Predator prey and the third beneficiary

All bacterial epibiotic predators are rich in secondary metabolites and most genera rich in secondary metabolites have demonstrable predatory abilities. Therefore it is likely that an antibiotic resistant and thereby predation resistant species may benefit not only by escaping predation but also by utilizing nutrients released by lysis of prey cells by predatory bacteria. The resistant organisms may enjoy greater fitness benefits than the predator since they get the benefit without investing in the predation machinery. In our experiment, a marine isolate of Streptomyces atrovirens showed good predatory activity on a range of species including Staphylococcus aureus and Proteus vulgaris. Escherichia coli was resistant to predation by this species. On slide culture with water agar when the predator, S. aureus and E. coli were grown together S. aureus population declined whereas the predation resistant E. coli increased their population as compared to controls. However the growth of E. coli did not affect growth of the predator unfavorably. This strengthens the possibility that evolution of antibiotic resistance not only gave a selective advantage of escaping predation, it also would have increased the fitness of the resistant organism by promoting growth on nutrients released from the prey cells lysed by the predator. When the predator was grown with S. aureus and P. vulgaris as prey, S. aureus declined rapidly whereas P. vulgaris was spared. This suggests that the predator appears to show preference towards prey and in that case even a partial or relative resistance may give substantial advantage to a population.