Investigating the Effect of Soil Origin on Antibiotic Production in Streptomyces

Streptomyces bacteria produce antibiotics that inhibit competing microorganisms. We hypothesized that Streptomyces from the rhizosphere (around plant roots) would be more likely to produce antibiotics than those from bulk soil (further away from roots). Soil samples were collected from rhizosphere and bulk soils in transitional and long-term organic fields of corn and alfalfa. Streptomyces from these soils were cultured on glucose-asparagine agar media. Their antibiotic production was evaluated by testing whether they could inhibit the growth of two target Streptomyces strains. No significant effects of soil type (rhizosphere vs. bulk), crop, or management on antibiotic production were observed for one target strain. In contrast, the other target strain showed a complex interaction, where antibiotic production depended on the combination of soil type, crop, and management. The results did not support the hypothesis that rhizosphere-derived Streptomyces are more likely to produce antibiotics.