The path to re-evolve cooperation is constrained in Pseudomonas aeruginosa

Abstract

Background: A common form of cooperation in bacteria is based on the secretion of beneficial metabolites, shareable as public good among cells within a group. Because cooperation can be exploited by "cheating" mutants, which contribute less or nothing to the public good, there has been great interest in understanding the conditions required for cooperation to remain evolutionarily stable. In contrast, much less is known about whether cheats, once fixed in the population, are able to revert back to cooperation when conditions change. Here, we tackle this question by subjecting experimentally evolved cheats of Pseudomonas aeruginosa, partly deficient for the production of the iron-scavenging public good pyoverdine, to conditions previously shown to favor cooperation. Results: Following approximately 200 generations of experimental evolution, we screened 720 evolved clones for changes in their pyoverdine production levels. We found no evidence for the re-evolution of full cooperation, even in environments with increased spatial structure, and reduced costs of public good production -two conditions that have previously been shown to maintain cooperation. In contrast, we observed selection for complete abolishment of pyoverdine production. The patterns of complete trait degradation were likely driven by "cheating on cheats" in unstructured, iron-limited environments where pyoverdine is important for growth, and selection against a maladaptive trait in iron-rich environments where pyoverdine is superfluous.

Ecology drives the evolution of diverse social strategies in Pseudomonas aeruginosa

“…This pattern is consistent with previous studies, where nonproducing cheats spread because they used pyoverdine produced by others (Ghoul, West et al, 2014; Harrison et al, 2017; Kümmerli et al, 2015). The mutational patterns discovered are also consistent with previous work showing that pyoverdine non‐ or reduced‐production predominantly arose by mutations in pvdS and its promotor region in nonhypermutator clones (Granato & Kümmerli, 2017; Kümmerli et al, 2015; O’Brien et al, 2019; Tostado‐Islas et al, 2021). The sigma factor pvdS regulates the expression of the entire pyoverdine biosynthesis machinery (Cunliffe et al, 1995; Ringel & Brüser, 2018).…”

An overview of siderophore biosynthesis among fluorescent Pseudomonads and new insights into their complex cellular organization

“…The organization in siderosomes could play such a regulating role. Moreover, bacteria live in communities with some producing siderophores and some acting as cheater (do not produce siderophores but use those produced by other bacteria); such social interactions in communities also affect the regulation of siderophore production (Butaitė et al, 2017;Granato and Kümmerli, 2017;Butaitė et al, 2018;Özkaya et al, 2018;Stilwell et al, 2018). This question needs to be investigated further in the future at the level of diverse communities involving different Pseudomonads but also other bacterial species since P. aeruginosa is able to use many different siderophores produced by other bacteria (exosiderophores) (Cornelis and Matthijs, 2002;Cornelis and Dingemans, 2013).…”

Bacterial quorum sensing allows graded and bimodal cellular responses to variations in population density

“…(7). More recently, integration of molecular and evolutionary approaches has increased the menu of potential functions to include sensing multiple aspects of both the social and physical environment (6,(8)(9)(10) and coordinating complex social strategies that limit the profitability of non-cooperating 'cheat' strains (11)(12)(13)(14)(15)(16)(17)(18).…”