Poster: Plant-symbiont interactions
Abs #
594: Regulation of Nitrogen Metabolism in Plant-Associated Bacteria, Methylobacterium spp.
|
|
Presenter: |
Witzig, Steve B., sbw9b0@mizzou.edu |
Authors | Witzig, Steve B. (A) Polacco, Joe C. (A) | | Affiliations: |
(A): University of Missouri-Columbia
|
|
|
Pink-Pigmented Facultative Methylotrophic bacteria (PPFMs) have been found to be the most abundant microorganisms among phylloplane microflora, and have been recovered from all plants examined. PPFMs are seed-transmitted and have been shown to enhance germination. We have shown that PPFMs associated with urease-negative soybean mutants unable to insert nickel in the plant urease active site, are themselves urease-negative while on the plant and transiently urease-negative in free-living culture. Reacquisition of PPFM urease activity was accelerated by nickel supplementation. To understand how the soybean genotype affects the expression of urease in PPFMs we are determining the organization and expression of the Methylobacterium urease operon. We have constructed a single exchange crossover mutation in the structural gene ureC (ex15), which completely abolishes urease activity. Wildtype (WT) PPFMs can utilize ammonia, urea and allantoin, but not arginine or hydantoin, as sole nitrogen (N) sources. ex15 can not utilize urea or allantoin. Ureides (including allantoin) are the major form of N transported from fixing soybean nodules. PPFMs release N from allantoin as urea and this may contribute to the urea-N pool in plants. The urease activity of PPFMs grown on allantoin as the sole N source was 5-11 fold higher than in PPFMs grown on ammonia. However, cultures grown on allantoin+ammonia had only the urease activity of ammonia-grown cultures. We are investigating whether allantoin degredation in PPFMs is co-regulated with urease activity and have found that WT PPFMs do not utilize allantoin when grown in the presence of ammonia. This agrees with the urease activity data. This research focuses on furthering our understanding of the interactions between PPFMs and plants.
