Organismal interactions within microbial consortia and their responses to harmful intruders remain largely understudied. An important step toward the goal of understanding functional ecological interactions and their evolutionary selection is the study of increasingly complex microbial interaction systems. Here, we discovered a tripartite biosystem consisting of the fungus Aspergillus nidulans, the unicellular green alga Chlamydomonas reinhardtii, and the algicidal bacterium Streptomyces iranensis. Genetic analyses and MALDI-IMS demonstrate that the bacterium secretes the algicidal compound azalomycin F upon contact with C. reinhardtii. In co-culture, A. nidulans attracts the motile alga C. reinhardtii, which becomes embedded and surrounded by fungal mycelium and is shielded from the algicide. The filamentous fungus Sordaria macrospora was susceptible to azalomycin F and failed to protect C. reinhardtii despite chemotactically attracting the alga. Because S. macrospora was susceptible to azalomycin F, this data imply that for protection the fungus needs to be resistant. Formation of the lichen-like association between C. reinhardtii and A. nidulans increased algal growth. The protection depends on the increased amounts of membrane lipids provided by resistant fungi, thereby generating a protective shelter against the bacterial toxin. Our findings reveal a strategy whereby algae survive lethal environmental algicides through cooperation with fungi.

微生物群落内的有机相互作用及其对有害入侵者的反应在很大程度上仍未得到充分研究。朝着理解功能性生态相互作用及其进化选择的目标迈出的重要一步是研究日益复杂的微生物相互作用系统。在这里，我们发现了一个由真菌构巢曲霉、单细胞绿藻莱茵衣藻和杀藻细菌伊朗链霉菌组成的三重生物系统。遗传分析和 MALDI-IMS 表明，该细菌在与莱茵衣藻接触后会分泌杀藻化合物阿扎霉素 F。在共培养中，构巢构巢菌吸引能动的藻类莱茵藻，后者被真菌菌丝体嵌入并包围，并免受杀藻剂的影响。丝状真菌Sordaria macrospora对阿扎霉素 F 敏感，尽管能够趋化性地吸引藻类，但无法保护莱茵衣藻。由于大孢子菌对阿扎霉素 F 敏感，该数据意味着为了保护真菌需要具有抗性。莱茵衣藻和构巢曲霉之间类似地衣的结合的形成促进了藻类的生长。这种保护取决于抗性真菌提供的膜脂量的增加，从而产生针对细菌毒素的保护性庇护所。我们的研究结果揭示了藻类通过与真菌合作在致命的环境杀藻剂中生存的策略。