Host control over infection and proliferation of a cheater symbiont.
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.
Sachs
J L
JL
University of California, Riverside, CA 92521, USA. goran.arnqvist@ebc.uu.se
Russell
J E
JE
Lii
Y E
YE
Black
K C
KC
Lopez
G
G
Patil
A S
AS
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*