Plant Endophytes as Novel Sources of Antimicrobials: Characterizing Fungal Isolates from Alfalfa

Microbial antibiotic resistance is increasing at alarming rates, posing a critical need for new sources of antibiotics. Many forms of antibiotics currently in use were developed from fungal species which produce antimicrobial compounds to ward off microbial competitors. Fungal species known as endophytes live symbiotically within plants and may exhibit these characteristics. This is of particular importance in agriculture, as fungal endophytes may protect plants against disease and increase crop yield. Our research goal was to identify endophytes present in alfalfa, and if they produce antimicrobials. We obtained alfalfa crop samples grown in Minnesota and Idaho, cultured and isolated fungal endophytes from alfalfa stem tissue, and discovered isolate identity using 18S ribosomal subunit gene sequence. We evaluated isolate antimicrobial potential by cross-streaking isolates with a number of test bacterial and fungal strains, including known alfalfa pathogens, and disk-diffusion assays using compounds extracted from isolates to measure growth inhibition. We identified over 45 isolates successfully, representing both alfalfa pathogens and endophytes, and at least 10 isolates produce possible antimicrobial substances that inhibit bacterial and fungal species. These fungal endophytes and the antimicrobials they produce may play a role in protecting alfalfa from disease, and the antimicrobial compounds could be potentially used in clinical research. Alfalfa, along with other plant species, need to be considered as likely sources for novel antimicrobials.