Evolutionary Ecology, Institute of Organismic and Molecular Evolution (iomE), Johannes Gutenberg University, Mainz, Germany.
Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan.
Commun Biol. 2021 May 11;4(1):554. doi: 10.1038/s42003-021-02057-6.
Glyphosate is widely used as a herbicide, but recent studies begin to reveal its detrimental side effects on animals by targeting the shikimate pathway of associated gut microorganisms. However, its impact on nutritional endosymbionts in insects remains poorly understood. Here, we sequenced the tiny, shikimate pathway encoding symbiont genome of the sawtoothed grain beetle Oryzaephilus surinamensis. Decreased titers of the aromatic amino acid tyrosine in symbiont-depleted beetles underscore the symbionts' ability to synthesize prephenate as the precursor for host tyrosine synthesis and its importance for cuticle sclerotization and melanization. Glyphosate exposure inhibited symbiont establishment during host development and abolished the mutualistic benefit on cuticle synthesis in adults, which could be partially rescued by dietary tyrosine supplementation. Furthermore, phylogenetic analyses indicate that the shikimate pathways of many nutritional endosymbionts likewise contain a glyphosate sensitive 5-enolpyruvylshikimate-3-phosphate synthase. These findings highlight the importance of symbiont-mediated tyrosine supplementation for cuticle biosynthesis in insects, but also paint an alarming scenario regarding the use of glyphosate in light of recent declines in insect populations.
草甘膦被广泛用作除草剂，但最近的研究开始通过靶向相关肠道微生物的莽草酸途径揭示其对动物的有害副作用。然而，它对昆虫营养共生体的影响仍知之甚少。在这里，我们对锯齿谷盗（Oryzaephilus surinamensis）的微小、编码莽草酸途径的共生体基因组进行了测序。共生体耗竭的甲虫中天冬氨酸的含量降低，这突显了共生体合成预苯酸作为宿主酪氨酸合成前体的能力，以及其对表皮硬化和黑化的重要性。草甘膦暴露抑制了宿主发育过程中共生体的建立，并取消了共生体对成虫表皮合成的互利作用，而膳食酪氨酸补充可以部分挽救这种作用。此外，系统发育分析表明，许多营养共生体的莽草酸途径同样含有草甘膦敏感的 5-烯醇丙酮酰莽草酸-3-磷酸合酶。这些发现强调了共生体介导的酪氨酸补充对昆虫表皮生物合成的重要性，但也描绘了一个令人担忧的情景，即考虑到最近昆虫数量的下降，草甘膦的使用。
