Rhizosphere

A recent suggestion has been to use plants to stimulate the microbial degradation of the hydrocarbon (hydrocarbon phytoremediation). This has yet to receive clear experimental verification, but the plants are proposed to help deUver air to the soil microbes, and to stimulate microbial growth in the rhizosphere by the release of nutrients from the roots. The esthetic appeal of an active phytoremediation project can be very great. 

It is a general observation that herbicide degradation occurs more readily ia cultivated than fallow sod, suggesting that rhizosphere organisms are effective herbicide degraders. Whether this can be effectively exploited ia a phytoremediatioa strategy remains to be seea. 

It will also be important to understand the rhizosphere ecology around the roots of metal accumulating plants fully. Maximizing the bioavailabihty of the contaminant metals in this zone may require the optimization of the microbial communities, or perhaps the addition of soil amendments. There are early indications that such intervention may be beneficial (88), but research in this area is at a very early stage. 

Walton BT, Anderson TA. 1990. Microbial degradation of trichloroethylene in the rhizosphere Potential application to biological remediation of waste sites. Appl Environ Microbiol 56 1012-1016. 

LMG10653 (KBC 1) wild type strain, isolated from roots and rhizosphere of rice (Iraq) Khammas e/o/., 1989... 

Establishment of inoculated Azospirillum spp. in the rhizosphere and in roots of field grown wheat and sorghum. Plant Soil 90 35-46. 

Khammas, K. M., Ageron, E., Grimont, P A D. and Kaiser, P., 1989. Azospirillum irakense sp. nov., a nitrogen-fixing bacterium associated with rice roots and rhizosphere soil. Res. Microbiol. 140, 679-693. 

Molina L, C Ramos, E Dnqne, MC Ronchel, JM Garcia, L Lyke, JL Ramos (2000) Snrvival of Pseudomonas putida KT2440 in soil and in the rhizosphere of plants nnder greenhonse and environmental conditions. Soil Biol Biochem 32 315-321. 

These results may be particularly relevant in the context of bioremediation, and lend support to the potential role of the rhizosphere and of plants (Chapters 12 and 14, Part 4). 

Mirleau P, R Wogelius, A Smith, MA Kertesz (2005) Importance of organosulfur utilization for survival of Pseudomonas putida in soil and rhizosphere. Appl Environ Microbiol 71 6571-6577. 

There has been considerable interest in the use of plants for bioremediation and this merits a rather extensive discussion. Plants can play an important role in bioremediation for several reasons (1) they can transport contaminants from the soil, (2) they can metabolize the contaminants after uptake, or (3) they can produce exudes that support microbial activity for degradation of the contaminants. In addition, bacteria can produce metabolites that counter the effect of toxins produced by fungi, and serve as biocontrol agents that diminish the need for the application of agrochemicals. Plant exudates play an important role in supporting the growth and activity of bacteria that carry out the degradation of contaminants in the rhizosphere and rhizoplane (the external surface of roots... 

Brazil GM, L Kenefick, M Callanan, A Haro, V de Lorenzo, DN Dowling, F O Gara (1995) Constrnction of a rhizosphere psendomonad with potential to degrade polychlorinated biphenyls and detection of bph gene expression in the rhizosphere. Appl Environ Microbiol 61 1946-1952. 

Leigh MB, JS Fletcher, X Fu, FJ Schmitz (2002) Root turnover an important source of microbial substrates in rhizosphere remediation of recalcitrant metabolites. Environ Sci Technol 36 1579-1583. 

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. 

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. 

Notz R, M Maurhofer, H Dubach, D Haas, G Defago (2002) Fusaric acid-producing strains of Fusarium oxysporum alter 2,4-diacetylphloroglucinol biosynthetic gene expression in Pseudomonas fluorescens CHAO and in the rhizosphere of wheat. Appl Environ Microbiol 68 2229-2235. 

Sarand I, S Timonen, E-L Nurmiaho-Lassila, T Koivula, K Haatela, M Romantschuk, R Sen (1998) Microbial biofilms and catabolic plasmid harbouring degradative fluorescent pseudomonads in Scots pine mycor-rhizospheres developed on petroleum contaminated soil. FEMS Microbiol Ecol 27 115-126. 

Siciliano SD, JJ Germida (1999) Enhanced phytoremediation of chlorobenzoates in rhizosphere soil. Soil Biol Biochem 31 299-305. 

The Rhizosphere as a Site of Biochemical Interactions Among Soil Components, Plants, and Microorganisms... 

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