Plant Growth Promoting Rhizobacteria and Biodegradation
Bacteria residing in soil display a huge diversity of metabolic activities. Research in the PGPRB group explores capabilities elaborated by specific subpopulations:
- non-pathogenic pseudomonads thriving in the root environment of crop plants and exerting beneficial effects on their hosts (Plant Growth Promoting Rhizobacteria or PGPR)
- pollutant-degrading bacterial strains capable of metabolizing pesticides that contaminate agricultural soils.
Pseudomonas
Research in the PGPRB group initially focused on the involvement of outer membrane proteins in root colonization by Pseudomonas. Subsequently, other topics related to rhizosphere competence, such as chemotactic attraction to root exudates, were addressed. In vivo expression technology (IVET) was used to identify other Pseudomonas genes that are induced or upregulated upon interaction with a host plant. Current research explores antagonism among root-colonizing Pseudomonas and related bacteria, mediated by bacteriocins or secondary metabolites. Interesting novel activities were discovered in a collection of strains isolated from the root environment of various crops (banana, rice, wheat, maize) grown in different geographical areas. New insights in biosynthesis, structure, and mode of action of active substances are generated using state-of-the-art approaches in molecular microbiology, including genome analysis of producer strains. |
Genetic and (bio)chemical characterization of antibiosis by root-colonizing Pseudomonas |
Novel narrow-spectrum antibacterial Pseudomonas metabolites: Wen Li (PhD student)
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This study aims at the characterization of novel Pseudomonas putida antimicrobials affecting (phyto)pathogenic bacteria. A rice rhizosphere isolate P. putida RW10S1 produces a compound that selectively targets other Pseudomonas, including Pseudomonas aeruginosa and Pseudomonas syringae. Several phytopathogenic Xanthomonas species are inhibited by a selected P. putida strain isolated from banana rhizosphere. The secondary metabolites mediating this antagonism are being characterized. |
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Secondary metabolites antagonizing Pseudomonas savastanoi: Hassan Rokni Zadeh (PhD student)
Selected non-pathogenic fluorescent Pseudomonas strains are studied for their capacity to inhibit the growth of P. savastanoi, the causative agent of olive knot, a major disease of olive plants. Of particular interest is a P. putida strain isolated from rice rhizosphere. Apparently, this strain exhibits an antagonistic activity that it is triggered by the presence of a target strain, suggesting a novel type of interaction between bacteria. Genetic analysis combined with structural characterization of active molecules is pursued to elucidate the molecular basis of this interaction.
Detection of novel NRPS genes in Pseudomonas: Hassan Rokni Zadeh (PhD student)
Pseudomonas strains are notorious producers of various antimicrobial lipopeptides (LPs) synthesized by non-ribosomal peptide synthetase (NRPS) enzymes. Focusing on non-pathogenic plant-associated Pseudomonas, a PCR strategy was devised to detect such NRPS genes by targeting their lipoinitiation and tandem thioesterase domains, while avoiding interference from amplicons of other NRPS genes, such as those of pyoverdine siderophore biosynthesis. In addition to tracing NRPS genes in known LP producers, the method enables identification of novel LP producers among Pseudomonas isolates.
Structure and mode of action of lectin-like bacteriocins: Maarten Ghequire (PhD student)
This research project focuses on a novel type of bacteriocin that mediates antagonism among closely related strains. LlpA from P. putida BW11M1 represents the prototype of a new family of proteins with antibacterial activity. Remarkably, this protein is related to a large family of plant lectins, the so-called monocot mannose-binding lectins. In addition to the biocontrol strain P. fluorescens Pf-5, some other plant-associated bacteria like Burkholderia and Xanthomonas strains carry llpA-like genes. This project aims at the elucidation of the 3D structure and mode of action and runs in collaboration with Prof. R. Loris (Laboratory of Ultrastructure, Vrije Universiteit Brussel).
Biodegradation
A second line of research investigates the molecular mechanisms enabling soil bacteria to degrade pollutants. Previous research on biodegradation of thiocarbamate herbicides by Rhodococcus also involved the development of genetic tools for these actinomycetes. In the course of this work, the first eubacterial proteasome was discovered.
Current research runs in collaboration with Prof. D. Springael (Division of Soil and Water Management, K.U.Leuven) and focuses on genetic analysis of biodegradation of phenylurea herbicides (Karolien Bers and Pieter Albers, PhD students) and methylcarbamate insecticides (Oanh Nguyen, PhD student).
