title: Host control over infection and proliferation of a cheater symbiont.
abstract: Host control mechanisms are thought to be critical for selecting against cheater mutants in symbiont populations. Here, we provide the first experimental test of a legume host's ability to constrain the infection and proliferation of a native-occurring rhizobial cheater. Lotus strigosus hosts were experimentally inoculated with pairs of Bradyrhizobium strains that naturally vary in symbiotic benefit, including a cheater strain that proliferates in the roots of singly infected hosts, yet provides zero growth benefits. Within co-infected hosts, the cheater exhibited lower infection rates than competing beneficial strains and grew to smaller population sizes within those nodules. In vitro assays revealed that infection-rate differences among competing strains were not caused by variation in rhizobial growth rate or interstrain toxicity. These results can explain how a rapidly growing cheater symbiont--that exhibits a massive fitness advantage in single infections--can be prevented from sweeping through a beneficial population of symbionts.
authors.affiliation: University of California, Riverside, CA 92521, USA. goran.arnqvist@ebc.uu.se
authors.forename: J L
authors.initials: JL
authors.lastname: Sachs
authors.forename: J E
authors.initials: JE
authors.lastname: Russell
authors.forename: Y E
authors.initials: YE
authors.lastname: Lii
authors.forename: K C
authors.initials: KC
authors.lastname: Black
authors.forename: G
authors.initials: G
authors.lastname: Lopez
authors.forename: A S
authors.initials: AS
authors.lastname: Patil
mesh_terms: D020369:Bradyrhizobium / Q000254:growth & development / Q000502:physiology*; D054884:Host-Pathogen Interactions; D000070116:Lotus / Q000254:growth & development / Q000382:microbiology*; D018517:Plant Roots / Q000382:microbiology; D013559:Symbiosis / Q000502:physiology*