Lichenicolous fungi are fungi dwelling on or in lichens (Kirk et al. 2001). Today about 1000 species of obligate lichenicolous fungi are known. Most of them are visible to the naked eye on their host lichens (e.g. Phacopsis). However, a much wider range of fungi may be associated with lichens (Petrini et al. 1990, Girlanda et al. 1997, Caretta et al. 1998). They are mainly supposed to spread as sterile mycelia inside the lichens and are therefore not visible – mostly even not with optical devices. Therefore, we call them cryptic lichenicolous fungi.
The Letharietum vulpinae
The character species of the lichen community Letharietum vulpinae is Letharia vulpina, the wolf lichen. It grows on the bark of conifers (Central Europe, North Africa, North America) or on dead wood (Scandinavia, North America). Species of other fruticose (Bryoria, Evernia, Usnea) and foliose lichenised genera (Hypogymnia, Imshaugia, Melanelia, Parmeliopsis, Pseudevernia) accompany Letharia.
The sampling sites
Cryptic lichenicolous fungi were isolated from four sites in Europe and two in North America. Three of the former ones are located in the Alps at about 1900 m altitude: in the Nationalpark Berchtesgaden (Germany), at Turracher Höhe in Kärnten (Austria) and in Valle di Susa (Italy). The fourth European site is located in Sweden, near Sörvattnet. In California (USA), fungi were isolated in the James reserve (San Jacinto Mountains) and near the Sky Oaks field station.
Letharietum vulpinae on bark of Larix decidua
The sampling method (Peršoh 2002b)
The fungi were isolated in the field to reduce the number of possible contamination sources. The uppermost one mm of side branches of fruticose lichens - respectively a corresponding piece of the margin of foliose specimens - was transferred directly from the lichen (which was left attached to the tree) to the culture media, using sterile tweezers. Afterwards, the tweezers were used to drag the lichen fragment through the agar and tear it in smaller parts, which were spread over the whole plate. In the laboratory, the plates were examined regularly (daily within the first two weeks) and growing mycelia were transferred immediately to fresh media when detected. This way, from one lichen fragment up to 80 fungal strains could be isolated to pure culture.
Sampling site in the Nationalpark Berchtesgaden
The molecular analyses (Peršoh 2002b)
Most of the fungal strains do not sporolate under culture conditions. Therefore, we use molecular methods to classify the cryptic lichenicolous fungi. SSU and ITS nrDNA sequence data are gathered from the isolated strains. The SSU nrDNA sequences are aligned together with about 1000 fungal sequences obtained from GenBank. In most cases, phylogenetic analyses of the alignment make a classification of the fungi possible (e.g., assignment to a certain family). Analyses of the corresponding ITS nrDNA data allow us to further classify (e.g., assignment to a certain genus), or even identify the fungi.
The first results - fungi isolated from Usnea cf. subfloridana Stirt
First results were presented
at the IMC7 in Oslo (Peršoh 2002b). From Usnea cf. subfloridana
specimens at the three sampling sites in the European Alps 29 fungal
strains were isolated. They were assigned to the following taxonomic
groups by SSU nrDNA sequence analyses (numbers of isolates are given in
(mitosporic) Trichocomaceae (1)
The isolated Ascomycetes were
exclusively members of the Pezizomycotina. 19 of the 25 Pezizomycotina
could be assigned to five certain classes, two isolates formed a
sistergroup to a clade which included taxa of more than one class and
four clustered at the base the Chaetothyriomycetes clade. As a result
of the SSU nrDNA sequence analyses, the members of the Eurotiomycetes,
Lecanoromycetes and Sordariomycetes could be assigned to certain
families. The phylogenetic topology of the Dothideomycetes and
Leotiomycetes is not in accordance with the current taxonomy of the
groups and therefore most of these cultures these cannot be classified
An ITS nrDNA alignment,
constructed in the context of a study of the phylogeny
of the Xylariaceae, was used to identify one isolated fungus as Hypoxylon
fuscum (Pers.) Fr.. The Valsaceaen strains were identified as Leucostoma
curreyi (Nitschke) Défago. The two wood inhabiting species
were probably present in the form of spores on the lichen. The
Parmeliacean fungus belongs to the genus Usnea and is
presumably a culture of the primary mycobiont. Primarily, we estimate
interesting results from analyses of the ITS nrDNA alignments of the
Dothideomycetes and Leotiomycetes, since they comprise many obligate
lichenicolous fungi and the majority of the isolates.
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