Sara Saleh, “Motility is Important for Competitive Nodulation of Mimosa pudica by Paraburkholderia phymatum”
Mentors: Gyaneshwar Prasad & Shashini Welmillage, Biological Sciences
Nitrogen (N) is the most limiting nutrient for plants and plant growth requires supplementation with N-fertilizer that results in environmental degradation. However, many bacteria can fix atmospheric nitrogen and some plants, such as legumes, form a symbiotic relationship with N-fixing bacteria, giving them a richer, more steady supply of nitrogen than most other plants. The mechanisms important for the rhizobial-legume symbiosis are extensively studied. However, these studies have been performed in sterile and well-defined conditions in the laboratory. In contrast, very little is known about the mechanisms that mediate rhizobial-legume symbiosis in natural soils that contain many other microorganisms. To study legume nodulation in soils, we are utilizing the symbiosis between Mimosa pudica and Paraburkholderia phymatum. M. pudica is native to Brazil and the soils of Midwestern USA lack P. phymatum. Random transposon insertion mutants in P. pymatum were screened for defects in motility as compared to the wild type strain. A total of two mutants that were significantly less motile than the wild type were selected and evaluated for their ability to nodulate M. pudica. All mutants were able to nodulate M. pudica similar to the wild type in both axenic and soil conditions. These results indicate that motility is not required for nodulation. To determine if motility can confer competitive advantage, the mutants were co-inoculated with the wild type strain in different ratios and their nodulation ability was determined by reisolating mutants from the nodules. In contrast to the results with individual inoculation, the mutants showed significant defect in symbiosis when co-inoculated with the wild type. Only ~25% of the nodules contained the mutants. These results show that rhizobial motility is not essential but is required for competitive ability of these bacteria to colonize their legume host.
Click the thumbnail below to open the full sized poster in a new tab.