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Quorum sensing and bacterial social interactions in biofilms.

Li YH, Tian X - Sensors (Basel) (2012)

Bottom Line: Many bacteria are known to regulate their cooperative activities and physiological processes through a mechanism called quorum sensing (QS), in which bacterial cells communicate with each other by releasing, sensing and responding to small diffusible signal molecules.The ability of bacteria to communicate and behave as a group for social interactions like a multi-cellular organism has provided significant benefits to bacteria in host colonization, formation of biofilms, defense against competitors, and adaptation to changing environments.Therefore, understanding the molecular details of quorum sensing mechanisms and their controlled social activities may open a new avenue for controlling bacterial infections.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology and Immunology, Dalhousie University, Halifax, NS, Canada. yung-hua.li@dal.ca

ABSTRACT
Many bacteria are known to regulate their cooperative activities and physiological processes through a mechanism called quorum sensing (QS), in which bacterial cells communicate with each other by releasing, sensing and responding to small diffusible signal molecules. The ability of bacteria to communicate and behave as a group for social interactions like a multi-cellular organism has provided significant benefits to bacteria in host colonization, formation of biofilms, defense against competitors, and adaptation to changing environments. Importantly, many QS-controlled activities have been involved in the virulence and pathogenic potential of bacteria. Therefore, understanding the molecular details of quorum sensing mechanisms and their controlled social activities may open a new avenue for controlling bacterial infections.

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Related in: MedlinePlus

A schematic diagram describing quorum sensing-mediated social cooperation and conflict. Social cooperation provides benefits to the population but has a cost for the cooperative cells. Cooperative cells provide fitness benefits to the entire population (A) and have a higher productivity or yield in an exoproduct (B). However, non-cooperative cells (cheaters) may have the lower productivity (C), but can exploit the benefits from the cooperative cells without contribution in mixed populations (D).
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f3-sensors-12-02519: A schematic diagram describing quorum sensing-mediated social cooperation and conflict. Social cooperation provides benefits to the population but has a cost for the cooperative cells. Cooperative cells provide fitness benefits to the entire population (A) and have a higher productivity or yield in an exoproduct (B). However, non-cooperative cells (cheaters) may have the lower productivity (C), but can exploit the benefits from the cooperative cells without contribution in mixed populations (D).

Mentions: From an evolutionary point of view, however, bacterial social behavior may create conflict of interest and even potential risk to the population, because evolutionary theory predicts that individuals that cooperate can be exploited by selfish individuals or “cheaters” that do not cooperate but obtain the benefit from cooperators [65–67,69]. The advantage of cooperation is easy to understand if populations are monoclonal and the fitness cost to individual cells is outweighed by the benefit to the population. However, in many realistic situations microbial populations are not monoclonal but rather heterogeneous populations where cooperators and non-cooperators interact. Cooperation provides fitness benefits or “public goods” to the population, but the population benefits often come at a cost to individuals [65–70]. The question then arises as to why individuals produce costly public goods if these increase the fitness of other individual at their own cost. This is a conflict of interest between the fitness of individuals and the fitness of the group. The basis for explanation of such cooperation is provided by Hamilton’s inclusive fitness or Kin selection theory, which states that cooperation evolves between genetically related individuals or relatives [66]. A good illustration of this conflict is the trade-off between slow growth rates with a high yield versus fast but wasteful growth. Higher yields make a more economic use of limited resources and, therefore, can be beneficial to the entire population (Figure 3). The population benefit comes at the expense of individual-level restraint, as cells could grow faster with lower yields [67]. Another example is the persister phenotype, which has a role in bacterial antibiotic resistance. Persisters are cells in a dormant state that typically compose a small fraction of all cells in a population. As many antibiotics act on growing cells, dormant cell can resist short treatments and afterwards revert back to active growth to restore the population. The persister phenotype is therefore a bet-hedging strategy that confers antibiotic resistance, but does so at the cost of the growth by entering the dormant state [67]. The emergence of non-cooperators through mutation is a major challenge to cooperative phenotypes. Diggle et al. observed this effect in quorum-sensing populations of the opportunistic pathogen P. aeruginosa [65]. They found that quorum sensing provided a benefit at the group level, but exploitative individuals could avoid the cost of producing the QS signal (signal negative mutant) or of performing the cooperative behavior that was coordinated by QS (signal-blind mutant). These non-cooperators can therefore spread in the population. These researchers also showed a solution to this problem of exploitation by kin selection, which might be highly important in microbial social behaviors because of their clonal reproduction and relatively local interactions [65]. Natural biofilms in many environments are often characterized by high cell density and high diversity of microbial species. The biofim community allows close cell-cell interactions within or between species, resulting in inevitable intra- and inter-species interactions, including both cooperation and competitions [17–21]. These interactions may play very important roles in maintaining homeostasis of microbes in a biofilm community [17,19]. The diversity and interactions that can arise in biofilms represent unique opportunity for testing ecological and evolutionary theories.


Quorum sensing and bacterial social interactions in biofilms.

Li YH, Tian X - Sensors (Basel) (2012)

A schematic diagram describing quorum sensing-mediated social cooperation and conflict. Social cooperation provides benefits to the population but has a cost for the cooperative cells. Cooperative cells provide fitness benefits to the entire population (A) and have a higher productivity or yield in an exoproduct (B). However, non-cooperative cells (cheaters) may have the lower productivity (C), but can exploit the benefits from the cooperative cells without contribution in mixed populations (D).
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3376616&req=5

f3-sensors-12-02519: A schematic diagram describing quorum sensing-mediated social cooperation and conflict. Social cooperation provides benefits to the population but has a cost for the cooperative cells. Cooperative cells provide fitness benefits to the entire population (A) and have a higher productivity or yield in an exoproduct (B). However, non-cooperative cells (cheaters) may have the lower productivity (C), but can exploit the benefits from the cooperative cells without contribution in mixed populations (D).
Mentions: From an evolutionary point of view, however, bacterial social behavior may create conflict of interest and even potential risk to the population, because evolutionary theory predicts that individuals that cooperate can be exploited by selfish individuals or “cheaters” that do not cooperate but obtain the benefit from cooperators [65–67,69]. The advantage of cooperation is easy to understand if populations are monoclonal and the fitness cost to individual cells is outweighed by the benefit to the population. However, in many realistic situations microbial populations are not monoclonal but rather heterogeneous populations where cooperators and non-cooperators interact. Cooperation provides fitness benefits or “public goods” to the population, but the population benefits often come at a cost to individuals [65–70]. The question then arises as to why individuals produce costly public goods if these increase the fitness of other individual at their own cost. This is a conflict of interest between the fitness of individuals and the fitness of the group. The basis for explanation of such cooperation is provided by Hamilton’s inclusive fitness or Kin selection theory, which states that cooperation evolves between genetically related individuals or relatives [66]. A good illustration of this conflict is the trade-off between slow growth rates with a high yield versus fast but wasteful growth. Higher yields make a more economic use of limited resources and, therefore, can be beneficial to the entire population (Figure 3). The population benefit comes at the expense of individual-level restraint, as cells could grow faster with lower yields [67]. Another example is the persister phenotype, which has a role in bacterial antibiotic resistance. Persisters are cells in a dormant state that typically compose a small fraction of all cells in a population. As many antibiotics act on growing cells, dormant cell can resist short treatments and afterwards revert back to active growth to restore the population. The persister phenotype is therefore a bet-hedging strategy that confers antibiotic resistance, but does so at the cost of the growth by entering the dormant state [67]. The emergence of non-cooperators through mutation is a major challenge to cooperative phenotypes. Diggle et al. observed this effect in quorum-sensing populations of the opportunistic pathogen P. aeruginosa [65]. They found that quorum sensing provided a benefit at the group level, but exploitative individuals could avoid the cost of producing the QS signal (signal negative mutant) or of performing the cooperative behavior that was coordinated by QS (signal-blind mutant). These non-cooperators can therefore spread in the population. These researchers also showed a solution to this problem of exploitation by kin selection, which might be highly important in microbial social behaviors because of their clonal reproduction and relatively local interactions [65]. Natural biofilms in many environments are often characterized by high cell density and high diversity of microbial species. The biofim community allows close cell-cell interactions within or between species, resulting in inevitable intra- and inter-species interactions, including both cooperation and competitions [17–21]. These interactions may play very important roles in maintaining homeostasis of microbes in a biofilm community [17,19]. The diversity and interactions that can arise in biofilms represent unique opportunity for testing ecological and evolutionary theories.

Bottom Line: Many bacteria are known to regulate their cooperative activities and physiological processes through a mechanism called quorum sensing (QS), in which bacterial cells communicate with each other by releasing, sensing and responding to small diffusible signal molecules.The ability of bacteria to communicate and behave as a group for social interactions like a multi-cellular organism has provided significant benefits to bacteria in host colonization, formation of biofilms, defense against competitors, and adaptation to changing environments.Therefore, understanding the molecular details of quorum sensing mechanisms and their controlled social activities may open a new avenue for controlling bacterial infections.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology and Immunology, Dalhousie University, Halifax, NS, Canada. yung-hua.li@dal.ca

ABSTRACT
Many bacteria are known to regulate their cooperative activities and physiological processes through a mechanism called quorum sensing (QS), in which bacterial cells communicate with each other by releasing, sensing and responding to small diffusible signal molecules. The ability of bacteria to communicate and behave as a group for social interactions like a multi-cellular organism has provided significant benefits to bacteria in host colonization, formation of biofilms, defense against competitors, and adaptation to changing environments. Importantly, many QS-controlled activities have been involved in the virulence and pathogenic potential of bacteria. Therefore, understanding the molecular details of quorum sensing mechanisms and their controlled social activities may open a new avenue for controlling bacterial infections.

Show MeSH
Related in: MedlinePlus