title: Oscillatory dynamics in a bacterial cross-protection mutualism.
abstract: Cooperation between microbes can enable microbial communities to survive in harsh environments. Enzymatic deactivation of antibiotics, a common mechanism of antibiotic resistance in bacteria, is a cooperative behavior that can allow resistant cells to protect sensitive cells from antibiotics. Understanding how bacterial populations survive antibiotic exposure is important both clinically and ecologically, yet the implications of cooperative antibiotic deactivation on the population and evolutionary dynamics remain poorly understood, particularly in the presence of more than one antibiotic. Here, we show that two Escherichia coli strains can form an effective cross-protection mutualism, protecting each other in the presence of two antibiotics (ampicillin and chloramphenicol) so that the coculture can survive in antibiotic concentrations that inhibit growth of either strain alone. Moreover, we find that daily dilutions of the coculture lead to large oscillations in the relative abundance of the two strains, with the ratio of abundances varying by nearly four orders of magnitude over the course of the 3-day period of the oscillation. At modest antibiotic concentrations, the mutualistic behavior enables long-term survival of the oscillating populations; however, at higher antibiotic concentrations, the oscillations destabilize the population, eventually leading to collapse. The two strains form a successful cross-protection mutualism without a period of coevolution, suggesting that similar mutualisms may arise during antibiotic treatment and in natural environments such as the soil.
authors.affiliation: Physics of Living Systems, Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139.
authors.forename: Eugene Anatoly
authors.initials: EA
authors.lastname: Yurtsev
authors.affiliation: Physics of Living Systems, Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139.
authors.forename: Arolyn
authors.initials: A
authors.lastname: Conwill
authors.affiliation: Physics of Living Systems, Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139 gore@mit.edu.
authors.forename: Jeff
authors.initials: J
authors.lastname: Gore
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects*; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D018407:Bacterial Physiological Phenomena / Q000187:drug effects; D018920:Coculture Techniques; D056738:Cross Protection / Q000187:drug effects*; D004352:Drug Resistance, Microbial; D004926:Escherichia coli / Q000145:classification / Q000187:drug effects / Q000254:growth & development*; D056265:Microbial Interactions / Q000187:drug effects*; D013559:Symbiosis / Q000187:drug effects*
chemical_list: D000900:Anti-Bacterial Agents
keywords: antibiotic resistance; cooperation; mutualism; oscillations; population dynamics