A pan-genomic perspective on microbial symbiont invasions
S. PORTER (1), J. Faber-Hammond (1), M. Friesen (2) (1) Washington State University, Vancouver, U.S.A.; (2) Michigan State University, U.S.A.

Exotic, invasive plants can wreak havoc on ecosystems by displacing natives and altering environmental conditions. However, much less is known about the identities or evolutionary dynamics of the symbiotic microbes that accompany invasive plants. Nodulating leguminous plants rely upon their symbiotic rhizobium bacteria to fix nitrogen, and are incapable of colonizing areas devoid of compatible rhizobia. The invasion of the legume, Medicago polymorpha, into North America required the co-invasion of the compatible rhizobium symbiont, Ensifer medicae. We investigate whether the symbiont, E. medicae, has undergone major genomic shifts during invasion by comparing draft genome sequences of 17 of these symbionts from across their native range to 17 symbionts present in an invaded area of California. Despite hundreds of years of divergent selection in the native and invaded range, the genomes of native and invaded range rhizobia displayed remarkable overall similarity in gene content, and the vast majority of genomic diversity present across the native range appears in California. Strains from the native and Californian portions of the range differ however, in that Californian strains contain more accessory genes than native range strains. Many of these private accessory genes are involved in binding functions, transposition, recombination, and conjugal transfer. This could indicate these unique genes facilitate invasion of the symbiont by introducing novel genetic variation.

Abstract Number: P2-46
Session Type: Poster