BACKGROUND Many phytophagous insects, whose diet is generally nitrogen-poor, rely on gut bacteria to compensate for nutritional deficits. Accordingly, we hypothesized that insects in desert environments may evolve associations with gut bacteria to adapt to the extremely low nutrient availability. For this, we conducted a systematic survey of bacterial communities in the guts of weevils developing inside mud chambers affixed to plant roots in the Negev Desert of Israel, based on 16S rRNA gene amplicon sequencing. RESULTS Our analyses revealed that gut bacterial communities in weevil larvae were similar across a wide geographical range, but differed significantly from those of the mud chambers and of the surrounding soils. Nevertheless, a high proportion of bacteria (including all of the core bacteria) found in the weevils were also detected in the mud chambers and soils at low relative abundances. The genus Citrobacter (of the Enterobacteriaceae family) was the predominant group in the guts of all individual weevils. The relative abundance of Citrobacter significantly decreased at the pupal and adult stages, while bacterial diversity increased. A mini literature survey revealed that members of the genus Citrobacter are associated with nitrogen fixation, recycling of uric acid nitrogen, and cellulose degradation in different insects. CONCLUSIONS The results suggest that although weevils could potentially acquire their gut bacteria from the soil, weevil host internal factors, rather than external environmental factors, were more important in shaping their gut bacterial communities, and suggest a major role for Citrobacter in weevil nutrition in this challenging environment. This study highlights the potential involvement of gut bacteria in the adaptation of insects to nutritional deficiencies under extreme desert conditions.

中文翻译：

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极端沙漠条件下，植物根部上会长出象鼻虫的肠道细菌。

背景技术许多食草昆虫通常饮食中的氮缺乏，它们依靠肠道细菌来补偿营养不足。因此，我们假设沙漠环境中的昆虫可能与肠道细菌发生进化，以适应极低的养分利用率。为此，我们基于16S rRNA基因扩增子序列，对附着在以色列内盖夫沙漠植物根部的泥室内部发育的象鼻虫肠道内的细菌群落进行了系统的调查。结果我们的分析表明，象鼻虫幼虫的肠道细菌群落在广泛的地理范围内相似，但与泥室和周围土壤的肠道细菌群落有显着差异。尽管如此，象鼻虫中也发现了很大比例的细菌（包括所有核心细菌），它们在泥室和土壤中以较低的相对丰度被检测到。柠檬酸杆菌属（肠杆菌科）是所有象鼻虫肠道中的主要菌群。在the期和成年期，柠檬酸杆菌的相对丰度显着降低，而细菌多样性则增加。一份小型文献调查显示，柠檬酸杆菌属的成员与固氮，尿酸氮的循环利用和纤维素在不同昆虫中的降解有关。结论结果表明，尽管象鼻虫有可能从土壤中获得肠道细菌，但象鼻虫是内部因素而不是外部环境因素，在塑造肠道细菌群落方面更为重要，并表明在这种挑战性环境中，柠檬酸杆菌在象鼻营养中起着重要作用。这项研究强调了肠道细菌可能在极端沙漠条件下使昆虫适应营养缺乏的潜在原因。