Rhizosphere colonization

Martmez-Granero F, S Capdevila, M Sanchez-Contreras, M Martin, R Rivilla (2005) Two site-specific recom-binases are implicated in phenotypic variation and competitive rhizosphere colonization in Pseudomonas fluorescens. Microbiology (UK) 151 975-983. 

M. Simons, A. J. van der Bij, I. Brand, L. A. de Weger, C. A. Wijffelman, and B. J. J. Lugtenberg, Gnotobiotic system for studying rhizosphere colonization by plant growth-promoting Pseudomonas bacteria. Molec. Plant Microbe Interact. 9 600 (1996). 

W. R. Streit, C. M. Joseph, and D. A. Phillips, Biotin and other water-soluble vitamins are key growth factors for alfalfa rhizosphere colonization by Rhizobium meli-loti 1021. Molec. Plant Microbe Interact. 5 330 (1996). 

E. A. Robleto, A. J. Scupham, and E. W. Triplett, Trifolitoxin production in Rhizohium eili strain CE3, increases competitiveness for rhizosphere colonization and root nodulation of pha.seolus vulgaris in soil. Mol. Plant Microbe Interact. 10 228-233 (1997). 

Martmez-Granero F, R Rivilla, M Martin (2006) Rhizosphere selection of highly motile phenotypic variants of Pseudomonas fluorescens with enhanced competitive colonization ability. Appl Environ Microbiol 72 3429-3434. 

In this chapter we review the current literature available on the influence of root exudates on rhizosphere microbial populations and the effects of plant, microbial and soil factors on the processes of rhizodeposition and microbial colonization and activity. We first give a brief overview and definitions of some of the main concepts relating to the rhizosphere and rhizodeposition. 

These data strongly suggest that siderophore production by root-colonizing microorganisms is induced only at a level neeessary to supplement that which is not provided by phytosiderophores and organic acids released during the plant iron stress response. Thus, the plant iron stress response may control iron availability to microorganisms in the rhizosphere. 

Initial studies examining the function of siderophores in the rhizosphere have focused on practical problems related to agricultural biotechnology. Early research suggested the involvement of siderophores in plant disease suppression by certain root-colonizing pseudomonads (2). Since then, it has become apparent that siderophore-mediated interactions are only part of the story of how microor-... 

XIV. ECOLOGY AT THE SPECIES LEVEL SURVIVAL AND COLONIZATION IN DIFFERENT RHIZOSPHERES AND SOILS... 

The importance of including soil-based parameters in rhizosphere simulations has been emphasized (56). Scott et al. u.sed a time-dependent exudation boundary condition and a layer model to predict how introduced bacteria would colonize the root environment from a seed-based inoculum. They explicitly included pore size distribution and matric potential as determinants of microbial growth rate and diffusion potential. Their simulations showed that the total number of bacteria in the rhizosphere and their vertical colonization were sensitive to the matric potential of the soil. Soil structure and pore size distribution was also predicted to be a key determinant of the competitive success of a genetically modified microorganism introduced into soil (57). The Scott (56) model also demonstrated that the diffusive movement of root exudates was an important factor in determining microbial abundance. Results from models that ignore the spatial nature of the rhizosphere and treat exudate concentration as a spatially averaged parameter (14) should therefore be treated with some caution. 

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