Plant-associated pseudomonads as a potential reservoir for novel insecticidal toxins

• Research unit: COST
• Project number: C07.0026

Key words (English)

Pseudomonas; plant-beneficial; toxin; insecticidal; agricultural pest; biological control; rhizosphere; molecular plant-microbe interactions

Research programs (English)

COST-Action 862 - Bacterial toxins for insect control

Short description (English)

The project is based on our exciting discovery that certain root-colonizing pseudomonads that protect crop plants from fungal diseases also have potent insecticidal activity. The focus is on the molecular characterization of the genomic region encoding the anti-insect action and the regulatory elements involved. The spectrum of activity of the novel insecticidal toxin and the occurrence and diversity of the toxin genes in plant-associated pseudomonads will be monitored.

Further information (English)

Full name of research-institution/enterprise: Université de Lausanne Institut de Microbiologie Fondamentale

Partners and International Organizations (English)

BE, BG, CH, CY, CZ, DE, DK, ES, FR, GR, IL, IT, LV, MK, NL, PL; SK, TR, UK

Abstract (English)

Fungal diseases and insect pests cause major damage to agricultural crops and they are very difficult to control, in particular when below-ground plant parts are affected. Plant protection with beneficial soil bacteria is a promising alternative to classical chemical control. We study biocontrol strains of Pseudomonas fluorescens which colonize roots and suppress fungal plant diseases. Recently, we discovered that certain strains, besides their antifungal activity, exhibit also potent systemic and oral insecticidal activity. Anti-insect action depends on the production of a novel large protein toxin, which we termed Fit for P. fluorescens insecticidal toxin, and to additional yet unidentified bacterial factors. Fit is related to some extent to the Mcf insect toxins of the entomopathogen Photorhabdus. Fit toxin-negative mutants of P. fluorescens are less virulent when injected into insect larvae and non-toxic Escherichia coli can be rendered lethal to insects by transgenic expression of the toxin gene. The Fit toxin gene is part of a genomic region encoding three regulatory proteins and a type I protein secretion system predicted to function in toxin export. First findings suggest that the three regulators interact among each other and with known global regulators of biocontrol factor expression to control Fit toxin expression and transport. To further explore the potential of plant-associated insecticidal pseudomonads as biocontrol agents, we tested their activity in feeding assays. Fit toxin-producing pseudomonads sprayed on leaves exhibited strong oral activity towards select plant-feeding insect larvae in a dose-dependent manner. Toxin-deficient strains showed reduced activity towards the tested larvae. An extensive survey of the occurrence and molecular diversity of the insect toxin locus in a collection of root-associated pseudomonads isolated from different soils world-wide indicates that the toxin cluster occurs only in specific subgroups of these bacteria that include strains producing antifungal compounds and exhibiting suppressive activity against root diseases. Our discovery of potent oral anti-insect activity in plant-beneficial pseudomonads makes a significant contribution to the main objective of COST action 862 and opens new possibilities for microbial pest and disease control, since these bacteria are very efficient below-ground plant parts colonizers (in contrast to Bacillus thuringiensis) and they need no vector to perform (in contrast to the nematode endosymbiont Photorhabdus).

References in databases (English)

Swiss Database: COST-DB of the State Secretariat for Education and Research Hallwylstrasse 4 CH-3003 Berne, Switzerland Tel. [phone] Swiss Project-Number: C07.0026