Department of Biology, University of Oxford, Oxford, UK.
Department of Biochemistry, University of Oxford, Oxford, UK.
Nat Ecol Evol. 2023 Dec;7(12):2080-2091. doi: 10.1038/s41559-023-02234-2. Epub 2023 Nov 30.
Bacteria possess a diverse range of mechanisms for inhibiting competitors, including bacteriocins, tailocins, type VI secretion systems and contact-dependent inhibition (CDI). Why bacteria have evolved such a wide array of weapon systems remains a mystery. Here we develop an agent-based model to compare short-range weapons that require cell-cell contact, with long-range weapons that rely on diffusion. Our model predicts that contact weapons are useful when an attacking strain is outnumbered, facilitating invasion and establishment. By contrast, ranged weapons tend to be effective only when attackers are abundant. We test our predictions with the opportunistic pathogen Pseudomonas aeruginosa, which naturally carries multiple weapons, including CDI and diffusing tailocins. As predicted, short-range CDI can function at low and high frequencies, while long-range tailocins require high frequency and cell density to function effectively. Head-to-head competition experiments with the two weapon types further support our predictions: a tailocin attacker defeats CDI only when it is numerically dominant, but then we find it can be devastating. Finally, we show that the two weapons work well together when one strain employs both. We conclude that short- and long-range weapons serve different functions and allow bacteria to fight both as individuals and as a group.
细菌拥有多种抑制竞争对手的机制，包括细菌素、尾噬菌体毒素、VI 型分泌系统和接触依赖性抑制（CDI）。为什么细菌进化出如此广泛的武器系统仍然是个谜。在这里，我们开发了一个基于代理的模型，将需要细胞间接触的短程武器与依赖扩散的远程武器进行比较。我们的模型预测，当攻击菌株数量较少时，接触武器很有用，有利于入侵和建立。相比之下，只有当攻击者丰富时，远程武器才往往有效。我们用机会性病原体铜绿假单胞菌来检验我们的预测，它天然携带多种武器，包括 CDI 和扩散尾噬菌体毒素。正如预测的那样，短程 CDI 可以在低频率和高频率下发挥作用，而远程尾噬菌体毒素需要高频率和细胞密度才能有效地发挥作用。两种武器类型的直接竞争实验进一步支持了我们的预测：尾噬菌体毒素攻击者只有在数量上占优势时才能击败 CDI，但随后我们发现它可能是毁灭性的。最后，我们发现当一种菌株同时使用两种武器时，它们能很好地协同工作。我们的结论是，短程和远程武器具有不同的功能，使细菌既能个体作战，也能群体作战。
