Hannah Anderson

Resource competition among Streptomyces in soil has been hypothesized to be a principal mechanism mediating the inhibitory capacity of soil microbial communities, but the factors that influence competitive interactions are less well-known, especially in relation to crop management. To understand how soil nutrient levels can impact microbial interactions, I compared how two contrasting long-term crop management systems affected resource utilization and inhibitory phenotypes within sympatric soil Streptomyces populations. I conducted pairwise inhibition assays between isolates of the same treatment to determine the proportion and intensity of inhibitory phenotypes between populations and used BioLog SF-P2 96-well plates to characterize nutrient use. I hypothesized that resource niche width and overlap, as well as the intensity and proportion of inhibitory phenotypes would be greater in low nutrient soil populations. Niche width and proportion of inhibitory phenotypes were not significantly different while niche overlap and inhibition intensity were greater in low than high nutrient soils, suggesting that while isolates between treatments may be able to utilize a similar number of nutrients, long-term resource competition between sympatric Streptomyces populations induced by a nutrient limiting environment could impose selection for stronger inhibitors. Future research to identify and sequence genes associated with these inhibitory phenotypes will provide additional insights into the selective trajectories leading to pathogen suppression among soil Streptomyces.