Rhizosphere Ecology of Xenobiotic-Degrading Microorganisms

Crowley, David E.; Alvey, S.; Gilbert, Eric S

doi:10.1021/bk-1997-0664.ch002

Cited by 41 publications

(30 citation statements)

References 24 publications

(33 reference statements)

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“…One suggested reason for rhizosphere-enhanced biodegradation is the possible presence, as a result of rhizodeposition, of high densities of active and diverse heterotrophic microorganisms on root surfaces, a situation which will facilitate complex degradative pathways through activities of consortia and conjugative horizontal transfer of catabolic genes carried on mobile genetic elements (6). Another suggested reason for rhizosphere-enhanced xenobiotic biodegradation is that components of the rhizodeposits (exudates, root materials, or their decomposition products) may be structural analogs for the pollutant in question (6,20).…”

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confidence: 99%

“…Another suggested reason for rhizosphere-enhanced xenobiotic biodegradation is that components of the rhizodeposits (exudates, root materials, or their decomposition products) may be structural analogs for the pollutant in question (6,20). It follows that the presence of a pollutant analog in the rhizosphere may select for pollutantdegrading microorganisms capable of directly using the analog for growth, act as a cooxidized substrate during cometabolism, or serve as an effector molecule in the induction of xenobiotic catabolic pathways (43).…”

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confidence: 99%

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Enhanced Mineralization of [U- ¹⁴ C]2,4-Dichlorophenoxyacetic Acid in Soil from the Rhizosphere of Trifolium pratense

Shaw

Burns

2004

Appl Environ Microbiol

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Enhanced biodegradation in the rhizosphere has been reported for many organic xenobiotic compounds, although the mechanisms are not fully understood. The purpose of this study was to discover whether rhizosphere-enhanced biodegradation is due to selective enrichment of degraders through growth on compounds produced by rhizodeposition. We monitored the mineralization of [U-14 C]2,4-dichlorophenoxyacetic acid (2,4-D) in rhizosphere soil with no history of herbicide application collected over a period of 0 to 116 days after sowing of Lolium perenne and Trifolium pratense. The relationships between the mineralization kinetics, the number of 2,4-D degraders, and the diversity of genes encoding 2,4-D/␣-ketoglutarate dioxygenase (tfdA) were investigated. The rhizosphere effect on [ 14 C]2,4-D mineralization (50 g g ؊1 ) was shown to be plant species and plant age specific. In comparison with nonplanted soil, there were significant (P < 0.05) reductions in the lag phase and enhancements of the maximum mineralization rate for 25-and 60-day T. pratense soil but not for 116-day T. pratense rhizosphere soil or for L. perenne rhizosphere soil of any age. Numbers of 2,4-D degraders in planted and nonplanted soil were low (most probable number, <100 g ؊1 ) and were not related to plant species or age. Single-strand conformational polymorphism analysis showed that plant species had no impact on the diversity of ␣-Proteobacteria tfdA-like genes, although an impact of 2,4-D application was recorded. Our results indicate that enhanced mineralization in T. pratense rhizosphere soil is not due to enrichment of 2,4-D-degrading microorganisms by rhizodeposits. We suggest an alternative mechanism in which one or more components of the rhizodeposits induce the 2,4-D pathway.The rhizosphere is the zone of soil directly influenced by the presence of plant roots. It receives inputs of an array of low (e.g., sugars, organic and amino acids, phenolics, and other secondary metabolites)-and high (e.g., cellulose, lignin, mucilage, proteins)-molecular-mass compounds as a result of rhizodeposition and is a zone of complex plant-microbe interactions (56). Seminal work by Hsu and Bartha (23) demonstrated that mineralization of organophosphate pesticides in the rhizosphere is increased relative to that in nonplanted soils. Since this study, numerous reports of rhizosphere-enhanced biodegradation have been published for several classes of organic pollutants, including polyaromatic (2, 35, 48) and aliphatic (5, 38, 48) hydrocarbons, chlorophenols (3, 13

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confidence: 99%

Enhanced Mineralization of [U- ¹⁴ C]2,4-Dichlorophenoxyacetic Acid in Soil from the Rhizosphere of Trifolium pratense

Shaw

Burns

2004

Appl Environ Microbiol

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“…The current emphasis is on the development of microbial inoculants for biological control of pests (21,42,53), for promoting plant growth (32,38), and more recently, for plant-assisted microbial elimination of pollutants (7,18). In all of these cases and independent of the specific ecological conditions required by different agricultural practices, successful use of microbial inoculants in the field requires efficient colonization of the root system and a high level of competence of the introduced microbe for the desired biological property (e.g., production of antibiotics or plant growth-stimulating hormones or biosynthesis of catabolic enzymes for degradation of xenobiotic compounds) to be expressed.…”

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confidence: 99%

Bacterial Activity in the Rhizosphere Analyzed at the Single-Cell Level by Monitoring Ribosome Contents and Synthesis Rates

Ramos

Mølbak

Molin

2000

Appl Environ Microbiol

165

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The growth activity of Pseudomonas putida cells colonizing the rhizosphere of barley seedlings was estimated at the single-cell level by monitoring ribosomal contents and synthesis rates. Ribosomal synthesis was monitored by using a system comprising a fusion of the ribosomal Escherichia coli rrnBP1 promoter to a gene encoding an unstable variant of the green fluorescent protein (Gfp). Gfp expression in a P. putida strain carrying this system inserted into the chromosome was strongly dependent on the growth phase and growth rate of the strain, and cells growing exponentially at rates of >0.17 h ؊1 emitted growth rate-dependent green fluorescence detectable at the single-cell level. The single-cell ribosomal contents were very heterogeneous, as determined by quantitative hybridization with fluorescently labeled rRNA probes in P. putida cells extracted from the rhizosphere of 1-day-old barley seedlings grown under sterile conditions. After this, cells extracted from the root system had ribosomal contents similar to those found in starved cells. There was a significant decrease in the ribosomal content of P. putida cells when bacteria were introduced into nonsterile bulk or rhizosphere soil, and the Gfp monitoring system was not induced in cells extracted from either of the two soil systems. The monitoring system used permitted nondestructive in situ detection of fast-growing bacterial microcolonies on the sloughing root sheath cells of 1-and 2-day-old barley seedlings grown under sterile conditions, which demonstrated that it may be possible to use the unstable Gfp marker for studies of transient gene expression in plant-microbe systems.

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“…Lo observado en la Figura 2 anterior no corrobora lo expuesto por Burgues y Raw (1971), Anderson et al (1994) entre otros, al airmar que la actividad microbiana aumenta en la rizósfera. Sin embargo es resaltante el hecho de que el tratamiento T4 (suelo con atrazina, sin sustrato y no esterilizado) fue el único cuyo numero de U.F.C./g de suelo en la muestra tomada cerca de la rizósfera fue superior a la muestra de suelo tomada a 8 cm del tallo, ratiicando lo sustentado por Crowley et al (1997) y otros, quienes airman que la degradación de atrazina es mayor en la rizósfera y el núme-ro de organismos en ella es superior que en el suelo circundante.…”

Section: Bacteriasunclassified

“…Lo observado en la Figura 4 se aprecia muy claramente que la actividad microbiana aumentó en el suelo cercano a la rizósfera concordando por lo expuesto por Anderson et al (1994), Burges y Raw (1971), entre otros. Además al observar el tratamiento T4 ( suelo con atrazina, sin sustrato y no esterilizado) se ratiica lo sustentado por Crowley et al (1997) entre otros, quienes dicen que la degradación de atrazina es mayor en la rizósfera y el núme-ro de organismos es superior que en el suelo circundante.…”

Section: Grupos Específicos Bacterias Amoniicantes Lo Observado En Launclassified

Efecto del Herbicida Atrazina sobre la Población de Bacterias en un Suelo del Municipio de Saldaña, Tolima

Lagos

Fuentes

2006

Colomb. For.

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Rhizosphere Ecology of Xenobiotic-Degrading Microorganisms

Cited by 41 publications

References 24 publications

Enhanced Mineralization of [U- ¹⁴ C]2,4-Dichlorophenoxyacetic Acid in Soil from the Rhizosphere of Trifolium pratense

Enhanced Mineralization of [U- ¹⁴ C]2,4-Dichlorophenoxyacetic Acid in Soil from the Rhizosphere of Trifolium pratense

Bacterial Activity in the Rhizosphere Analyzed at the Single-Cell Level by Monitoring Ribosome Contents and Synthesis Rates

Efecto del Herbicida Atrazina sobre la Población de Bacterias en un Suelo del Municipio de Saldaña, Tolima

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Rhizosphere Ecology of Xenobiotic-Degrading Microorganisms

Cited by 41 publications

References 24 publications

Enhanced Mineralization of [U- 14 C]2,4-Dichlorophenoxyacetic Acid in Soil from the Rhizosphere of Trifolium pratense

Enhanced Mineralization of [U- 14 C]2,4-Dichlorophenoxyacetic Acid in Soil from the Rhizosphere of Trifolium pratense

Bacterial Activity in the Rhizosphere Analyzed at the Single-Cell Level by Monitoring Ribosome Contents and Synthesis Rates

Efecto del Herbicida Atrazina sobre la Población de Bacterias en un Suelo del Municipio de Saldaña, Tolima

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Enhanced Mineralization of [U- ¹⁴ C]2,4-Dichlorophenoxyacetic Acid in Soil from the Rhizosphere of Trifolium pratense

Enhanced Mineralization of [U- ¹⁴ C]2,4-Dichlorophenoxyacetic Acid in Soil from the Rhizosphere of Trifolium pratense