Rhizobium adapts lifestyles from rhizosphere to symbiosis

Rhizobia are soil-dwelling bacteria that form symbioses with legumes and provide biologically useable nitrogen as ammonium for the host plant. During symbiosis, rhizobia must adapt to several different lifestyles. These range from free-living growth in the rhizosphere, through root attachment and colonization, to passage along infection threads, differentiation into bacteroids that fix N2, and, finally, bacterial release from nodules at senescence.