BIOLOGY OF LICHENS

Univ. Doz. Dr. Elfriede Stocker

(Elfie Stocker-Wörgötter)

"Elfie"

Department of Organismic Biology

(former Institute for Plant Physiology)

University of Salzburg 

Hellbrunner Str. 34

A-5020 Salzburg, Austria

Europe

Tel. +43-662-8044-5509

Fax +43-662-8044-142 (office)

e-mail: elfriede.stocker@sbg.ac.at

Subculture, dark mycobiont

S4%-sucrose medium, 14 weeks.

Neuropogon antarcticus (Du Rietz) IM Lamb.

Subculture, bright mycobiont,

S2%-sucrose medium, 14 weeks.

Lichens are fascinating symbiotic associations, actually they represent a biological partnership of at least two different organisms. They have been defined as a stable and self-supporting symbiosis between fungi (the mycobionts) and photoautotrophic algal partners (the photobionts). More than 42% of ascomycetes and a few basidiomycetes (one fifth of all fungi) are involved in an extremely successful form of nutritional strategy and dependency. For this reason, lichens grow under diverse ecological conditions; they occur from arctic habitats to tropical rainforests where they colonize a broad variety of substrates, such as rock, bark, soil and even leaf surfaces. 

Most phylogenetic studies of lichen fungi have been performed on genes of the ribosomal DNA-cluster. Recently, phylogeny reconstructions of lichens include more and more protein-coding genes. Together with improvements of molecular techniques and approaches the lichen photobionts receive further attention. 

Lichens and lichen fungi have been recognized as a rich source of secondary metabolites since the beginning of the 20th century. However, the application of biologically active lichen substances has remained relatively unexplored until recent times. 

Large scale culture experiments have shown that selected mycobionts can be grown in optimized nutrient media in substantial amounts. Under simulated microclimatic changes and artificial stress situations in a culture chamber, many aposymbiotically grown fungi form highly differentiated and layered mycelia. Such fungal structures are found to produce the same or related secondary phenolic compounds typical for the corresponding lichen voucher specimens. Even complete chemosyndromes (a cohort of biosynthetically related metabolites) are occasionally formed in culture.

Recently, genetic approaches using PCR, genomic library construction and heterologous expression have been started to explore the diversity of polyketide biosynthetic pathways in lichens.