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Oral: 16th I.E., Melhus


Regulation of denitrification in R. solanacearum
A. TRUCHON (1), B. Dalsing (1), C. Allen (1) (1) University of Wisconsin Madison, U.S.A.

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Soil-dwelling plant pathogens need rapid metabolic adaptation to transition between the diverse micro-niches in soil and inside host plants. Tomato xylem is low in oxygen and relatively nutrient-poor, but contains around 30mM nitrate (NO3-). The bacterial wilt pathogen Ralstonia solanacearum exploits these attributes of the xylem environment by using inorganic nitrogen species as terminal electron acceptors to generate ATP via denitrification. We used a series of R. solanacearum mutants to show that the NarG – AniA – NorB – NosZ denitrification pathway is needed for virulence, contributes to NO3-respiration, and detoxification of reactive nitrogen species like nitrite (NO2-) and nitric oxide (NO) validating its important biological role. To explore this key pathway’s regulation, I mutated NorA and NorR homologs in R. solanacearum. NorA and NorR have been shown to play a role in regulation of the NO reductase NorB in R. eutropha. Preliminary results indicate that the R. solanacearum ΔnorA, ΔnorR and ΔnorAR mutants grew poorly aerobically and under denitrifying conditions. The ΔnorA, ΔnorR and ΔnorAR strains were also more susceptible to NO toxicity, accumulated more NO, and exhibited greater oxidase inhibition than wild-type R. solanacearum. These results suggest that R. solanacearum NorA and NorR may indirectly regulate denitrification by binding NO, and controlling the NO pool. Additionally NorR may directly regulate denitrification at the transcriptional level.