Earth and Life Institute, Biodiversity Research Centre, Université catholique de Louvain, 1348 Louvain-la-Neuve, Belgium.
FEMS Microbiol Ecol. 2022 Feb 21;98(1). doi: 10.1093/femsec/fiac012.
Symbioses are significant drivers of insect evolutionary ecology. Despite recent findings that these associations can emerge from environmentally derived bacterial precursors, there is still little information on how these potential progenitors of insect symbionts circulate in trophic systems. Serratia symbiotica represents a valuable model for deciphering evolutionary scenarios of bacterial acquisition by insects, as its diversity includes gut-associated strains that retained the ability to live independently of their hosts, representing a potential reservoir for symbioses emergence. Here, we conducted a field study to examine the distribution and diversity of S. symbiotica found in aphid populations, and in different compartments of their surrounding environment. Twenty % of aphid colonies were infected with S. symbiotica, including a wide diversity of strains with varied tissue tropism corresponding to different lifestyle. We also showed that the prevalence of S. symbiotica is influenced by seasonal temperatures. We found that S. symbiotica was present in non-aphid species and in host plants, and that its prevalence in these samples was higher when associated aphid colonies were infected. Furthermore, phylogenetic analyses suggest the existence of horizontal transfers between the different trophic levels. These results provide a new picture of the pervasiveness of an insect symbiont in nature.
共生关系是昆虫进化生态学的重要驱动因素。尽管最近的研究发现，这些共生关系可能源自环境衍生的细菌前体，但关于这些昆虫共生潜在祖先在营养系统中如何循环的信息仍然很少。共生性栖热菌代表了一个解析细菌被昆虫获取的进化情景的有价值的模型，因为它的多样性包括与肠道相关的菌株，这些菌株保留了独立于其宿主生活的能力，代表了共生出现的潜在储备库。在这里，我们进行了一项实地研究，以检查共生性栖热菌在蚜虫种群及其周围环境的不同隔室中的分布和多样性。20%的蚜虫群体感染了共生性栖热菌，包括具有不同组织嗜性的广泛多样性菌株，这些菌株对应于不同的生活方式。我们还表明，共生性栖热菌的流行受季节性温度的影响。我们发现共生性栖热菌存在于非蚜虫物种和宿主植物中，并且当相关的蚜虫群体受到感染时，这些样本中的共生性栖热菌的流行率更高。此外，系统发育分析表明，不同营养水平之间存在水平转移。这些结果提供了一个关于昆虫共生体在自然界中普遍存在的新图景。
