Can Simpson's paradox explain co-operation in Pseudomonas aeruginosa biofilms?
Can Simpson's paradox explain co-operation in Pseudomonas aeruginosa biofilms?
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DOI：
10.1111/j.1574-695x.2012.00970.x
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发表时间：
2012-07-01
影响因子：
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通讯作者：
Webb, Jeremy S.
中科院分区：
文献类型：
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作者：
Penn, Alexandra S.;Conibear, Tim C. R.;Webb, Jeremy S.
生物膜中的细菌通常会表现出合作行为，例如公共产品的生产，并且可以增强它们在环境或临床环境中的生存能力。非合作作弊通常会出现，并且从理论上讲应该会破坏合作行为。因此，它的稳定性需要解释，但尚未通过实验证明抑制生物膜内作弊的机制。从理论上讲，重复聚集成组，交织着分散和重新混合，可以通过辛普森悖论增加合作。也就是说，尽管组内比例下降，但通过群体的差异增长，全球合作者的比例却有所增加。我们研究了这样的假设：微菌落的形成和扩散产生了辛普森悖论，该悖论解释了生物膜中的细菌合作。使用铜绿假单胞菌中铁载体的产生作为我们的合作模型系统，我们使用有据可查的合作者和铁载体缺陷的作弊菌株来测量合作和作弊个体的频率，原位微菌落结构内。我们检测到显着的类型内负密度依赖性效应，该效应随微菌落发育而变化。然而，我们没有发现辛普森悖论的证据。相反，我们看到了清晰的微群体内部空间结构（占据微群体内部的作弊行为），这可能违反了辛普森悖论所需的假设，即群体成员平等分享公共利益。
Co-operative behaviours, such as the production of public goods, are commonly displayed by bacteria in biofilms and can enhance their ability to survive in environmental or clinical settings. Non-co-operative cheats commonly arise and should, theoretically, disrupt co-operative behaviour. Its stability therefore requires explanation, but no mechanisms to suppress cheating within biofilms have yet been demonstrated experimentally. Theoretically, repeated aggregation into groups, interleaved with dispersal and remixing, can increase co-operation via a Simpson's paradox. That is, an increase in the global proportion of co-operators despite a decrease in within-group proportions, via differential growth of groups. We investigate the hypothesis that microcolony formation and dispersal produces a Simpson's paradox that explains bacterial co-operation in biofilms. Using the production of siderophores in Pseudomonas aeruginosa as our model system for co-operation, we use well-documented co-operator and siderophore-deficient cheat strains to measure the frequency of co-operating and cheating individuals, in-situ within-microcolony structures. We detected significant within-type negative density-dependant effects that vary over microcolony development. However, we find no evidence of Simpson's paradox. Instead, we see clear within-microcolony spatial structure (cheats occupying the interior portions of microcolonies) that may violate the assumption required for Simpson's paradox that group members share equally in the public good.