Do soil protozoa enhance plant growth by hormonal effects?

Bonkowski, Michael; Brandt, Fritz

doi:10.1016/s0038-0717(02)00157-8

Cited by 158 publications

(93 citation statements)

References 34 publications

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“…Positive effects of bacteria-protozoa interactions on plant growth are well documented (Bonkowski 2004) and recent findings strongly indicated that grazing induced shifts in bacterial diversity and function are responsible for plant growth promoting effects of bacterial grazers (Bonkowski and Brandt, 2002;Kreuzer et al, 2006;Mao et al, 2007). In fact, shoot and root biomass of A. thaliana increased significantly in presence of amoebae and the early growth response of plants was not linked to increased nutrient availability from consumed bacterial biomass (Krome et al, 2009).…”

Section: Discussionmentioning

confidence: 99%

“…Soil protozoa are known to promote plant growth (Bonkowski, 2004) and recent investigations indicate that plant growth promotion by microfaunal predators, such as protozoa and nematodes, may be based on grazing induced changes in rhizosphere bacterial community composition and subsequent favouring of plant growth-promoting bacteria (Bonkowski and Brandt, 2002;Kreuzer et al, 2006;Mao et al, 2006). Among Gram-negative bacteria, pseudomonads are a particular important group of plant growth-promoting rhizobacteria.…”

Section: Introductionmentioning

confidence: 99%

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Soil amoebae rapidly change bacterial community composition in the rhizosphere of Arabidopsis thaliana

Rosenberg¹,

Bertaux²,

Krome³

et al. 2009

The ISME Journal

219

183

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We constructed an experimental model system to study the effects of grazing by a common soil amoeba, Acanthamoeba castellanii, on the composition of bacterial communities in the rhizosphere of Arabidopsis thaliana. Amoebae showed distinct grazing preferences for specific bacterial taxa, which were rapidly replaced by grazing tolerant taxa in a highly reproducible way. The relative proportion of active bacteria increased although bacterial abundance was strongly decreased by amoebae. Specific bacterial taxa had disappeared already two days after inoculation of amoebae. The decrease in numbers was most pronounced in Betaproteobacteria and Firmicutes. In contrast, Actinobacteria, Nitrospira, Verrucomicrobia and Planctomycetes increased. Although other groups, such as betaproteobacterial ammonia oxidizers and Gammaproteobacteria did not change in abundance, denaturing gradient gel electrophoresis with specific primers for pseudomonads (Gammaproteobacteria) revealed both specific changes in community composition as well as shifts in functional genes (gacA) involved in bacterial defence responses. The resulting positive feedback on plant growth in the amoeba treatment confirms that bacterial grazers play a dominant role in structuring bacteria-plant interactions. This is the first detailed study documenting how rapidly protozoan grazers induce shifts in rhizosphere bacterial community composition.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Soil amoebae rapidly change bacterial community composition in the rhizosphere of Arabidopsis thaliana

Rosenberg¹,

Bertaux²,

Krome³

et al. 2009

The ISME Journal

219

183

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“…Amoeba can change the rice root architecture and community composition of bacteria (Bonkowski 2004). Although it is still questionable, it is suggested that amoeba functions as bacteria-mediated mutualists promoting plant growth by hormonal feedback mechanisms and nutrient effects based on nutrient release from grazed bacterial biomass (Bonkowski and Brandt 2002). On the other hand, amoeba distantly related to Saccamoeba in BlastN search were detected only in the wheat rhizosphere (Table 1, Supporting Information, Fig.…”

Section: Phylogeny Of Microeukaryotes In the Rice Rhizospherementioning

confidence: 99%

Community structure of microeukaryotes in a rice rhizosphere revealed by DNA-based PCR-DGGE

Asiloglu

Honjo²,

Saka³

et al. 2015

Soil Science and Plant Nutrition

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Rice roots provide a specific habitat for microorganisms in the rhizosphere of a submerged field through supply of oxygen and organic matter. Many studies have focused on the microbial community in the rice rhizosphere, but less is still known about the microeukaryotic community structure of rice rhizosphere. This study explored the microeukaryotic community structure of a rice rhizosphere through denaturing gradient gel electrophoresis (DGGE) targeting 18S rRNA gene. The rice roots and the rhizosphere soil samples, which were collected from a field under rice-wheat rotation system, were separately analyzed. To characterize the rice rhizosphere-specific community, the bulk soil of rice field and the wheat rhizosphere samples were also examined. DGGE fingerprints showed that the microeukaryotic community of rice roots were distinct from the community of the bulk soil and showed a temporal shift with the growth stage. The rhizosphere soil community was distinct from the root and bulk soil communities, but this could be explained by that the root and bulk soil communities were shared in the rhizosphere. The rice rhizosphere community was also distinct from those in the wheat rhizosphere. Microeukaryotes that characterized the rice rhizosphere (roots and the rhizosphere soil) community could be affiliated to Polymyxa, flagellates, and oomycetes, which suggested that microeukaryotes with various ecological roles, e.g., parasites, bacterial grazers, and decomposers, inhabit the rice rhizosphere. The results showed that the rice root and its growth stages are key factors shaping the microeukaryotic community structure in the rhizosphere.

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“…The naked amoebae (Acanthamoeba castellanii) isolated from a woodland soil (Bonkowski and Brandt, 2002) were grown axenically on peptoneyeast extract-glucose (PYG) medium (peptone 20 g l À1 , yeast extract 5 g l À1 , glucose 10gl…”

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confidence: 99%

Predators promote defence of rhizosphere bacterial populations by selective feeding on non-toxic cheaters

et al. 2009

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Soil pseudomonads increase their competitiveness by producing toxic secondary metabolites, which inhibit competitors and repel predators. Toxin production is regulated by cell-cell signalling and efficiently protects the bacterial population. However, cell communication is unstable, and natural populations often contain signal blind mutants displaying an altered phenotype defective in exoproduct synthesis. Such mutants are weak competitors, and we hypothesized that their fitness depends on natural communities on the exoproducts of wild-type bacteria, especially defence toxins. We established mixed populations of wild-type and signal blind, non-toxic gacS-deficient mutants of Pseudomonas fluorescens CHA0 in batch and rhizosphere systems. Bacteria were grazed by representatives of the most important bacterial predators in soil, nematodes (Caenorhabditis elegans) and protozoa (Acanthamoeba castellanii). The gacS mutants showed a negative frequency-dependent fitness and could reach up to one-third of the population, suggesting that they rely on the exoproducts of the wild-type bacteria. Both predators preferentially consumed the mutant strain, but populations with a low mutant load were resistant to predation, allowing the mutant to remain competitive at low relative density. The results suggest that signal blind Pseudomonas increase their fitness by exploiting the toxins produced by wild-type bacteria, and that predation promotes the production of bacterial defence compounds by selectively eliminating non-toxic mutants. Therefore, predators not only regulate population dynamics of soil bacteria but also structure the genetic and phenotypic constitution of bacterial communities.

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Do soil protozoa enhance plant growth by hormonal effects?

Cited by 158 publications

References 34 publications

Soil amoebae rapidly change bacterial community composition in the rhizosphere of Arabidopsis thaliana

Soil amoebae rapidly change bacterial community composition in the rhizosphere of Arabidopsis thaliana

Community structure of microeukaryotes in a rice rhizosphere revealed by DNA-based PCR-DGGE

Predators promote defence of rhizosphere bacterial populations by selective feeding on non-toxic cheaters

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