus tubigensis, and Brevibacterium frigoritolerans) were chosen for antimicrobial assays against a panel of test organisms (Candida albicans, Escherichia coli, Bacillus subtilis, Amycolatopsis sp. AA4). Endophyte isolates showed no inhibition of three test organisms, but all three endophytes inhibited Amycolatopsis sp. AA4 in Trial 1. This inhibition could not be replicated in subsequent trials. All three endophytes are known to produce silver nanoparticles, to which species of the Amycolatopsis genus are susceptible. This study suggests the potential for some endophytes of L. nobilis to have antimicrobial activity worthy of future exploration