Antibiotics Research and Re-evaluation Key Laboratory of Sichuan Province, Sichuan Industrial Institute of Antibiotics, Chengdu University, No. 168, Huaguan Road, Chengdu, 610052, Sichuan, China.
School of Mathematical Sciences, University of Electronic Science and Technology of China, No. 2006, Xiyuan Avenue, Chengdu, 611731, Sichuan, China.
BMC Biol. 2019 Mar 6;17(1):20. doi: 10.1186/s12915-019-0639-3.
Microbial communities are susceptible to the public goods dilemma, whereby individuals can gain an advantage within a group by utilizing, but not sharing the cost of producing, public goods. In bacteria, the development of quorum sensing (QS) can establish a cooperation system in a population by coordinating the production of costly and sharable extracellular products (public goods). Cooperators with intact QS system and robust ability in producing public goods are vulnerable to being undermined by QS-deficient defectors that escape from QS but benefit from the cooperation of others. Although microorganisms have evolved several mechanisms to resist cheating invasion in the public goods game, it is not clear why cooperators frequently coexist with defectors and how they form a relatively stable equilibrium during evolution.
We show that in Pseudomonas aeruginosa, QS-directed social cooperation can select a conditional defection strategy prior to the emergence of QS-mutant defectors, depending on resource availability. Conditional defectors represent a QS-inactive state of wild type (cooperator) individual and can invade QS-activated cooperators by adopting a cheating strategy, and then revert to cooperating when there are abundant nutrient supplies irrespective of the exploitation of QS-mutant defector. Our mathematical modeling further demonstrates that the incorporation of conditional defection strategy into the framework of iterated public goods game with sound punishment mechanism can lead to the coexistence of cooperator, conditional defector, and defector in a rock-paper-scissors dynamics.
These findings highlight the importance of behavioral heterogeneity in stabilizing the population structure and provide a potential reasonable explanation for the maintenance and evolution of cooperation in microbial communities.
微生物群落容易受到公共物品困境的影响，即在群体中，个体可以通过利用但不共享公共物品的成本来获得优势。在细菌中，群体感应（QS）的发展可以通过协调生产昂贵且可共享的细胞外产物（公共物品）来在种群中建立合作系统。具有完整 QS 系统和生产公共物品能力强的合作者很容易被逃避 QS 但受益于他人合作的 QS 缺陷缺陷者破坏。尽管微生物已经进化出几种机制来抵抗公共物品博弈中的欺骗入侵，但尚不清楚为什么合作者经常与缺陷者共存，以及它们在进化过程中如何形成相对稳定的平衡。
我们表明，在铜绿假单胞菌中，QS 指导的社会合作可以根据资源可用性选择在 QS 突变缺陷者出现之前的条件缺陷策略。条件缺陷者代表野生型（合作者）个体的 QS 非活跃状态，并且可以通过采用欺骗策略入侵 QS 激活的合作者，然后在有丰富养分供应时恢复合作，而不管 QS 突变缺陷者的利用情况如何。我们的数学模型进一步表明，将条件缺陷策略纳入具有健全惩罚机制的迭代公共物品博弈框架中，可以导致合作者、条件缺陷者和缺陷者在石头剪刀布动态中共存。
这些发现强调了行为异质性在稳定种群结构中的重要性，并为微生物群落中合作的维持和进化提供了一个潜在的合理解释。
