Spatial variability in nutrient utilization of Streptomyces from prairie soil

Streptomyces are bacterial saprophytes that are ubiquitous in soil and noted for their capacity to produce a diverse variety of antibiotics. Although antibiotics are hypothesized to be important to competitive fitness (interference competition), there has been little effort to document potential alternative competitive strategies, including nutrient specialization, used by Streptomyces in natural habitats. We examined spatial variation in nutrient utilization among Streptomyces isolates from 3 locations from prarie soils at Cedar Creek Natural History Area in east-central Minnesota using BIOLOG^® plates. Among the 152 isolates examined, nutrient use varied widely (39-95 nutrients used per isolate; mean = 78.0). Seven nutrients were used by all isolates, while L-alanine was used by only 23 of the 152 isolates. Location 1 supported the highest frequency of generalists, while location 3 supported the greatest proportion of specialists. The frequency of specialists was inversely correlated with mean inhibitory activity within the community, suggesting distinct competitive strategies among Streptomyces isolates within different communities. Specifically, in location 1, interference competition predominated among the collection of generalist Streptomyces, while location 3 supported nutrient specialists that were significantly less inhibitory. These results support the significance of competitive interactions in structuring soil microbial communities, and suggest that competitive strategies may vary substantially among Streptomyces communities in different locations in soil.