Earth and Life Institute, Biodiversity Research Centre, Université catholique de Louvain, Louvain-la-Neuve, Belgium
Earth and Life Institute, Biodiversity Research Centre, Université catholique de Louvain, Louvain-la-Neuve, Belgium.
Appl Environ Microbiol. 2019 May 2;85(10). doi: 10.1128/AEM.02445-18. Print 2019 May 15.
Symbiotic microorganisms are widespread in nature and can play a major role in the ecology and evolution of animals. The aphid- bacterium interaction provides a valuable model to study the mechanisms behind these symbiotic associations. The recent discovery of cultivable strains with a free-living lifestyle allowed us to simulate their environmental acquisition by aphids to examine the mechanisms involved in this infection pathway. Here, after oral ingestion, we analyzed the infection dynamics of cultivable during the host's lifetime using quantitative PCR and fluorescence techniques and determined the immediate fitness consequences of these bacteria on their new host. We further examined the transmission behavior and phylogenetic position of cultivable strains. Our study revealed that cultivable bacteria are predisposed to establish a symbiotic association with a new aphid host, settling in its gut. We show that cultivable bacteria colonize the entire aphid digestive tract following infection, after which the bacteria multiply exponentially during aphid development. Our results further reveal that gut colonization by the bacteria induces a fitness cost to their hosts. Nevertheless, it appeared that the bacteria also offer an immediate protection against parasitoids. Interestingly, cultivable strains seem to be extracellularly transmitted, possibly through the honeydew, while is generally considered a maternally transmitted bacterium living within the aphid body cavity and bringing some benefits to its hosts, despite its costs. These findings provide new insights into the nature of symbiosis in aphids and the mechanisms underpinning these interactions. is one of the most common symbionts among aphid populations and includes a wide variety of strains whose degree of interdependence on the host may vary considerably. strains with a free-living capacity have recently been isolated from aphids. By using these strains, we established artificial associations by simulating new bacterial acquisitions involved in aphid gut infections to decipher their infection processes and biological effects on their new hosts. Our results showed the early stages involved in this route of infection. So far, has been considered a maternally transmitted aphid endosymbiont. Nevertheless, we show that our cultivable strains occupy and replicate in the aphid gut and seem to be transmitted over generations through an environmental transmission mechanism. Moreover, cultivable bacteria are both parasites and mutualists given the context, as are many aphid endosymbionts. Our findings give new perception of the associations involved in bacterial mutualism in aphids.
共生微生物广泛存在于自然界中，在动物的生态和进化中起着重要作用。蚜虫-细菌相互作用为研究这些共生关系背后的机制提供了一个有价值的模型。最近发现可培养的具有自由生活方式的菌株，使我们能够模拟它们被蚜虫获得的环境，以研究这种感染途径所涉及的机制。在这里，我们在口服摄入后，使用定量 PCR 和荧光技术分析了可培养菌株在宿主生命周期内的感染动态，并确定了这些细菌对新宿主的即时适应后果。我们进一步研究了可培养菌株的传播行为和系统发育位置。我们的研究表明，可培养细菌容易与新的蚜虫宿主建立共生关系，并定居在其肠道中。我们表明，可培养细菌在感染后会在蚜虫的整个消化道中定殖，然后在蚜虫发育过程中呈指数级繁殖。我们的结果进一步表明，细菌对宿主的肠道定殖会导致其适应度降低。然而，似乎细菌也为其宿主提供了即时的保护，免受寄生虫的侵害。有趣的是，可培养菌株似乎是通过蜜露进行体外传播的，而 通常被认为是一种母系传递的细菌，生活在蚜虫的体腔中，并为其宿主带来一些好处，尽管也有代价。这些发现为蚜虫共生的本质以及这些相互作用的机制提供了新的见解。是蚜虫种群中最常见的共生体之一，包括多种菌株，它们对宿主的依存度可能有很大差异。最近已经从蚜虫中分离出具有自由生活能力的 菌株。通过使用这些菌株，我们通过模拟涉及蚜虫肠道感染的新细菌获得来建立人工共生关系，以破译它们的感染过程及其对新宿主的生物学影响。我们的结果显示了这种感染途径的早期阶段。到目前为止， 一直被认为是一种母系传递的蚜虫内共生体。然而，我们表明，我们可培养的 菌株占据并在蚜虫的肠道中复制，并通过环境传播机制在几代中传播。此外，在这种情况下，可培养的 细菌既是寄生虫又是互惠共生体，就像许多蚜虫内共生体一样。我们的发现为蚜虫中细菌共生关系提供了新的认识。
