Landscape-scale Variation in Pathogen-suppressive bacteria in tropical dry forest soils of Costa Rica

Bacteria in the genus Streptomyces are ubiquitous in soil and are well-known for their production of diverse secondary metabolites, including antibiotics that can inhibit soil-borne plant pathogens and suppress disease. Pathogen-suppressive soil bacteria have the potential to influence plant community composition and diversity, but remain relatively unexplored in tropical forest soils. To estimate the potential for disease suppression among Streptomyces communities in tropical dry forests, we cultured soil-borne Streptomyces from plots in two forests in northwestern Costa Rica (Santa Rosa and Palo Verde) and quantified antibiotic-mediated pathogen inhibition against three plant pathogens. The potential for pathogen inhibition and disease suppression by Streptomyces was highly variable across the landscape. Densities of pathogen-suppressive Streptomyces varied by over ten-fold and were correlated with soil nutrients across the plots. In particular, Streptomyces communities became more pathogen-suppressive as labile soil P decreased. Inhibitor densities were significantly higher in Santa Rosa than Palo Verde, which may be related to differences in soil texture and/or plant community composition between the two forests. Our findings suggest potential differences in the degree and specificity of antibiotic-mediated disease suppression in tropical dry forest soils of Costa Rica, and highlight the need for further studies on the drivers of pathogen-suppressive phenotypes as well as the consequences of spatially variable pathogen inhibition for plant community composition in tropical forest ecosystems.