Studies on the cultures of isolated symbionts of lichens and mixed cultures of both symbionts as new sources of bioactive compounds

地衣是共生生物体，由真菌（mycobiont）和光合作用伙伴（photobiont）组成。在某些情况下，培养的地衣菌生菌在逆境胁迫条件下具有产生新物质的能力。指出地衣真菌培养物可能成为生物活性物质的新来源。在我们对培养地衣菌群的研究过程中，我们培养了在日本收集的地衣菌群，并研究了它们的代谢产物。从黑纹草（Graphis proserpens）中分离得到三个新的异香豆素类化合物和三个新的萘并吡喃酮类化合物，其中沿着有六个已知化合物。从培养的Graphis connectans真菌中分离得到3个新化合物，并鉴定了它们的结构，其代谢产物的多样性是地衣化状态下从未发现过的。这一发现表明共生藻对真菌的次级代谢有一定的影响。我们研究了触发分离的菌生体和光生体再合成的条件。在琼脂培养基上共同培养的两种共生体的混合物中，真菌菌落与藻层的表面接触，但两种真菌都没有穿透藻细胞。另一方面，在液体培养基中观察到真菌与藻类之间的附着，并且在混合物的中心，分支的真菌菌丝经常穿透藻类细胞。在某些实验中，藻类和真菌的结合不同于天然地衣，这种不匹配可能解释寄生而不是共生的发生。进一步的研究，以阐明的因素，诱导重新合成的两个组件可以提供重要的信息，共生地衣和良好的工具，生产有用的次级产品。

Lichens are symbiotic organisms comprised of a fungus, mycobiont, and a photosynthetic partner, photobiont. In some cases, cultures of lichen mycobionts have an ability under osmotically stressed conditions to produce new substances. It was pointed out that cultures of lichen mycobionts could be new sources of bioactive compounds. In the course of our studies on cultured lichen mycobionts, we cultivated mycobionts of the lichens collected in Japan and investigated their metabolites. From the cultures of Graphis proserpens, three new isocoumarins and three novel compounds derived from naphthopyrones through an oxidative ring cleavage were isolated along with six known compounds. From the cultured mycobionts of Graphis connectans, three new compounds were obtained and their structures were also elucidated.The diverse metabolites of the cultured mycobionts have never been found in the lichenized state. The finding suggested that the secondary metabolism of mycobionts could be influenced by the algal partner in symbiosis. We investigated the conditions which trigger re-synthesis of the isolated mycobiont and photobiont. In the mixture of both symbionts cultured together on agar medium, mycobiont colonies were in contact with the surface of the algal layer, but neither mycobiont species penetrated the algal cells. On the other hand, the attachment between the mycobiont and algae in the liquid medium was observed and in the center of the mixture, branched mycobiont hyphae often penetrated algal cells. The combination between algae and mycobionts in some experiments was different from the natural lichens and this mismatch may explain the occurrence of parasitism instead of symbiosis. Further studies to elucidate the factors which induce the re-synthesis of the two components could give important information about the symbiosis of lichens and good tools for the production of useful secondary products.