Cooperation and competition in pathogenic bacteria

Abstract

Explaining altruistic cooperation is one of the greatest challenges for evolutionary biology. One solution to this problem is if costly cooperative behaviours are directed towards relatives. This idea of kin selection has been hugely influential and applied widely from microorganisms to vertebrates. However, a problem arises if there is local competition for resources, because this leads to competition between relatives, reducing selection for cooperation. Here we use an experimental evolution approach to test the effect of the scale of competition, and how it interacts with relatedness. The cooperative trait that we examine is the production of siderophores, iron-scavenging agents, in the pathogenic bacterium Pseudomonas aeruginosa. As expected, our results show that higher levels of cooperative siderophore production evolve in the higher relatedness treatments. However, our results also show that more local competition selects for lower levels of siderophore production and that there is a significant interaction between relatedness and the scale of competition, with relatedness having less effect when the scale of competition is more local. More generally, the scale of competition is likely to be of particular importance for the evolution of cooperation in microorganisms, and also the virulence of pathogenic microorganisms, because cooperative traits such as siderophore production have an important role in determining virulence.

Multiple antibiotic resistance index, fitness and virulence potential in respiratory Pseudomonas aeruginosa from Jamaica

“…West & Buckling (2003) showed that the production of pyoverdin, favoured on King B medium, was metabolically costly to the micro-organism that produced it. However, Griffin et al (2004) noted that a population of mutant P. aeruginosa strains that did not produce the siderophore declined in numbers when grown in the presence of other strains that produced it. From this study, it can be inferred that by producing pyoverdin the susceptible strain adversely affected the population of the drug-resistant strain and this explains how the susceptible strain could out-compete the resistant strains as observed in this study.…”

Evolution of cooperation and control of cheating in a social microbe

“…This is particularly true for microbes, wherein the structured environments necessary for cooperation have been discovered to be pervasive (10,19,20). Microbes are particularly affected by the actions of their neighbors, because many functions that are internal in multicellular organisms are external in single-celled organisms.…”

“…Evolutionary studies of cooperative interactions have focused on the selective advantages of cooperating, how cooperation is organized, whether cheating a cooperative system can occur, and how cheaters are controlled (4)(5)(6)(7)(8)(9)(10)(11). These studies generally, but not always, focus on within-species interactions and have been behaviorally oriented.…”

What can microbial genetics teach sociobiology?

“…These mutants outcompete wild-type cells when grown in mixtures. Similarly, strains of the pathogenic bacterium Pseudomonas aeruginosa that do not produce the siderophores that are required to scavenge insoluble iron from the environment [33,34] also fare better than wild-type cells in mixtures. In addition, in societies of the bacterium Myxococcus xanthus [19,[35][36][37] and the slime mold Dictyostelium discoideum [38], mutants have been identified that overproduce spores at the expense of other strains in the fruiting body.…”

“…The effect can be easily understood in the context of cheater mutants such as SUC2 − S. cerevisiae, which do not produce invertase [32], or strains of P. aeruginosa that fail to produce siderophores [33,34]. Only when individuals are not highly related (e.g.…”