Promise for plant pest control: root-associated pseudomonads with insecticidal activities.

Insects are an important and probably the most challenging pest to control in agriculture, in particular when they feed on belowground parts of plants. The application of synthetic pesticides is problematic owing to side effects on the environment, concerns for public health and the rapid development of resistance. Entomopathogenic bacteria, notably Bacillus thuringiensis and Photorhabdus/Xenorhabdus species, are promising alternatives to chemical insecticides, for they are able to efficiently kill insects and are considered to be environmentally sound and harmless to mammals. However, they have the handicap of showing limited environmental persistence or of depending on a nematode vector for insect infection. Intriguingly, certain strains of plant root-colonizing Pseudomonas bacteria display insect pathogenicity and thus could be formulated to extend the present range of bioinsecticides for protection of plants against root-feeding insects. These entomopathogenic pseudomonads belong to a group of plant-beneficial rhizobacteria that have the remarkable ability to suppress soil-borne plant pathogens, promote plant growth, and induce systemic plant defenses. Here we review for the first time the current knowledge about the occurrence and the molecular basis of insecticidal activity in pseudomonads with an emphasis on plant-beneficial and prominent pathogenic species. We discuss how this fascinating Pseudomonas trait may be exploited for novel root-based approaches to insect control in an integrated pest management framework

Evolutionary patchwork of an insecticidal toxin shared between plant-associated pseudomonads and the insect pathogens Photorhabdus and Xenorhabdus

Background: Root-colonizing fluorescent pseudomonads are known for their excellent abilities to protect plants against soil-borne fungal pathogens. Some of these bacteria produce an insecticidal toxin (Fit) suggesting that they may exploit insect hosts as a secondary niche. However, the ecological relevance of insect toxicity and the mechanisms driving the evolution of toxin production remain puzzling. Results: Screening a large collection of plant-associated pseudomonads for insecticidal activity and presence of the Fit toxin revealed that Fit is highly indicative of insecticidal activity and predicts that Pseudomonas protegens and P. chlororaphis are exclusive Fit producers. A comparative evolutionary analysis of Fit toxin-producing Pseudomonas including the insect-pathogenic bacteria Photorhabdus and Xenorhadus, which produce the Fit related Mcf toxin, showed that fit genes are part of a dynamic genomic region with substantial presence/absence polymorphism and local variation in GC base composition. The patchy distribution and phylogenetic incongruence of fit genes indicate that the Fit cluster evolved via horizontal transfer, followed by functional integration of vertically transmitted genes, generating a unique Pseudomonas-specific insect toxin cluster. Conclusions: Our findings suggest that multiple independent evolutionary events led to formation of at least three versions of the Mcf/Fit toxin highlighting the dynamic nature of insect toxin evolution

Potential environmental fate of elsinochrome A, a perylenequinone toxin produced in culture by bindweed biocontrol fungus Stagonospora convolvuli LA39

The photosensitizing perylenequinone toxin elsinochrome A (EA) is produced in culture by the bindweed biocontrol fungus Stagonospora convolvuli LA39 where it apparently plays a pathogenicity related role. We investigated the fate of EA with reference to its stability under different temperature and light conditions. EA remained stable when boiled in water at 100°C for 2 h. Similarly, exposing EA to 3-27°C in the dark for up to 16 weeks did not affect its stability either in dry or in aqueous form. However, results from irradiation experiments indicate that direct photolysis may be a significant degradation pathway for EA in the environment. EA either in dry form or dissolved in water was degraded by different irradiation wavelengths and intensities, with degradation plots fitting a first order rate kinetics. EA degraded faster if exposed in aqueous form, and at higher quantum flux density (μmol s−1 m−2). Sunlight was more effective in degrading EA than artificial white light and ultraviolet radiations (UV-A or UV-B). Exposing EA to natural sunlight, particularly, during the intense sunshine (1,420-1,640 μmol −1 m−2) days of 30 July to 5 August 2004 in Zurich caused the substance to degrade rapidly with half-life under such condition only 14 h. This implies that should EA gets into the environment, particularly on exposed environmental niches, such as on plant surfaces through biocontrol product spray, or released from shed diseased leaves, it may have no chance of accumulating to ‘level of concern'. Furthermore, a toxicity assay using Trichoderma atroviride P1 as biosensor showed that photo-degraded EA was not toxic, indicating that no stable toxic by-products were lef

Elsinochrome A production by the bindweed biocontrol fungus Stagonospora convolvuli LA39 does not pose a risk to the environment or the consumer of treated crops

Biological control as an alternative to chemical pesticides is of increasing public interest. However, to ensure safe use of biocontrol methods, strategies to assess the possible risks need to be developed. The production of toxic metabolites is an aspect which has so far largely been neglected in the risk assessment and the registration process for biocontrol products. We have evaluated the risks of elsinochrome A (ELA) and leptosphaerodione production by the fungus Stagonospora convolvuli LA39, an effective biocontrol agent used against bindweeds. The toxicity of the two metabolites to bacteria, protozoa, fungi and plants was evaluated in in vitro assays. The most sensitive bacteria and fungi were already affected at 0.01 0.07 μM ELA, whereas plants were far less sensitive. Leptosphaerodione was less toxic than ELA. Subsequently, it was investigated whether ELA is present in the applied biocontrol product or LA39-treated bindweed and crop plants. In plants ELA was never detected and in the biocontrol product the ELA concentration was far too low to have toxic effects even on the most sensitive organisms. We conclude that the production of ELA by biocontrol strain LA39 does not pose a risk to the environment or to the consume

Relationship between aggressiveness of Stagonospora sp. isolates on field and hedge bindweeds, and in vitro production of fungal metabolites cercosporin, elsinochrome A and leptosphaerodione

Stagonospora convolvuli LA39, an effective biocontrol agent of Convolvulus arvensis (field bindweed) and Calystegia sepium (hedge bindweed) produces phytotoxic metabolites leptosphaerodione and elsinochrome A. Stagonospora isolate 214Caa produces the toxin cercosporin. If toxic metabolite production is not linked to the pathogenic ability of the fungus on bindweeds, selection of aggressive strains with limited or no production of the metabolites would reduce any perceived risk of using strains of the fungus as a mycoherbicide. Therefore, 30 isolates of Stagonospora sp. including LA39 and 214Caa were characterised for aggressiveness on both bindweeds, and production of the three metabolites. Nine isolates were more aggressive than LA39 on both bindweeds. Classification of isolates based on metabolite type agreed largely with previous similar characterisation based on polymerase chain reaction-restriction fragment length polymorphism of internal transcribed spacer of ribosomal DNA. Cercosporin producers produced neither leptosphaerodione nor elsinochrome A and together with isolates that produce none of the three metabolites, were less pathogenic on bindweeds. Conversely, there was a positive correlation between elsinochrome A and leptosphaerodione production, and each was positively correlated with aggressiveness of isolates on both bindweeds. Generally, any isolate where elsinochrome A was not detected was not aggressive on any of the two bindweeds. This probably implies that selecting elsinochrome A-negative, but aggressive Stagonospora strain(s) may be difficult. However, aggressive isolates may not produce elsinochrome A in planta at levels that could constitute any risk in the environment. In a preliminary attempt to determine the levels of elsinochrome A and leptosphaerodione produced in diseased bindweeds, none of the toxins was detected in Stagonospora infected bindweed leaves. Detailed investigation focusing on the detection and quantification of in planta production of elsinochrome A by Stagonospora isolates, and determination of the fate of elsinochrome A in the environment, and its relationship with leptosphaerodione may be essential. Similarly, development of molecular tools to monitor the mycoherbicide following field application is vita

Signaling between bacterial and fungal biocontrol agents in a strain mixture

The use of bacterial and fungal strain mixtures is a promising way to improve efficacy of biocontrol treatments. Certain Pseudomonas and Trichoderma strains belong to the most common studied biocontrol agents. One key factor for the biocontrol efficacy of several P. fluorescens strains is the synthesis of 2,4-diacetylphloroglucinol (DAPG). Production of chitinases, such as the ECH42 endochitinase and the NAG1 N-acetyl-β-d-glucosaminidase, is a primary mechanism of action for T. atroviride. We examined the molecular interactions between the DAPG-producing P. fluorescens strains CHA0 and Q2-87 and chitinase-producing T. atroviride P1. Interactions were monitored using the reporter gene constructs, phlA'-'lacZ translational fusion in P. fluorescens CHA0 and ech42-goxA or nag1-goxA fusions in T. atroviride P1. We found that DAPG enhanced nag1, but not ech42 expression, whereas an unidentified substance from P. fluorescens CHA0 repressed expression of both Trichoderma chitinases. Addition of T. atroviride P1 culture filtrates to growing cultures of P. fluorescens enhanced phlA expression transiently during growth. These results indicate that negative and positive effects on expression of key biocontrol genes may occur while mixing antagonist

Full-genome sequence of the plant growth-promoting bacterium Pseudomonas protegens CHA0.

We report the complete genome sequence of the free-living bacterium Pseudomonas protegens (formerly Pseudomonas fluorescens) CHA0, a model organism used in plant-microbe interactions, biological control of phytopathogens, and bacterial genetics

Evolutionary patchwork of an insecticidal toxin shared between plant-associated pseudomonads and the insect pathogens Photorhabdus and Xenorhabdus.

BACKGROUND: Root-colonizing fluorescent pseudomonads are known for their excellent abilities to protect plants against soil-borne fungal pathogens. Some of these bacteria produce an insecticidal toxin (Fit) suggesting that they may exploit insect hosts as a secondary niche. However, the ecological relevance of insect toxicity and the mechanisms driving the evolution of toxin production remain puzzling. RESULTS: Screening a large collection of plant-associated pseudomonads for insecticidal activity and presence of the Fit toxin revealed that Fit is highly indicative of insecticidal activity and predicts that Pseudomonas protegens and P. chlororaphis are exclusive Fit producers. A comparative evolutionary analysis of Fit toxin-producing Pseudomonas including the insect-pathogenic bacteria Photorhabdus and Xenorhadus, which produce the Fit related Mcf toxin, showed that fit genes are part of a dynamic genomic region with substantial presence/absence polymorphism and local variation in GC base composition. The patchy distribution and phylogenetic incongruence of fit genes indicate that the Fit cluster evolved via horizontal transfer, followed by functional integration of vertically transmitted genes, generating a unique Pseudomonas-specific insect toxin cluster. CONCLUSIONS: Our findings suggest that multiple independent evolutionary events led to formation of at least three versions of the Mcf/Fit toxin highlighting the dynamic nature of insect toxin evolution

Biologische Schädlingskontrolle adulter Japankäfer mit entomopathogenen Pilzen

"Der Japankäfer (Popillia japonica) ist ein invasiver Schädling, der mit seiner polyphagen Lebensweise die europäische Landwirtschaft bedroht. Mit dem Einsatz von ""attract-and-infest"" Fallen werden erwachsene Käfer als Vektoren benutzt, um einen entomopathogenen Pilz in der Population zu verbreiten.

Biological Control of pathogenic fungi: problems in the transfer from research to application

Im vorliegenden Beitrag werden einige erfolgreiche und nicht erfolgreiche Beispiele für die Bekämpfung pflanzenpathogener Pilze mit lebenden Organismen analysiert, und die Unterschiede zur meist erfolgreicheren biologischen Bekämpfung von Arthropoden werden aufgezeigt.In this presentation some examples of successful and unsuccessful control of phytopathogenic fungi through biological living agents are analyzed and the differences with the more successful biocontrol of arthropodes are mentioned