EXPERIMENTAL STUDIES ON THE ECOLOGICAL ROLE OF ANTIBIOTIC PRODUCTION IN BACTERIA

Genetically well-characterized strains of antibiotic-producing soil ba cteria (Streptomyces griseus and Streptomyces coelicolor) were used to examine the ecological role of antibiotic production. Streptomycetes were competed against sensitive and resistant Bacillus subtilis, anoth er soil bacterium, on surface (agar) culture. The ecological role of a ntibiotics was examined in three levels of competition. (1) Capacity o f antibiotics to allow invasion of producing organisms (B. subtilis es tablished and streptomycetes added later). (2) Capacity of antibiotics to mediate competition between established populations (B. subtilis a nd streptomycetes co-inoculated). (3) Capacity of antibiotics to preve nt invasion by competitors (streptomycetes established and B. subtilis added later). Antibiotic production was found to play a significant r ole in preventing the invasion of competitors in these experiments. An tibiotic production did not improve the ability of producers to invade a population of sensitive cells nor did it play a strong role in medi ating competition between established populations. Antibiotic producti on also selected for antibiotic-resistant bacteria among invading comp etitors.