Key Laboratory of Insect Developmental and Evolutionary Biology, CAS Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences, Shanghai, 200032, China.
School of Life Science and Technology, ShanghaiTech University, Shanghai, 201210, China.
Microbiome. 2024 Feb 26;12(1):40. doi: 10.1186/s40168-024-01764-6.
Bacterial transfers from plants to insect herbivore guts have been well investigated. However, bacterial exchanges between plant phyllospheres and insect cuticles remain unclear, as does their related biological function.
Here, we report that the cuticular bacterial loads of silkworm larvae quickly increased after molting and feeding on the white mulberry (Morus alba) leaves. The isolation and examination of silkworm cuticular bacteria identified one bacterium Mammaliicoccus sciuri that could completely inhibit the spore germination of fungal entomopathogens Metarhizium robertsii and Beauveria bassiana. Interestingly, Ma. sciuri was evident originally from mulberry leaves, which could produce a secreted chitinolytic lysozyme (termed Msp1) to damage fungal cell walls. In consistency, the deletion of Msp1 substantially impaired bacterial antifungal activity. Pretreating silkworm larvae with Ma. sciuri cells followed by fungal topical infections revealed that this bacterium could help defend silkworms against fungal infections. Unsurprisingly, the protective efficacy of ΔMsp1 was considerably reduced when compared with that of wild-type bacterium. Administration of bacterium-treated diets had no negative effect on silkworm development; instead, bacterial supplementation could protect the artificial diet from Aspergillus contamination.
The results of this study evidence that the cross-kingdom transfer of bacteria from plant phyllospheres to insect herbivore cuticles can help protect insects against fungal parasite attacks. Video Abstract.
植物向昆虫食草动物肠道转移的细菌已得到充分研究。然而，植物叶际与昆虫表皮之间的细菌交换及其相关生物学功能仍不清楚。
我们报告称，家蚕幼虫在蜕皮后取食白桑（Morus alba）叶片，其表皮细菌负荷迅速增加。对家蚕表皮细菌的分离和检查鉴定出一种细菌 Mammaliicoccus sciuri，它可以完全抑制真菌昆虫病原物玫烟色棒束孢（Metarhizium robertsii）和球孢白僵菌（Beauveria bassiana）的孢子萌发。有趣的是，Ma. sciuri 最初来源于桑叶，它可以产生一种分泌的几丁质溶解酶（称为 Msp1）来破坏真菌细胞壁。同样，Msp1 的缺失大大削弱了细菌的抗真菌活性。用 Ma. sciuri 细胞预处理家蚕幼虫，然后进行真菌局部感染，结果表明该细菌可以帮助家蚕抵御真菌感染。不出所料，与野生型细菌相比，ΔMsp1 的保护效果显著降低。给予细菌处理的饮食对家蚕的发育没有负面影响；相反，细菌补充可以保护人工饮食免受曲霉菌的污染。
本研究结果表明，细菌从植物叶际向昆虫食草动物表皮的跨界转移可以帮助昆虫抵御真菌寄生虫的攻击。视频摘要。
