Diversity of disease-supportive respiratory metabolism among phylotypes of Ralstonia solanacearum
B. DALSING (1), B. McDonald (1), D. Khokhani (1), J. Klassen (2), F. Ailloud (3), E. Gonzalez-Orta (4), A. MacIntyre (1), P. Prior (5), C. Allen (6) (1) University of Wisconsin-Madison, U.S.A.; (2) University of Connecticut, U.S.A.; (3) Cirad, France; (4) Sacramento State, U.S.A.; (5) INRA, France; (6) University of Wisconsin-Madison, U.S.A.

Bacteria in the Ralstonia solanacearum species complex (RSSC) infect the xylem of diverse plant hosts, causing bacterial wilt disease. The RSSC contains four phylogenetically distinct clusters, phylotypes I-IV. We previously demonstrated that phyl. I strains can reduce nitrate to dinitrogen via complete denitrification. This four-step conversion allows inorganic nitrogen species to be used as terminal electron acceptors, supporting continued metabolic flow and growth in oxygen-limited environments like plant xylem during infection. We characterized the roles of the first three steps of this pathway in one phyl. I strain (GMI1000) in planta and in culture. We found that nitrate, nitrite, and nitric oxide reduction clearly contributed to virulence-supportive growth following direct xylem introduction. Here, we present data that suggests the last step of this pathway, the NosZ-dependent reduction of nitrous oxide to dinitrogen, is needed in phyl. I and III for full virulence in a natural infection model. We assessed denitrification metabolism in representatives of each phylotype that are equally virulent on tomato and discovered that phyl. II and IV were completely incapable of nitrous oxide reduction. Further, phyl. II and IV did not benefit from any step of denitrification even under anaerobic conditions. Taken together, our bioinformatic and experimental analyses indicate that the oxygen preferences and energy metabolism strategies of phyl. I and III are quite distinct from those of phyl. II and IV. This evolutionary divergence is striking because the macroscopic bacterial wilt disease caused by all four phylotypes is indistinguishable.

Abstract Number: P7-165
Session Type: Poster