scispace - formally typeset
Search or ask a question
Author

Christoph Keel

Bio: Christoph Keel is an academic researcher from University of Lausanne. The author has contributed to research in topics: Pseudomonas fluorescens & Pseudomonas protegens. The author has an hindex of 56, co-authored 107 publications receiving 10196 citations. Previous affiliations of Christoph Keel include École Polytechnique Fédérale de Lausanne & ETH Zurich.


Papers
More filters
Journal ArticleDOI
TL;DR: One challenge in future biocontrol research involves development of new strategies to overcome the broad toxicity and lack of antifungal specificity displayed by most biOControl antibiotics studied so far.
Abstract: Certain strains of fluorescent pseudomonads are important biological components of agricultural soils that are suppressive to diseases caused by pathogenic fungi on crop plants. The biocontrol abilities of such strains depend essentially on aggressive root colonization, induction of systemic resistance in the plant, and the production of diffusible or volatile antifungal antibiotics. Evidence that these compounds are produced in situ is based on their chemical extraction from the rhizosphere and on the expression of antibiotic biosynthetic genes in the producer strains colonizing plant roots. Well-characterized antibiotics with biocontrol properties include phenazines, 2,4-diacetylphloroglucinol, pyoluteorin, pyrrolnitrin, lipopeptides, and hydrogen cyanide. In vitro, optimal production of these compounds occurs at high cell densities and during conditions of restricted growth, involving (i) a number of transcriptional regulators, which are mostly pathway-specific, and (ii) the GacS/GacA two-component system, which globally exerts a positive effect on the production of extracellular metabolites at a posttranscriptional level. Small untranslated RNAs have important roles in the GacS/GacA signal transduction pathway. One challenge in future biocontrol research involves development of new strategies to overcome the broad toxicity and lack of antifungal specificity displayed by most biocontrol antibiotics studied so far.

788 citations

Journal ArticleDOI
TL;DR: It is concluded that bacterial cyanide is an important but not the only factor involved in suppression of black root rot in Pseudomonas fluorescens CHA0.
Abstract: Pseudomonas fluorescens CHA0 suppresses black root rot of tobacco, a disease caused by the fungus Thielaviopsis basicola. Strain CHA0 excretes several metabolites with antifungal properties. The importance of one such metabolite, hydrogen cyanide, was tested in a gnotobiotic system containing an artificial, iron-rich soil. A cyanidenegative (hcn) mutant, CHA5, constructed by a gene replacement technique, protected the tobacco plant less effectively than did the wild-type CHA0. Complementation of strain CHA5 by the cloned wild-type hcn+ genes restored the strain's ability to suppress disease. An artificial transposon carrying the hcn+ genes of strain CHA0 (Tnhcn) was constructed and inserted into the genome of another P.fluorescens strain, P3, which naturally does not produce cyanide and gives poor plant protection. The P3::Tnhcn derivative synthesized cyanide and exhibited an improved ability to suppress disease. All bacterial strains colonized the roots similarly and did not influence significantly the survival of T.basicola in soil. We conclude that bacterial cyanide is an important but not the only factor involved in suppression of black root rot.

660 citations

Journal ArticleDOI
TL;DR: Pseudomonas fluorescens strain CHAO suppresses Thielaviopsis basicola-induced black root rot of tobacco and Gaeumannomyces graminis var. tritici-induced take-all of wheat.
Abstract: Pseudomonas fluorescens strain CHAO suppresses Thielaviopsis basicola-induced black root rot of tobacco and Gaeumannomyces graminis var. tritici-induced take-all of wheat. Strain CHAO produces 2,4-diacetylphloroglucinol, a metabolite with antifungal, antibacterial, and phytotoxic activity. The role of this compound in disease suppression was tested under gnotobiotic conditions. A P. fluorescens mutant, obtained by Tn5 insertion, did not produce 2,4-diacetylphloroglucinol, showed diminished inhibition of T. basicola and of G. g. var. tritici in vitro, and had a reduced suppressive effect on tobacco black root rot and on take-all of wheat, compared with wild-type CHAO. Complementation of the mutant with an 11-kb DNA fragment from a genomic library of wild-type CHAO largely restored production of the metabolite, inhibition of the fungal pathogens in vitro and disease suppression. The Tn5 insertion was physically mapped using a 5.8-kb complementing fragment as a probe. 2,4- Diacetylphloroglucinol was shown to be produced in the rhizosphere of wheat by strain CHAO and by the complemented mutant, but not by the mutant defective in 2,4-diacetylphloroglucinol synthesis. These results support the importance of 2,4-diacetylphloroglucinol production by strain CHAO in the suppression of soilborne plant pathogens in the rhizosphere.

592 citations

Journal ArticleDOI
TL;DR: The shaping of the rhizomicrobiome is discussed and which aspects can be considered signaling are defined and divided into three categories: between microbes, from plants to microorganisms, and from microorganisms to plants.

400 citations

Journal ArticleDOI
TL;DR: The gacA mutants of strain CHA0 have a drastically reduced ability to suppress black root rot under gnotobiotic conditions, supporting the previous observations that the antibiotic Phl and HCN individually contribute to the suppression of blackroot rot.
Abstract: Pseudomonas fluorescens CHA0 colonizes plant roots, produces several secondary metabolites in stationary growth phase, and suppresses a number of plant diseases, including Thielaviopsis basicola-induced black root rot of tobacco. We discovered that mutations in a P. fluorescens gene named gacA (for global antibiotic and cyanide control) pleiotropically block the production of the secondary metabolites 2,4-diacetylphloroglucinol (Phl), HCN, and pyoluteorin. The gacA mutants of strain CHA0 have a drastically reduced ability to suppress black root rot under gnotobiotic conditions, supporting the previous observations that the antibiotic Phl and HCN individually contribute to the suppression of black root rot. The gacA gene is directly followed by a uvrC gene. Double gacA-uvrC mutations render P. fluorescens sensitive to UV irradiation. The gacA-uvrC cluster is homologous to the orf-2 (= uvrY)-uvrC operon of Escherichia coli. The gacA gene specifies a trans-active 24-kDa protein. Sequence data indicate that the GacA protein is a response regulator in the FixJ/DegU family of two-component regulatory systems. Expression of the gacA gene itself was increased in stationary phase. We propose that GacA, perhaps activated by conditions of restricted growth, functions as a global regulator of secondary metabolism in P. fluorescens.

390 citations


Cited by
More filters
01 Jan 2016
TL;DR: The modern applied statistics with s is universally compatible with any devices to read, and is available in the digital library an online access to it is set as public so you can download it instantly.
Abstract: Thank you very much for downloading modern applied statistics with s. As you may know, people have search hundreds times for their favorite readings like this modern applied statistics with s, but end up in harmful downloads. Rather than reading a good book with a cup of coffee in the afternoon, instead they cope with some harmful virus inside their laptop. modern applied statistics with s is available in our digital library an online access to it is set as public so you can download it instantly. Our digital library saves in multiple countries, allowing you to get the most less latency time to download any of our books like this one. Kindly say, the modern applied statistics with s is universally compatible with any devices to read.

5,249 citations

Journal ArticleDOI
TL;DR: This review restricts itself to bacteria that are derived from and exert this effect on the root and generally designated as PGPR (plant-growth-promoting rhizobacteria), which can be direct or indirect in their effects on plant growth.
Abstract: Several microbes promote plant growth, and many microbial products that stimulate plant growth have been marketed. In this review we restrict ourselves to bacteria that are derived from and exert this effect on the root. Such bacteria are generally designated as PGPR (plant-growth-promoting rhizobacteria). The beneficial effects of these rhizobacteria on plant growth can be direct or indirect. This review begins with describing the conditions under which bacteria live in the rhizosphere. To exert their beneficial effects, bacteria usually must colonize the root surface efficiently. Therefore, bacterial traits required for root colonization are subsequently described. Finally, several mechanisms by which microbes can act beneficially on plant growth are described. Examples of direct plant growth promotion that are discussed include (a) biofertilization, (b) stimulation of root growth, (c) rhizoremediation, and (d) plant stress control. Mechanisms of biological control by which rhizobacteria can promote plant growth indirectly, i.e., by reducing the level of disease, include antibiosis, induction of systemic resistance, and competition for nutrients and niches.

3,761 citations

Journal ArticleDOI
TL;DR: Overall, this review shows that soil microbes must be considered as important drivers of plant diversity and productivity in terrestrial ecosystems.
Abstract: Microbes are the unseen majority in soil and comprise a large portion of lifes genetic diversity. Despite their abundance, the impact of soil microbes on ecosystem processes is still poorly understood. Here we explore the various roles that soil microbes play in terrestrial ecosystems with special emphasis on their contribution to plant productivity and diversity. Soil microbes are important regulators of plant productivity, especially in nutrient poor ecosystems where plant symbionts are responsible for the acquisition of limiting nutrients. Mycorrhizal fungi and nitrogenfixing bacteria are responsible for c. 5‐20% (grassland and savannah) to 80% (temperate and boreal forests) of all nitrogen, and up to 75% of phosphorus, that is acquired by plants annually. Free-living microbes also strongly regulate plant productivity, through the mineralization of, and competition for, nutrients that sustain plant productivity. Soil microbes, including microbial pathogens, are also important regulators of plant community dynamics and plant diversity, determining plant abundance and, in some cases, facilitating invasion by exotic plants. Conservative estimates suggest that c. 20 000 plant species are completely dependent on microbial symbionts for growth and survival pointing to the importance of soil microbes as regulators of plant species richness on Earth. Overall, this review shows that soil microbes must be considered as important drivers of plant diversity and productivity in terrestrial ecosystems.

3,673 citations

Journal ArticleDOI
TL;DR: In this article, the authors discuss evidence that upon pathogen or insect attack, plants are able to recruit protective microorganisms, and enhance microbial activity to suppress pathogens in the rhizosphere.

3,228 citations

Journal ArticleDOI
TL;DR: The ways in which plant growth promoting rhizobacteria facilitate the growth of plants are considered and discussed and the possibility of improving plant growth promotion by specific genetic manipulation is critically examined.
Abstract: The ways in which plant growth promoting rhizobacteria facilitate the growth of plants are considered and discussed. Both indirect and direct mechanisms of plant growth promotion are dealt with. Th...

2,529 citations