Department of Molecular Microbiology, John Innes Centre, Norwich Research Park, Norwich, Norfolk, NR4 7UH, UK.
School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich, Norfolk, NR4 7TJ, UK.
Nat Commun. 2018 Jun 7;9(1):2208. doi: 10.1038/s41467-018-04520-1.
Acromyrmex leafcutter ants form a mutually beneficial symbiosis with the fungus Leucoagaricus gongylophorus and with Pseudonocardia bacteria. Both are vertically transmitted and actively maintained by the ants. The fungus garden is manured with freshly cut leaves and provides the sole food for the ant larvae, while Pseudonocardia cultures are reared on the ant-cuticle and make antifungal metabolites to help protect the cultivar against disease. If left unchecked, specialized parasitic Escovopsis fungi can overrun the fungus garden and lead to colony collapse. We report that Escovopsis upregulates the production of two specialized metabolites when it infects the cultivar. These compounds inhibit Pseudonocardia and one, shearinine D, also reduces worker behavioral defenses and is ultimately lethal when it accumulates in ant tissues. Our results are consistent with an active evolutionary arms race between Pseudonocardia and Escovopsis, which modifies both bacterial and behavioral defenses such that colony collapse is unavoidable once Escovopsis infections escalate.
切叶蚁与真菌 Leucoagaricus gongylophorus 和放线菌 Pseudonocardia 形成互利共生关系。这两种共生体都是垂直传播的，并由蚂蚁积极维持。菌圃用新鲜的切叶喂养，是蚁幼虫的唯一食物来源，而放线菌培养物则在蚁表皮上生长，并产生抗真菌代谢物，以帮助保护培养物免受疾病侵害。如果不加控制，专门的寄生 Escovopsis 真菌会过度繁殖菌圃，导致蚁群崩溃。我们报告称，Escovopsis 在感染菌圃时会上调两种特殊代谢物的产生。这些化合物抑制了 Pseudonocardia，其中一种名为 shearinine D 的化合物还降低了工蚁的行为防御能力，当它在蚂蚁组织中积累时，最终会导致致命后果。我们的研究结果与 Pseudonocardia 和 Escovopsis 之间的积极进化军备竞赛相一致，这种竞赛改变了细菌和行为防御，使得一旦 Escovopsis 感染升级，蚁群崩溃就不可避免。
