Antarctic Epilithic Lichens as Niches for Black Meristematic Fungi

Abstract

Sixteen epilithic lichen samples (13 species), collected from seven locations in Northern and Southern Victoria Land in Antarctica, were investigated for the presence of black fungi. Thirteen fungal strains isolated were studied by both morphological and molecular methods. Nuclear ribosomal 18S gene sequences were used together with the most similar published and unpublished sequences of fungi from other sources, to reconstruct an ML tree. Most of the studied fungi could be grouped together with described or still unnamed rock-inhabiting species in lichen dominated Antarctic cryptoendolithic communities. At the edge of life, epilithic lichens withdraw inside the airspaces of rocks to find conditions still compatible with life; this study provides evidence, for the first time, that the same microbes associated to epilithic thalli also have the same fate and chose endolithic life. These results support the concept of lichens being complex symbiotic systems, which offer attractive and sheltered habitats for other microbes.

The plasticity of fungal interactions

“…Although the nature of the relationships in lichens is still the subject of debate, it is widely accepted that it ranges from mutualism to controlled parasitism and changes dynamically over time (e.g., Ahmadjian and Jacobs 1981;Nash 1996;Richardson 1999). The definition of a lichen is further complicated by the presence of diverse, thallus-associated eukaryotic and prokaryotic entities (Zedda and Rambold 2015), including fungi (parasites, saprotrophs, and parasymbionts; Hawksworth 1982Hawksworth , 2015Lawrey and Diederich 2003;Selbmann et al 2013), non-symbiotic algae (diatoms; Lakatos et al 2004), terrestrial and aquatic invertebrates (arthropods, nematodes, Alveolata, Metazoa, Rhizaria; Bates et al 2012), protists (Šatkauskienė 2012), as well as bacterial communities (Bates et al 2011;Aschenbrenner et al 2016). Providing favorable conditions for other organisms, the lichen thallus appears to constitute an ecological niche (Hawksworth 1982) or even a miniature, intricate ecosystem (Aschenbrenner et al 2016), as already postulated in the 1970s (Farrar 1976).…”

Rock black fungi: excellence in the extremes, from the Antarctic to space

“…1) that may play a crucial role in photobionts protection by dangerous sunlight exposition (Selbmann et al 2013b).…”

“…Being heterotrophs, Antarctic RIF take advantage for nutrition from the spatial association with autotrophic, similarly stress-resistant organisms, and benefit from simple carbon sources such as glucose resulting from photosynthesis of neighboring algae and cyanobacteria (Selbmann et al 2013b). Yet, black fungi are extremely well adapted to rely on the few nutrients available: their metabolism and growth rates are extremely slow and cannot be increased even when cultured on rich media and optimal physical conditions.…”

“…They are also known as black yeasts or, when living on rocks, microcolonial fungi (MCF) or rock inhabitant fungi (RIF) (Sterflinger 1998;Ruibal et al 2009). In the cryptoendolithic communities of the Antarctic, they live in association with similarly stress-resistant organisms such as lichens (Onofri et al 2007a;Harutyunyan et al 2008;Selbmann et al 2013b) and cyanobacteria (de los Ríos et al 2014). More than 150 isolates are preserved in the Culture Collection of Fungi from Extreme Environments (CCFEE), Mycological section of the Italian National Museum for the Antarctic.…”

Distributional records of Antarctic fungi based on strains preserved in the Culture Collection of Fungi from Extreme Environments (CCFEE) Mycological Section associated with the Italian National Antarctic Museum (MNA)

“…Isolation from lichens was performed according to Selbmann et al (2013). Isolation from other sediments, soils, and mosses was performed by diluting 1g of each substrate in 1 l of sterile water and plating 100 µl of the suspension in a 9 cm Petri dish containing MA or Czapek dox agar (CZA).…”