Protozoan response to addition of the bacteria Mycobacterium chlorophenolicum and Pseudomonas chlororaphis to soil microcosms

Rønn, Regin; Grunert, J.

doi:10.1007/s003740000299

Cited by 37 publications

(18 citation statements)

References 27 publications

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“…Establishment and persistence of microorganisms harbouring pdo1 genes in the street dust amended microcosms indicate that these genes are important players in the degradation of environmental PAHs. The persistence of pdo1-genes, presumably originating from mycobacteria and related organisms, is in good accordance with a previous study, which showed that indigenous protozoa in soil microcosms did not graze on mycobacterial cells, whereas Pseudomonas cells, the classical host of nah-genes, were rapidly eliminated (Rønn et al, 2001).…”

Section: Discussionsupporting

confidence: 92%

Microbial degradation of street dust polycyclic aromatic hydrocarbons in microcosms simulating diffuse pollution of urban soil

Johnsen

Lipthay

Sørensen

et al. 2006

Environmental Microbiology

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Diffuse pollution with polycyclic aromatic hydrocarbons (PAHs) of topsoil in urban regions has caused increasing concerns in recent years. We simulated diffuse pollution of soil in microcosms by spiking sandy topsoil (A-horizon) and coarse, mineral subsoil (C-horizon) with street dust (PM63) isolated from municipal street sweepings from central Copenhagen. The microbial communities adapted to PAH degradation in microcosms spiked with street dust in both A-horizon and C-horizon soils, in spite of low PAH-concentrations. The increased potential for PAH degradation was demonstrated on several levels: by slowly diminishing PAH-concentrations, increased mineralization of 14C-PAHs, increasing numbers of PAH degraders and increased prevalence of nah and pdo1 PAH degradation genes, i.e. the microbial communities quickly adapted to PAH degradation. Three- and 4-ring PAHs from the street dust were biodegraded to some extent (10-20%), but 5- and 6-ring PAHs were not biodegraded in spite of frequent soil mixing and high PAH degradation potentials. In addition to biodegradation, leaching of 2-, 3- and 4-ring PAHs from the A-horizon to the C-horizon seems to reduce PAH-levels in surface soil. Over time, levels of 2-, 3- and 4-ring PAHs in surface soil may reach equilibrium between input and the combination of biodegradation and leaching. However, levels of the environmentally critical 5- and 6-ring PAHs will probably continue to rise. We presume that sorption to black carbon particles is responsible for the persistence and low bioaccessibility of 5- and 6-ring PAHs in diffusely polluted soil.

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Section: Discussionsupporting

confidence: 92%

Microbial degradation of street dust polycyclic aromatic hydrocarbons in microcosms simulating diffuse pollution of urban soil

Johnsen

Lipthay

Sørensen

et al. 2006

Environmental Microbiology

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“…Hence, the total aphid-induced respiration increase amounts to 1,411 μg CO 2 -C pot −1 . If we assume that protozoan half-life is not <8 days (Rønn et al 2001;de Ruiter et al 1993) the aphid-induced protozoan increase would give rise to a maximum of 2,800 μg CO 2 -C pot −1 during the 16 days of herbivory. The measured cumulated effects of aphids on belowground respiration during the 16 days of aphid presence before spike emergence in NP amounts to 144 μg CO 2 -C g −1 soil corresponding to 144 mg CO 2 -C for the pots with 1,000 g soil.…”

Section: Discussionmentioning

confidence: 99%

Aphid effects on rhizosphere microorganisms and microfauna depend more on barley growth phase than on soil fertilization

2004

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This paper gives the first reports on aphid effects on rhizosphere organisms as influenced by soil nutrient status and plant development. Barley plants grown in pots fertilized with N but without P (N), with N and P (NP), or not fertilized (0) were sampled in the early growth phase (day 25), 1 week before and 1 week after spike emergence. Aphids were added 16 days before sampling was carried out. In a separate experiment belowground respiration was measured on N and NP fertilized plant-soil systems with aphid treatments comparable to the first experiment. Aphids reduced numbers of rhizosphere bacteria and fungal feeding nematodes 1 week before spike emergence. Before spike emergence, aphids reduced belowground respiration in NP treatments. These findings strongly indicate that aphids reduced allocation of photoassimilates to roots and deposition of root exudates in the growth phase of the plant. Contrary to this, 1 week after spike emergence numbers of bacteria, fungal feeding nematodes and Protozoa were higher in rhizospheres of plants subjected to aphids probably because aphids enhanced root mortality and root decomposition. Protozoa and bacterial feeding nematodes were stimulated at different experimental conditions with nematodes being the dominant bacterial grazers at N fertilization and Protozoa in the NP treatment before spike emergence.

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“…P. fluorescens CHA0 isogenic mutants that do not produce exometabolites have reduced colonization ability when they are inoculated into a natural soil (20), but no difference from wild-type CHA0 was observed in sterile microcosms (43). In this study we analyzed one of the possible interactions between P. fluorescens and other soil organisms, i.e., the susceptibility to predation by protists, as protists have been found to determine the survival of inoculated bacteria (32,39). Under our experimental conditions, the production of extracellular compounds appears to help bacteria avoid predation (Table 3).…”

Section: Discussionmentioning

confidence: 99%

Secondary Metabolites Help Biocontrol Strain Pseudomonas fluorescens CHA0 To Escape Protozoan Grazing

Jousset

Lara

Wall

et al. 2006

Appl Environ Microbiol

179

190

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In soil ecosystems, bacteria must cope with predation activity, which is attributed mainly to protists. The development of antipredation strategies may help bacteria maintain higher populations and persist longer in the soil. We analyzed the interaction between the root-colonizing and biocontrol strain Pseudomonas fluorescens CHA0 and three different protist isolates (an amoeba, a flagellate, and a ciliate). CHA0 produces a set of antibiotics, HCN, and an exoprotease. We observed that protists cannot grow on CHA0 but can multiply on isogenic regulatory mutants that do not produce the extracellular metabolites. The in vitro responses to CHA0 cells and its exoproducts included growth inhibition, encystation, paralysis, and cell lysis. By analyzing the responses of protists to bacterial supernatants obtained from different isogenic mutants whose production of one or more exometabolites was affected and also to culture extracts with antibiotic enrichment, we observed different contributions of the phenolic antifungal compound 2,4-diacetylphloroglucinol (DAPG) and the extracellular protease AprA to CHA0 toxicity for protists and to the encystation-reactivation cycle. The grazing pressure artificially produced by a mixture of the three protists in a microcosm system resulted in reduced colonization of cucumber roots by a regulatory isogenic CHA0 mutant unable to produce toxins. These results suggest that exometabolite production in biocontrol strain CHA0 may contribute to avoidance of protist grazing and help sustain higher populations in the rhizosphere, which may be a desirable and advantageous trait for competition with other bacteria for available resources.

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Protozoan response to addition of the bacteria Mycobacterium chlorophenolicum and Pseudomonas chlororaphis to soil microcosms

Cited by 37 publications

References 27 publications

Microbial degradation of street dust polycyclic aromatic hydrocarbons in microcosms simulating diffuse pollution of urban soil

Microbial degradation of street dust polycyclic aromatic hydrocarbons in microcosms simulating diffuse pollution of urban soil

Aphid effects on rhizosphere microorganisms and microfauna depend more on barley growth phase than on soil fertilization

Secondary Metabolites Help Biocontrol Strain Pseudomonas fluorescens CHA0 To Escape Protozoan Grazing

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