The Effect of a Cell-to-Cell Communication Molecule, Pseudomonas Quinolone Signal (PQS), Produced by P. aeruginosa on Other Bacterial Species

Abstract

One of the most important factors in the development of a bacterial community is whether the bacteria are able to grow in that habitat. The regulation of bacterial growth is generally studied in relation to physicochemical conditions, however, how bacterial communities regulate themselves remains unclear. In our previous study, it was demonstrated that a cell-to-cell communication molecule, 2-heptyl-3-hydroxy-4-quinolone, referred to as the Pseudomonas quinolone signal (PQS), affects respiring-activity in Pseudomonas aeruginosa without requiring its cognate receptor PqsR. The results suggested that PQS may affect other bacterial species, which was further examined in this study. PQS repressed the growth of several species including both Gram-negative and Gram-positive bacteria. In most cases, this effect differed from the bacteriostatic or bacteriolytic actions of antibiotics. The growth repression by PQS was inhibited when iron was added to the medium, indicating iron-chelating activity to be involved. In addition, PQS affected oxygen consumption in some species tested, and may have other underlying effects. Thus, this cell-to-cell communication molecule may influence the development of bacterial communities by regulating bacterial growth, and physicochemical factors such as iron would be important in determining its effect. Key words: Pseudomonas quinolone signal, cell-to-cell communication, interspecies interactionStudies of natural samples using techniques such as PCRdenaturing gradient gel electrophoresis (DGGE) and terminal-restriction fragment length polymorphism have provided information about the kinds of bacteria inhabiting different environments. However, why bacteria live where they do is still unclear. The regulation of growth is important when considering the habitats of bacteria, and many factors that regulate energy production have been studied, such as the presence of electron acceptors or electron donors and pH.Besides physicochemical factors, extracellular bacterial metabolites are also reported to control the growth of bacteria. For example, indole derivatives were isolated as growth inhibitors in Symbiobacterium thermophilum (35). Antibiotic reactions are another example of an interaction where bacterial growth is inhibited by extracellular bacterial metabolites. Recently, it has been proposed that antibiotics work as signals, regulating gene expression (8). Moreover, numerous bacteria utilize cell-to-cell communication signaling molecules, enabling them to coordinate diverse biological responses (27). In Gram-negative bacteria, these signaling molecules are typically N-acyl-L-homoserine lactones (AHLs). Pseudomonas aeruginosa is a well-studied bacterium possessing at least two AHL-dependent quorum-sensing systems, the LasR-LasI (las) and the RhlR-RhlI (rhl) systems (24). In addition, a non-AHL quorum-sensing signal, 2-heptyl-3-hydroxy-4-quinolone, referred to as the Pseudomonas quinolone signal (PQS), was found in P. aeruginosa (25). PQS regulates the production of virulence factors such as...

Pseudomonas Quinolone Signal Affects Membrane Vesicle Production in not only Gram-Negative but also Gram-Positive Bacteria

“…Although the growth of E. coli was repressed at 50 µM PQS, it recovered with the addition of FeCl 3 (final concentration, 20 µM) (data not shown), suggesting the repression to be due to iron-chelating activity of PQS. This result is consistent with a recently published study (38). PQS enhanced MV production in a dose-dependent manner up to a concentration of 20 µM and production was constant at concentrations not less than 20 µM PQS (Fig.…”

“…PQS also has iron-chelating activity (3,8) and represses the growth of other bacterial species (38). In addition, PQS positively regulates several virulence factors in P. aeruginosa (6), and virulence factors under its control have lytic activities against Gram-positive bacteria (23,30).…”

“…However, quorum-sensing signals have the potential to alter phenotypes of other bacterial species, which do not possess their receptors (38,42). In this study, we investigated the effects of PQS on MV production in both Gram-negative and -positive bacteria.…”

A Great Leap forward in Microbial Ecology

“…Indeed, PQS affects the growth of a broad spectrum of bacteria from Gram-negative to Gram-positive bacteria (159). While PQS represses the consumption of oxygen in some bacteria, the mechanism by which it represses growth is still unknown.…”

“…Several mechanisms may be involved in this growth repression since PQS has been reported to chelate iron and produce oxidative stress (12, 26, 52) besides affecting respiratory enzymatic activity. Nevertheless, the concentration of iron is a key factor in determining the effect of PQS on respiratory activity and growth indicating that the surrounding conditions control the interspecies interaction (157,159). By tuning signal production in response to the environment, bacteria could be more flexible in coping with neighboring bacteria according to the change in the environment.…”