The beauty and the yeast: can the microalgaeDunaliellaform a borderline lichen withHortaea werneckii?

Muggia, L., Zalar, P., Azua Bustos, A., González Silva, C., Grube, M., Gunde Cimerman, N. (2020). The beauty and the yeast: can the microalgaeDunaliellaform a borderline lichen withHortaea werneckii?. Symbiosis DOI: 10.1007/s13199-020-00697-6

Lichenized fungi usually develop complex, stratified morphologies through an intricately balanced living together with their algal partners, but several species are known to form only more or less loose associations with algae. These borderline lichens are still little explored although they could inform us about early stages of lichen evolution. We studied the association of the extremely halotolerant fungusHortaea werneckiiwith the algaDunaliella atacamensis, discovered in a cave in the Atacama Desert (Chile), and withD. salina, common inhabitant of saltern brines.D. atacamensisforms small colonies, in which cells ofH. werneckiican be frequently observed, while such interaction has not been observed withD. salina. As symbiotic interactions betweenDunaliellaandHortaeahave not been reported, we performed a series of co-cultivation experiments to inspect whether these species could interact and develop more distinct lichen-like symbiotic structures. We set up co-cultures between axenic strains ofHortaea werneckii(isolated both from Mediterranean salterns and from the Atacama cave) and isolates ofD. atacamensis(from the Atacama cave) andD. salina(isolated from Mediterranean salterns). Although we used different growth media and cultivation approaches, bright field and SEM microscopy analyses did not indicate any mutual effects in these experiments. We discuss the implications for fungal algal interactions along the transition from algal exploiters to lichen symbioses.

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