The Caenorhabditis elegans assay: A tool to evaluate the pathogenic potential of bacterial biocontrol agents

European Journal of Plant Pathology (Impact Factor: 1.49). 11/2009; 125(3):367-376. DOI: 10.1007/s10658-009-9486-3


Bacterial biocontrol agents (BCAs) open up the possibility of controlling plant pathogens in an environmentally friendly way.
Although they are naturally occurring microbes, some of them can cause diseases in humans. For successful registration it
is necessary to test potentially adverse effects on the human health of at-risk candidates. Existing pathogenicity assays
are cost-intensive, time-consuming and furthermore they are often inappropriate for facultative pathogens. We developed a
new, fast and inexpensive bioassay on the basis of the nematode Caenorhabditis elegans, which is a well-accepted model organism to study bacterial pathogenicity. A selection of eight strains from clinical and
environmental origin as well as potential and commercial BCAs from the genera Bacillus, Pseudomonas, Serratia and Stenotrophomonas were screened for their potential to kill the nematode in an in vitro agar plate assay. Furthermore, the motility and reproductive behaviour of nematodes exposed to strains were tested in comparison
with those fed by the human pathogen Pseudomonas aeruginosa QC14-3-8 (positive control) and the negative control Escherichia coli OP50. Commercial as well as potential biocontrol strains did not display any adverse effects in all tests. In contrast, the
C. elegans assay showed slight effects for clinical and environmental Stenotrophomonas strains. Results showed that the nematode C. elegans provides a model system to indicate the pathogenic potential of BCAs in a very early stage of product development.

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    • "Symbiotic Burkholderia species are not pathogenic to the nematode C. elegans: Exposing the model organism C. elegans to bacterial strains is frequently used to assess the severity of bacterial pathogenesis [47], [48]. Using the “slow killing” assay, we compared the effects of the standard nematode food source, E. coli OP50 to B. thailandensis E264, as well as to a number of Burkholderia species from the A group (Fig. 6). "
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    ABSTRACT: Burkholderia is a diverse and dynamic genus, containing pathogenic species as well as species that form complex interactions with plants. Pathogenic strains, such as B. pseudomallei and B. mallei, can cause serious disease in mammals, while other Burkholderia strains are opportunistic pathogens, infecting humans or animals with a compromised immune system. Although some of the opportunistic Burkholderia pathogens are known to promote plant growth and even fix nitrogen, the risk of infection to infants, the elderly, and people who are immunocompromised has not only resulted in a restriction on their use, but has also limited the application of non-pathogenic, symbiotic species, several of which nodulate legume roots or have positive effects on plant growth. However, recent phylogenetic analyses have demonstrated that Burkholderia species separate into distinct lineages, suggesting the possibility for safe use of certain symbiotic species in agricultural contexts. A number of environmental strains that promote plant growth or degrade xenobiotics are also included in the symbiotic lineage. Many of these species have the potential to enhance agriculture in areas where fertilizers are not readily available and may serve in the future as inocula for crops growing in soils impacted by climate change. Here we address the pathogenic potential of several of the symbiotic Burkholderia strains using bioinformatics and functional tests. A series of infection experiments using Caenorhabditis elegans and HeLa cells, as well as genomic characterization of pathogenic loci, show that the risk of opportunistic infection by symbiotic strains such as B. tuberum is extremely low.
    PLoS ONE 01/2014; 9(1):e83779. DOI:10.1371/journal.pone.0083779 · 3.23 Impact Factor
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    • "The use of C. elegans is becoming increasingly popular in invertebrate animal testing of substances used in pharmaceutical or cosmetic applications (Leung et al. 2008). It is a widely accepted model organisms to test bacteria pathogenicity and has hence been proposed to test the newly emerging group of bacterial plant protection agents (Zachow et al. 2012). As well as testing undesirable side effects, C. elegans can be used to test desirable effects of pharmaceutic substances , since it can easily be genetically transformed to display typical elements of human diseases. "
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    ABSTRACT: While nematodes are most commonly known for their negative impact on plants, animals, and humans, there are a number of species which are commercially explored. This review highlights some of the most important success stories for the application of nematodes. They are used as bioindicators in ecological and toxicity studies, as model organisms for elucidating fundamental biological questions and for high throughput screening of drugs. Besides these indirect uses, direct applications include the use of Beddingia siricidicola against a major forest pest and the commercialization of Steinernema, Heterorhabditis, and Phasmarhabditis as biological pest control products. New directions for the commercialization of nematodes are the use as living food, specifically loaded with essential nutrients for various fish and shrimp larvae. Even human parasites or closely related species have been successfully used for curing autoimmune disorders and are currently in the process of being developed as drugs. With the striving development of life sciences, we are likely to see more applications for nematodes in the future. A prerequisite is that we continue to explore the vast number of yet undiscovered nematode species.
    Applied Microbiology and Biotechnology 06/2013; 97(14). DOI:10.1007/s00253-013-4941-7 · 3.34 Impact Factor
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    • "In addition, strains able to grow at 37 • C, the temperature of the human body, should be rejected from further development as well (Fravel et al., 1999). Finally, the use of a bioassay with the nematode Caenorhabditis elegans can be a helpful tool for the evaluation of pathogenicity of the candidate strains (Zachow et al., 2009). It should be noted that the three methods described above provide a good impression of the safety of strains used in the development of a product. "
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    ABSTRACT: The development of microbial inoculants for specific crops is a multistage process with participation of scientific researchers and industry. The process starts with isolation/selection of potential strains with desired properties such as plant growth stimulation, enhancement of availability of vitally important nutrients and therefore improvement of plant nutrition, amelioration of biotic and abiotic stress, degradation of pollutants, and biological control of phytopathogenic microbes. Subsequent assessment of the potentially promising strains for safety, the development of industrial production protocols and suitable formulations, registration and marketing are the most costly and time consuming steps in product development. Elucidation of dominant properties of the strain will help to choose correct strategy for positioning of the product on the market of microbial inoculants. The evaluation of examples of selected products based on Trichoderma harzianum T22, Bacillus subtilis FZB24, Bacillus amyloliquefaciens FZB42 and Pseudomonas chlororaphis MA342 provides important insights of successful transfer of academically gained knowledge in commercially successful microbial products used worldwide. Major challenges in development, registration and marketing of microbial inoculants are discussed.
    Molecular Microbial Ecology of the Rhizosphere, Volume 2, First edited by Frans J. de Brujn, 03/2013: chapter Plant Growth Promoting Microorganisms: The Road from an Academically Promising Results to a Commercial Product; John Wiley & Sons, Inc..
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