Under iron-limiting conditions, fluorescent pseudomonads acquire iron from the environment by secreting strain-specific, iron-chelating siderophores termed pyoverdines (PVD). The rhizosphere bacterium Pseudomonas protegens Pf-5 produces its own PVD but also can cross-feed on PVDs produced by other species. Previous work has found that Pf-5 continues to produce its own PVD when allowed to cross-feed, raising questions about the benefit of heterologous PVD utilisation. Here, we investigate this question using a defined, unidirectional P. protegens Pf-5/Pseudomonas aeruginosa PAO1 cross-feeding model. Quantifying the production of PVD in the presence of heterologous PVD produced by PAO1, we show that cross-feeding Pf-5 strains reduce the production of their own PVD, while non-cross-feeding Pf-5 strains increase the production of PVD. Measuring the fitness of cross-feeding and non-cross-feeding Pf-5 strains in triple coculture with PAO1, we find that cross-feeding provides a fitness benefit to Pf-5 when the availability of heterologous PVD is high. We conclude that cross-feeding can reduce the costs of self-PVD production and may thus aid in the colonisation of iron-limited environments that contain compatible siderophores produced by other resident microbes. Taken together, these results expand our understanding of the mechanisms of interspecific competition for iron in microbial communities.

中文翻译：

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保护假单胞菌 Pf-5 与吡维丁交叉喂养的健身益处

在铁限制条件下，荧光假单胞菌通过分泌菌株特异性铁螯合铁载体（称为“pyoverdines”（PVD））从环境中获取铁。根际细菌保护假单胞菌Pf-5 产生自己的 PVD，但也可以交叉取食其他物种产生的 PVD。之前的研究发现，当允许交叉供给时，Pf-5 会继续产生自己的 PVD，这引发了关于异源 PVD ​​利用的好处的问题。在这里，我们使用定义的单向P. protegens Pf-5/铜绿假单胞菌PAO1 交叉喂养模型来研究这个问题。通过量化 PAO1 产生的异源 PVD ​​存在下的 PVD ​​产量，我们发现交叉饲喂的 Pf-5 菌株会减少其自身 PVD ​​的产量，而非交叉饲喂的 Pf-5 菌株会增加 PVD ​​的产量。通过测量交叉饲喂和非交叉饲喂 Pf-5 菌株与 PAO1 三重共培养的适应性，我们发现，当异源 PVD ​​的可用性较高时，交叉饲喂可为 Pf-5 提供适应性益处。我们得出的结论是，交叉喂养可以降低自体 PVD ​​生产的成本，因此可能有助于在含有其他常驻微生物产生的相容铁载体的铁限制环境中定殖。总而言之，这些结果扩展了我们对微生物群落中铁的种间竞争机制的理解。