PS 2-26 - Antagonistic and competitive dynamics detected in vitro between sagebrush-associated microbes

Abstract: Plant leaf surfaces host diverse communities of microbial organisms that influence plant health and function. The interactions between species of a plant’s microbiome, often via antimicrobial metabolites, impact community structure and host-microbe dynamics. These metabolites can be isolated and harnessed for biocontrol or medicinal applications. To date, no studies have investigated interactions between microbes isolated from the leaves of sagebrush (Artemisia tridentata). In this study, we selected three previously isolated microbes from sagebrush leaves to determine their interactive properties when co-cultured in vitro: Aureobasidium pullulans, Bacillus amyloliquefaciens, and Cladosporium herbarum, chosen based on known antimicrobial or phytopathogenic properties. We hypothesized that when co-cultured in vitro, these microbes would exhibit interspecific antagonistic and/or competitive behaviors. We plated six replicates of cultures containing all three species, six replicates each of three pairwise cultures, and monocultures as controls. We photographed cultures for ten days and observed morphology, growth patterns, and signs of antagonism for all microbes. Total growth in surface area of the microbial colonies was measured in ImageJ. Statistical analysis conducted in R revealed significantly inhibited growth of C. herbarum in all co-cultures when compared to the control, while A. pullulans growth was only inhibited in co-cultures with B. amyloliquefaciens, and no significant reduction in growth was found for B. amyloliquefaciens in any co-culture. We observed visible zones of inhibition in co-cultures of B. amyloliquefaciens with C. herbarum and A. pullulans with C. herbarum. Co-cultured microbes also differed in morphology when compared to controls. These results support competitive and antagonistic dynamics at play between sagebrush-associated microbes. Future analysis of metabolites produced in monocultures vs. co-cultures, including antimicrobial assays and liquid chromatography-mass spectrometry (LCMS), will serve to isolate the mechanism driving growth inhibition. Increasing our understanding of microbial interactions opens the door for myriad real-world applications in agriculture, ecosystem management, and medicine.