Pseudomonas aeruginosa Performs Chemotaxis to the Neurotransmitters Serotonin, Dopamine, Epinephrine and Norepinephrine

Abstract

Bacteria use chemotaxis to move to favourable ecological niches. For many pathogenic bacteria, chemotaxis is required for full virulence, particularly for the initiation of host colonisation. There do not appear to be limits to the type of compounds that attract bacteria, and we are just beginning to understand how chemotaxis adapts them to their lifestyles. Quantitative capillary assays for chemotaxis show that P. aeruginosa is strongly attracted to serotonin, dopamine, epinephrine and norepinephrine. Chemotaxis to these compounds is greatly decreased in a mutant lacking the TlpQ chemoreceptor, and complementation of this mutant with a plasmid harbouring the tlpQ gene restores wild-type-like chemotaxis. Microcalorimetric titrations of the TlpQ sensor domain with these four compounds indicate that they bind directly to TlpQ. All four compounds are hormones and neurotransmitters that control a variety of processes and are also important signal molecules involved in the virulence of P. aeruginosa. They modulate motility, biofilm formation, the production of virulence factors and serve as siderophores that chelate iron. Additionally, this is the first report of bacterial chemotaxis to serotonin. This study provides an incentive for research to define the contribution of chemotaxis to these host signalling molecules to the virulence of P. aeruginosa.

Keywords: Pseudomonas aeruginosa; catecholamine; chemoreceptor; chemotaxis.

FIGURE 1

Chemotactic responses to dopamine, epinephrine, serotonin and norepinephrine of Pseudomonas aeruginosa PAO1. (a) Quantitative capillary chemotaxis assays of the wild‐type strain to different chemoeffector concentrations. Data were corrected for the number of bacteria that swam into buffer‐containing capillaries (3107 ± 821). (b) Responses to 5 mM of these four neurotransmitters by the wild‐type strain, the ΔtlpQ mutant and the ΔtlpQ mutant complemented with the ptlpQ plasmid. Data were corrected for the number of bacteria that swam into buffer‐containing capillaries (4071 ± 1536 for wt; 4143 ± 604 for ΔtlpQ and 2071 ± 371 for ΔtlpQ‐ptlpQ). Data are the means and standard deviations from at least three biological replicates conducted in triplicate. *Student's t‐test p < 0.01. The construction of the tlpQ deletion mutant and the plasmid ptlpQ for mutant complementation have been reported in (Corral‐Lugo et al. 2018) and (Kim et al. 2007), respectively.

FIGURE 2

Microcalorimetric titrations of dopamine, epinephrine, serotonin and norepinephrine to the TlpQ‐LBD. (a) Titration of 80 μM TlpQ‐LBD with aliquots of 10 mM dopamine. (b) Titration of 40 μM TlpQ‐LBD with aliquots of 10 mM epinephrine. (c) Competition assays: Titration of 18 μM TlpQ‐LBD with aliquots of 250 μM spermidine (Spe) in the absence and presence of 10 mM serotonin (Ser) or norepinephrine (Noe). Protein and ligand solutions were in 3 mM Tris, 3 mM PIPES, 3 mM MES, 150 mM NaCl, 10% (v/v) glycerol, pH 7.0. Experiments were conducted on a VP‐microcalorimeter (Microcal, Amherst, MA, USA) at 25°C (for dopamine) and at 10°C (for remaining compounds). Upper panels: Raw titration data. Lower panels: Integrated, concentration‐normalised and dilution‐heat‐corrected raw data fitted with the ‘one‐binding‐site’ model of the MicroCal version of ORIGIN (Microcal, Amherst, MA, USA). The corresponding binding parameters are shown in Table S1. (d) Structure of the TlpQ ligands identified.