Surface Polysaccharides as Fitness factors of Rhizospheric Nitrogen-fixing Bacteria
Elizaveta Krol and Anke Becker
from: Bacterial Polysaccharides: Current Innovations and Future Trends (Edited by: Matthias Ullrich). Caister Academic Press, U.K. (2009)
Nitrogen-fixing plant-associated bacteria include rhizospheric bacteria, endophytic diazotrophs and rhizobia, the symbiotic root nodule bacteria. Surface polysaccharides produced by bacteria contribute to their survival in the rhizosphere by improvement of the soil structure, enhancement of cell aggregation, and protection against harmful substances. Attachment of bacteria to plant roots and soil particles, which is important for colonisation of rhizosphere and roots and for infection of the plant, can be mediated by exopolysaccharides. Symbiotic interactions between root nodule bacteria and leguminous plants include infection of root tissues by bacteria and formation of nitrogen-fixing nodules, where bacteria differentiate into intracellular bacteroids. During early stages of the symbiotic interaction, exopolysaccharides, capsular polysaccharides or lipopolysaccharides can be involved in recognition by the plant and suppression of the immune response. At the stage of intracellular infection, lipopolysaccharides play an important role in maintenance of the bacteroids. Biosynthesis of surface polysaccharides is tightly regulated during both free-living growth and symbiotic development. Two-component regulatory systems, general stress response mechanisms, quorum sensing and symbiotic regulators constitute a flexible network for fine-tuning of surface polysaccharide production. In this chapter, we will focus on the structure of surface polysaccharides, produced by nodule bacteria, mechanisms of genetic regulation of their biosynthesis and their functions as fitness factors for free-living survival and symbiosis with a plant read more ...