5/3/2023 0 Comments Freespace 2 cheatsQS is the process by which small diffusible signalling molecules are released, accumulate, and when they reach a sufficient concentration, drive the expression of genes coding for extracellular factors. In this species, the production of many extracellular factors, including those involved in biofilm formation, are controlled by quorum-sensing (QS). Biofilms are thought to play a key role in the ability of this species to tolerate antibiotics and survive within long-term chronic infections in the lungs of humans with cystic fibrosis, where it is an important cause of morbidity and mortality. We use the bacterium Pseudomonas aeruginosa, an opportunistic, multi-antibiotic-resistant pathogen of plants and animals (including humans). Here we examine the fitness consequences of cheating at the population level, and test whether this varies between planktonic and biofilm populations. There are a number of reasons why this could either increase or decrease the consequences of cheating, for example by facilitating the sharing of public goods, or by keeping cheats and cooperators segregated. It is likely that biofilms change the nature of social interactions between cells, because they lead to structured and densely packed populations, with considerable potential for both competition and cooperation between cells. Biofilms are relevant to clinical environments because they are thought to play a key role in the ability of organisms to tolerate antibiotics and persist in long-term chronic infections. The relevance of such studies may be limited by the fact that the vast majority of natural bacterial populations are thought instead to exist as slimy, well-structured multicellular communities, termed biofilms. However, previous work on cooperation and cheating in bacteria has mainly focused on cells growing in planktonic liquid cultures. A clear prediction is that measures of group success, such as growth or productivity, will be negatively correlated with the proportion of cheats, as has been found in a number of studies with bacteria and other microbes. This problem, sometimes referred to as the ‘public goods dilemma’, is general to all biological populations where cooperation enhances population fitness, because while a group of individuals would benefit from cooperation, cooperation may not be stable if individuals can gain from pursuing their own selfish interests. These factors provide a benefit to the local population of cells, and so their production is potentially vulnerable to exploitation by ‘cheats’ that avoid the cost of producing them, while benefiting from those produced by others. The growth and success of bacterial populations depends upon the production of extracellular factors that are secreted to perform many functions such as nutrient acquisition, protection from the environment and the creation of enemy-free space. Finally, we discuss the clinical implications that arise from altering the susceptibility to antibiotics. Our results provide clear support that conflict over public goods reduces population fitness in bacterial biofilms, and that this effect is greater than in planktonic populations. We found that: (i) QS cheating occurs in biofilm populations owing to exploitation of QS-regulated public goods (ii) the thickness and density of biofilms was reduced by the presence of non-cooperative cheats (iii) population growth was reduced by the presence of cheats, and this reduction was greater in biofilms than in planktonic populations (iv) the susceptibility of biofilms to antibiotics was increased by the presence of cheats and (v) coercing cooperator cells to increase their level of cooperation decreases the extent to which the presence of cheats reduces population productivity. We tested this idea in the opportunistic bacterial pathogen, Pseudomonas aeruginosa, by examining the influence of putative cheats that do not cooperate via cell-to-cell signalling (quorum-sensing, QS). The idea from human societies that self-interest can lead to a breakdown of cooperation at the group level is sometimes termed the public goods dilemma.
0 Comments
Leave a Reply. |