Welcome to the Krell laboratory.

The Krell laboratory is part of the research group “Environmental Microbiology and Biodegradation”. The laboratory is located at the Estación Experimental del Zaidín in Granada (Spain) which is part of the Spanish National Research Council (CSIC).

The plant compound Rosmarinic acid induces a broad quorum sensing response in Pseudomonas aeruginosa

Fernández et al. (2018) Env. Microbiol

We have shown previously that rosmarinic acid (RA) binds to the RhlR quorum sensing regulator, regulates the expression from several RhlR controlled promoters, which manifests itself in several quorum sensing (QS) related phenotypes (Corral-Lugo et al. (2016) Science Signaling 409:ra1).

In Fernández et al. (2018) Env. Microbiol. we have now assessed the global effect of RA on P. aeruginosa transcript levels using RNA-seq. RA induced the expression of 128 genes, amongst which many virulence factor genes. RA triggers a broad QS response because 88% of the induced genes are known to be controlled by QS, and because RA stimulated genes were found to be involved in all four QS signaling systems within P. aeruginosa. As shown in the Figure below there was a close overlap between RA induced genes and those induced by acylhomoserine lactone ligands.

RNA-seq results were verified by promoter expression studies using lacZ fusions. As exemplified by the hcn and lasI promoters significant induction by RA and C4-HSL was observed in the wild type (not shown) and the rhlI/lasI double mutant (below). However, no induction was observed in the rhlI/lasI/rhlR triple mutant, which is consistent with the notion that regulatory effects observed are due to the RA-RhlR interaction.


Three dimensional structure of the ligand binding domain of the Pseudomonas putida polyamine receptor

Gavira et al. J Mol Biol. (2018)


We have previously identified with McpU the first chemoreceptor that binds specifically different polyamines (Corral-Lugo et al. (2016) Env. Microbiol.). We now report the three dimensional structure of the McpU ligand binding domain in complex with putrescine, which has been solved by the Gavira laboratory. It is a dCACHE domain that contains bound putrescine in the membrane distal module.

Well-defined density was observed for putrescine which allowed the precise placement of the ligand (below). Significant similarities were identified in the ligand binding mode of McpU and the Mlp37 chemoreceptor of Vibrio cholerae in complex with taurine. Both ligands possess a primary amino group that is recognized by the protein in a similar manner, namely involving an Asp/Tyr/Asp triad (below). Both ligand binding domains share only 15 % sequence identity, but this feature can potentially be used to identify sensor domains that recognize primary amines.

Identification of a plant compound that modulates Pseudomonas aeruginosa quorum sensing

Corral-Lugo et al. Science Signaling (2016) 9(409):ra1

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Bacteria communicate with each other via quorum sensing (QS) mechanisms. For many pathogens it has been shown that QS regulates the expression of virulence related genes. It is also known that plants produce and secrete compounds that interfere with pathogen QS signaling, which is considered to be a defense mechanism. However, little is known about the identity of these plant compounds. In Corral-Lugo et al. Science Signaling (2016) 9(409):ra1 (direct link) we identify rosmarinic acid (RA) as a plant compound that interferes with P. aeruginosa PAO1 QS. We show that RA binds tightly to the QS regulator RhlR and in silico docking experiments indicate that RA competes with the cognate C-4-homoserine lactone (C4-HSL) for binding.

Homology model of the RhlR effector binding domain containing RA (red) and C4-HSL (green) in their best-fit positions as determined by in silico docking experiments.

In vitro transcription assays demonstrate that RA has a higher capacity to stimulate RhlR-mediated transcription than the cognate C4-HSL.

In vitro transcription from the hcnABC promoter in the presence of RhlR as well as C4-HSL, RA and chlorogenic acid (compound structurally similar to RA that did not bind to RhlR).

Gene expression studies show that RA enhances the expression from different promoters that were previously shown to be controlled by RhlR. The addition of RA to P. aeruginosa cultures caused a number of typical QS-mediated and virulence-related phenotypes such as increases in pyocyanin and elastase production as well as a stimulation of biofilm formation.

Left: Biofilm formation in the presence of RA and chlorogenic acid. Right: Pyocyanin production (green colour) in the absence and presence of different RA concentrations.

It has been shown previously that P. aeruginosa infection causes RA secretion from plant roots and we hypothesize that the secretion of the QS agonist RA causes premature gene expression. Further work will show to what extent such premature expression modulates the efficiency of plant infection.

Selected publications

Matilla, M.A., Krell, T. (2018) The effect of bacterial chemotaxis on host infection and pathogenicity. FEMS Microbiol Rev. doi: 10.1093/femsre/fux052.

Ortega, Á., Zhulin, I.B., Krell, T. (2017) Sensory Repertoire of Bacterial Chemoreceptors. Microbiol Mol Biol Rev. doi: 10.1128/MMBR.00033-17.

Rico-Jiménez M, Reyes-Darias JA, Ortega Á, Díez Peña AI, Morel B, Krell T. (2016) Two different mechanisms mediate chemotaxis to inorganic phosphate in Pseudomonas aeruginosa. Scientific Reports 6:28967.

Corral-Lugo A, Daddaoua A, Ortega A, Espinosa-Urgel M, Krell T. (2016) Rosmarinic acid is a homoserine lactone mimic produced by plants that activates a bacterial quorum-sensing regulator. Science Signaling 9(409):ra1.

Martín-Mora D, Reyes-Darias JA, Ortega A, Corral-Lugo A, Matilla MA, Krell T. (2016) McpQ is a specific citrate chemoreceptor that responds preferentially to citrate/metal ion complexes. Environ Microbiol.  18:3284-3295.

Fernández M, Morel B, Corral-Lugo A, Krell T. (2016) Identification of a chemoreceptor that specifically mediates chemotaxis toward metabolizable purine derivatives. Mol Microbiol. 99:34-42.

Krell T. (2015) Tackling the bottleneck in bacterial signal transduction research: high-throughput identification of signal molecules. Mol. Microbiol. 96: 685-8.

Reyes-Darias JA, García V, Rico-Jiménez M, Corral-Lugo A, Lesouhaitier O, Juárez-Hernández D, Yang Y, Bi S, Feuilloley M, Muñoz-Rojas J, Sourjik V, Krell T. (2015). Specific gamma-aminobutyrate (GABA) chemotaxis in Pseudomonads with different lifestyle. Mol. Microbiol. 97:488-501.

Reyes-Darias JA, Yang Y, Sourjik V, Krell T. (2015) Correlation between signal input and output in PctA and PctB amino acid chemoreceptor of Pseudomonas aeruginosa. Mol. Microbiol. 2015. 96, 513-25.

García Fontana, C., Corral-Lugo, A., Krell, T. (2014) Specificity of the CheR2 Methyltransferase in Pseudomonas aeruginosa is Directed by C-Terminal Pentapeptides in Chemoreceptors. Science Signaling 7 (320) ra34.

Rico-Jiménez M., Muñoz-Martínez F., García-Fontana C., Fernandez M., Morel B., Ortega A., Ramos J.L., Krell T. (2013) Paralogous chemoreceptors mediate chemotaxis towards protein amino acids and the non-protein amino acid gamma-aminobutyrate (GABA). Mol. Microbiol. 88 (6): 1230-1243.

Garcia-Fontana C., Reyes-Darias J.A., Munoz-Martinez F., Alfonso C., Morel B., Ramos J.L., Krell T. (2013) High specificity in CheR methyltransferase function: CheR2 of Pseudomonas putida is essential for chemotaxis whereas CheR1 is involved in biofilm formation. J. Biol. Chem. 288 (26):18987-99.

Pineda-Molina, E., Reyes-Darias, J.A., Lacal, J., Ramos, J.L., García-Ruiz, J.M., Gavira, J.A., Krell, T. (2012) Evidence for chemoreceptors with bimodular ligand binding regions harboring two signal-binding sites. Proc. Acad. Natl. Sci. USA. 109, 18926-18931.