The cuticular microbiomes of Acromyrmex leaf-cutting ants pose a conundrum in microbiome biology because they are freely colonisable, and yet the prevalence of the vertically transmitted bacteria Pseudonocardia, which contributes to the control of Escovopsis fungus garden disease, is never compromised by the secondary acquisition of other bacterial strains. Game theory suggests that competition-based screening can allow the selective recruitment of antibiotic-producing bacteria from the environment, by providing abundant resources to foment interference competition between bacterial species and by using Pseudonocardia to bias the outcome of competition in favour of antibiotic producers. Here, we use RNA-stable isotope probing (RNA-SIP) to confirm that Acromyrmex ants can maintain a range of microbial symbionts on their cuticle by supplying public resources. We then used RNA sequencing, bioassays, and competition experiments to show that vertically transmitted Pseudonocardia strains produce antibacterials that differentially reduce the growth rates of other microbes, ultimately biassing the bacterial competition to allow the selective establishment of secondary antibiotic-producing strains while excluding non-antibiotic-producing strains that would parasitise the symbiosis. Our findings are consistent with the hypothesis that competition-based screening is a plausible mechanism for maintaining the integrity of the co-adapted mutualism between the leaf-cutting ant farming symbiosis and its defensive microbiome. Our results have broader implications for explaining the stability of other complex symbioses involving horizontal acquisition.

中文翻译：

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基于竞争的筛选有助于确保防御性微生物组的进化稳定性


顶切叶蚁的表皮微生物组在微生物组生物学中提出了一个难题，因为它们可以自由定植，但垂直传播的假诺卡氏菌的流行却从未因二次获取而受到影响，这种细菌有助于控制 Escovopsis 真菌花园病。其他菌株。博弈论表明，基于竞争的筛选可以通过提供丰富的资源来煽动细菌物种之间的干扰竞争，并利用假诺卡氏菌使竞争结果偏向有利于抗生素生产者的竞争结果，从而允许从环境中选择性地招募产生抗生素的细菌。在这里，我们使用RNA稳定同位素探测（RNA-SIP）来确认Acromyrmex蚂蚁可以通过提供公共资源来维持其角质层上的一系列微生物共生体。然后，我们使用 RNA 测序、生物测定和竞争实验来表明，垂直传播的假诺卡氏菌菌株产生的抗菌剂会差异性地降低其他微生物的生长速度，最终使细菌竞争产生偏差，从而允许选择性地建立次级抗生素生产菌株，同时排除非抗生素生产菌株。产生抗生素的菌株会寄生在共生体中。我们的研究结果与以下假设相一致：基于竞争的筛选是维持切叶蚁养殖共生体与其防御性微生物组之间共同适应互利共生完整性的合理机制。我们的结果对于解释涉及水平获取的其他复杂共生体的稳定性具有更广泛的意义。