Department of Biomolecular Engineering, University of California Santa Cruz, Santa Cruz, California, United States of America.
Genomics Institute, University of California Santa Cruz, Santa Cruz, California, United States of America.
PLoS Pathog. 2024 Jul 25;20(7):e1012149. doi: 10.1371/journal.ppat.1012149. eCollection 2024 Jul.
The intracellular symbiont Wolbachia pipientis evolved after the divergence of arthropods and nematodes, but it reached high prevalence in many of these taxa through its abilities to infect new hosts and their germlines. Some strains exhibit long-term patterns of co-evolution with their hosts, while other strains are capable of switching hosts. This makes strain selection an important factor in symbiont-based biological control. However, little is known about the ecological and evolutionary interactions that occur when a promiscuous strain colonizes an infected host. Here, we study what occurs when two strains come into contact in host cells following horizontal transmission and infection. We focus on the faithful wMel strain from Drosophila melanogaster and the promiscuous wRi strain from Drosophila simulans using an in vitro cell culture system with multiple host cell types and combinatorial infection states. Mixing D. melanogaster cell lines stably infected with wMel and wRi revealed that wMel outcompetes wRi quickly and reproducibly. Furthermore, wMel was able to competitively exclude wRi even from minuscule starting quantities, indicating that this is a nearly deterministic outcome, independent of the starting infection frequency. This competitive advantage was not exclusive to wMel's native D. melanogaster cell background, as wMel also outgrew wRi in D. simulans cells. Overall, wRi is less adept at in vitro growth and survival than wMel and its in vivo state, revealing differences between the two strains in cellular and humoral regulation. These attributes may underlie the observed low rate of mixed infections in nature and the relatively rare rate of host-switching in most strains. Our in vitro experimental framework for estimating cellular growth dynamics of Wolbachia strains in different host species and cell types provides the first strategy for parameterizing endosymbiont and host cell biology at high resolution. This toolset will be crucial to our application of these bacteria as biological control agents in novel hosts and ecosystems.
细胞内共生菌沃尔巴克氏体（Wolbachia pipientis）在节肢动物和线虫分化后进化而来，但它通过感染新宿主及其生殖细胞的能力，在许多这些类群中达到了高流行率。一些菌株与宿主表现出长期的共同进化模式，而其他菌株则能够切换宿主。这使得菌株选择成为基于共生菌的生物控制的重要因素。然而，对于一个混杂菌株殖民感染宿主时发生的生态和进化相互作用，我们知之甚少。在这里，我们研究了当两种菌株通过水平传播和感染进入宿主细胞时会发生什么。我们使用一种具有多种宿主细胞类型和组合感染状态的体外细胞培养系统，专注于来自黑腹果蝇的忠实 wMel 菌株和来自拟果蝇的混杂 wRi 菌株。混合稳定感染 wMel 和 wRi 的黑腹果蝇细胞系表明，wMel 能够快速且可重复地胜过 wRi。此外，即使从微小的起始数量开始，wMel 也能够竞争性地排除 wRi，这表明这是一个几乎确定的结果，与起始感染频率无关。这种竞争优势不仅仅局限于 wMel 的本地黑腹果蝇细胞背景，因为 wMel 也在拟果蝇细胞中超过了 wRi。总体而言，wRi 在体外生长和存活方面不如 wMel 及其体内状态那么擅长，这揭示了两种菌株在细胞和体液调节方面的差异。这些属性可能是自然界中混合感染率低和大多数菌株中宿主转换率相对较低的原因。我们用于估计不同宿主物种和细胞类型中沃尔巴克氏体菌株细胞生长动态的体外实验框架，为高分辨率参数化内共生体和宿主细胞生物学提供了第一个策略。这个工具集对于我们将这些细菌作为新型宿主和生态系统中的生物控制剂的应用至关重要。
