Biofilms are closely packed cells held and shielded by extracellular matrix composed of structural proteins and exopolysaccharides (EPS). As matrix components are costly to produce and shared within the population, EPS-deficient cells can act as cheaters by gaining benefits from the cooperative nature of EPS producers. Remarkably, genetically programmed EPS producers can also exhibit phenotypic heterogeneity at single-cell level. Previous studies have shown that spatial structure of biofilms limits the spread of cheaters, but the long-term influence of cheating on biofilm evolution is not well understood. Here, we examine the influence of EPS nonproducers on evolution of matrix production within the populations of EPS producers in a model biofilm-forming bacterium, Bacillus subtilis. We discovered that general adaptation to biofilm lifestyle leads to an increase in phenotypical heterogeneity of eps expression. However, prolonged exposure to EPS-deficient cheaters may result in different adaptive strategy, where eps expression increases uniformly within the population. We propose a molecular mechanism behind such adaptive strategy and demonstrate how it can benefit the EPS producers in the presence of cheaters. This study provides additional insights on how biofilms adapt and respond to stress caused by exploitation in long-term scenario.

生物膜是紧密堆积的细胞，由结构蛋白和胞外多糖（EPS）组成的细胞外基质保持和屏蔽。由于基质成分的生产成本高昂并在人群中共享，因此，EPS缺陷细胞可以通过从EPS生产者的合作性质中受益而充当骗子。值得注意的是，经过基因编程的EPS生产商还可以在单​​细胞水平上表现出表型异质性。以前的研究表明，生物膜的空间结构限制了作弊者的传播，但是对作弊对生物膜进化的长期影响尚不十分了解。在这里，我们检查了EPS非生产者对模型生物膜形成细菌枯草芽孢杆菌中EPS生产者群体内基质生产演变的影响。。我们发现，对生物膜生活方式的普遍适应会导致eps表达的表型异质性增加。但是，长时间暴露于EPS缺陷的作弊者可能会导致采取不同的适应策略，其中EPS表达在种群内均匀增加。我们提出了这种自适应策略背后的分子机制，并展示了它在作弊者的存在下如何使EPS生产者受益。这项研究提供了关于生物膜如何适应和应对长期开采中的压力的​​更多见解。