| Ralstonia solanacearum, a Betaproteobacterium, causes bacterial wilt disease on hundreds of plant species. Pathogenic success of R. solanacearum is likely supported by diverse metabolic capacity, though it is not known what nutrients support its growth, survival, and virulence in the host. Genomic, transcriptomic, and metabolic analyses suggest that inorganic nitrogen may be important to R. solanacearum during infection. Here, I describe our investigations into the roles of nitrate, nitrite, nitric oxide, and nitrous oxide in R. solanacearum pathogenesis.;During infection of tomato plant xylem vessels, R. solanacearum encounters high levels of nitrate and low levels of oxygen, which support both assimilatory and respiratory nitrate consumption. Nitrate assimilation supports wild-type extracellular polysaccharide (EPS) production, root attachment, virulence on tomato following soil soak inoculation, and xylem colonization. Nitrate respiration and denitrification support ATP production, growth, virulence, and detoxification of reactive nitrogen species (RNS) during infection. RNS (nitrite and nitric oxide) are produced as a consequence of nitrate respiration and denitrification. These RNS are toxic to R. solanacearum at high concentrations when detoxification systems are disrupted. Although RNS are often produced by hosts to kill invading microbes, in the R. solanacearum-tomato plant interaction the largest contributor of RNS is the pathogen. Typically RNS are thought of as beneficial solely to the host. Here, I propose a beneficial role of RNS for R. solanacearum. My data suggest that like the host, R. solanacearum uses RNS as a signaling molecule important for its pathogenic interaction with plants. Additionally, I describe variations of inorganic nitrogen metabolic processes within the R. solanacearum species complex, which may have been shaped long ago by exposure to different environmental pressures. Furthermore, I describe my initial investigations into the roles of EPS in nitric oxide diffusion, inorganic nitrogen-mediated motility and biofilm development, and the regulatory interactions between each step of denitrification. Collectively, the work in this dissertation supports the hypothesis that inorganic nitrogen plays diverse roles in the R. solanacearum-plant interactions and deserves further dissection. |
