Antibiotic Producers in the Rhizosphere at SFSU: Antibiotic Activity and Plant Proximity
Phway Phway Myat, Lykourgos A. Tsangaropoulos
Department of Biology
Faculty Supervisor: Brinda Govindan
Soil and plants are home to diverse microbial communities that coexist or compete for survival. Secondary metabolites of certain microbes act as antimicrobial agents, giving them a selective advantage. Metabolite extractions, known as antibiotics, inhibit the cellular processes of target pathogens, thereby preventing infections (Raaijmakers & Mazzola, 2012). Since both soil and plant microbes show antibiotic properties, the proximity of the soil to plants posed a question on the effectiveness of soil antibiotic producers. It was hypothesized that the closer the soil to the plant, the greater antibiotic properties soil microbes have. However, this study at SFSU found that two soil bacterial isolates away from the plants inhibited Staphylococcus epidermidis with 9-mm and 11-mm zones. One isolate near the plants inhibited mold, not the tester bacteria, with a 6-mm zone. An additional isolate from a “near plant” culture plate formed 19-mm inhibition around S. epidermidis. The hypothesis was rejected by finding more antimicrobial bacteria with larger zones from “away from plant” samples. Keywords: antibiotic properties, soil, plants, rhizosphere, Streptomyces, Exiguobacterium, Pseudomonas, zone of inhibition, master plate, isolates, bacterial lawns