Significance of Antibiotic Production by Cephalosporium Gramineum to Its Saprophytic Survival

Of several hundred isolates of Cephalosporium gramineum from nature, all produced a wide-spectrum, antifungal antibiotic. In contrast, certain single-spore isolates from cultures maintained at 6 °C for 2–5 years on potato dextrose agar produced little or no antibiotic. This suggests that in nature a selective force acts to preserve antibiotic producers and to eliminate nonproducers.Selection pressure in favor of antibiotic producers apparently is not exerted in the parasitic phase, because both antibiotic producers and nonproducers are pathogenic. Mycelial growth rates do not give a selective advantage to antibiotic producers as they usually grow more slowly than do nonproducers. The antibiotic itself does not exert selective pressure on nonproducers since nonproducers are not inhibited in culture by producers.Antibiotic producers established in straw reduce the invasion of the straw in soil by other fungi more than do the nonproducers. These observations support the hypothesis that the antibiotic aids the survival of C. gramineum in its saprophytic phases, and that selection pressure in favor of antibiotic producers is probably exerted while the fungus is in the soil.