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 activity of the PA2652 chemoreceptor of Pseudomonas aeruginosa is controlled by chemoattractants and antagonists

Martín-Mora et al. Scientific Reports (2018) 8: 2102


The PA2652 chemoreceptor was shown previously to mediate chemotaxis to malate (Alvarez-Ortega & Harwood (2007) Appl Environ Microbiol. 73:7793). We have generated the recombinant ligand binding domain (LBD) of this receptor and have submitted it to high throughput ligand screens using the thermal shift assay (Krell (2015) Mol Microbiol. 96:685). In addition to malate, four other ligands were identified which are shown below.

Although methylsuccinic and citraconic acid bound to the receptor, both compounds did not elicit any chemotactic response. ITC studies revealed the both of these compounds competed in vitro with the three chemoattractants for binding at PA2652-LBD. This competition was also observed in vivo where increasing amounts of both methylsuccinic and citraconic acid, reduced malate chemotaxis (see below). In a control experiment the addition of both antagonists did not reduce chemotaxis to amino acids that is mediated by different chemoreceptors, excluding the possibility that the effect of the antagonists is due to a non-specific interference with bacterial motility. The identification of antagonists thus offers the possibility to specifically interfere and inhibit chemotaxis. This work has been published in Martín-Mora et al. (2018) Sci. Rep. (put the link when available).

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. (2017) 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.