The Pseudomonas Quinolone Signal (PQS) Balances Life and Death in Pseudomonas aeruginosa Populations

Abstract

When environmental conditions deteriorate and become inhospitable, generic survival strategies for populations of bacteria may be to enter a dormant state that slows down metabolism, to develop a general tolerance to hostile parameters that characterize the habitat, and to impose a regime to eliminate damaged members. Here, we provide evidence that the pseudomonas quinolone signal (PQS) mediates induction of all of these phenotypes. For individual cells, PQS, an interbacterial signaling molecule of Pseudomonas aeruginosa, has both deleterious and beneficial activities: on the one hand, it acts as a pro-oxidant and sensitizes the bacteria towards oxidative and other stresses and, on the other, it efficiently induces a protective anti-oxidative stress response. We propose that this dual function fragments populations into less and more stress tolerant members which respond differentially to developing stresses in deteriorating habitats. This suggests that a little poison may be generically beneficial to populations, in promoting survival of the fittest, and in contributing to bacterial multi-cellular behavior. It further identifies PQS as an essential mediator of the shaping of the population structure of Pseudomonas and of its response to and survival in hostile environmental conditions. A little poison may be generically beneficial to bacterial populations. By eliminating damaged members and by promoting survival of the fittest, selective poisoning may significantly contribute to multi-cellular bacterial behavior. Here, we report that the pseudomonas quinolone signal (PQS) exhibits both beneficial and deleterious activities and propose that pro- and anti-oxidant effects fragment the population into less and more stress tolerant members. We suggest our findings point to PQS as a cellular “trainer” whose role is to mediate selection of the fittest through a “make or break” mechanism. PQS thereby issues decisions on life and death in Pseudomonas aeruginosa populations, and may be essential in shaping the population structure, contributing to multi-cellular development processes in bacterial biofilms, and helping to maintain discrete, ordered spatial structures.