Xylella fastidiosa (Xf) is a bacterium that causes devastating plant diseases in crops such as grapes, citrus, peaches and blueberries. The goal of this project is to understand the progression and treatment of xylem fouling by bacterial biofilms formed by the plant pathogen Xf using tightly coupled theoretical and experimental techniques. The core mathematical model developed for the project uses a multiphase approach that is a flexible framework accounting for the complex interactions occurring during the disease progression. Multiphase modeling is a natural framework to account for the dramatic variation in scales (from the bacterial scale to the channel length scale). The transfer of material from free-swimming bacteria to biofilm-bound bacteria and the production of biomass (bacteria and extra-cellular polymeric 'glue') requires a distinction between the types of material within the system. Finally, multiphase models are essentially statements of conservation laws providing a relatively simple method for incorporating physical and chemical processes. Experimentally, the use of microfluidics for studies of specific behaviors of bacterial cells is recognized as a useful tool for new discoveries. Studies on single bacterial cells under controlled conditions are leading to new understandings of bacterial growth and relationship with the. Microfluidic chambers have been developed by De La Fuente's lab as a new technological approach to study the infection process of vascular plant bacterial pathogens.
The particular objectives are to determine whether the dominant symptoms of the plant infection, such as leaf scorch, are due to reduced water flux caused by occlusion of the water transport network by the biofilm or whether active plant responses are also implicated. Further, the investigation will focus on non-destructive methods of treatment of the disease. These two objectives provide fundamental insight into the disease process and treatment. The collaboration between the theoretical (mathematics) and experimental (biological) methods are used to validate the mathematical theory and suggest new avenues of disease treatment. The project initially uses experimental data to validate the theoretical modeling. In turn, the modeling and analysis is used to test various hypotheses on the disease development (e.g. occlusion versus plant responses) that are difficult to test in the laboratory. In addition, the theoretical predictions point to particular experimental designs (e.g. treatment regimes) that may provide valuable insight into non-destructive disease treatment.