Antifungal activity of lichen compounds against dermatophytes: a review

The growth rate inhibition of dermatophytes by compounds extracted by acetone, ethanol, methanol and water derived from representatives of several lichen genera (e.g. Caloplaca, Everniastrum, Heterodermia, Hypotrachyna, Platismatia and Ramalina) were compared on the basis of a worldwide review of published research. The examined dermatophytes included Epidermophyton floccosum, Microsporum audouinii, M. canis, M. gypseum, M. nanum, Trichophyton longifusus, T. mentagrophytes, T. rubrum, T. tonsurans and T. violaceum. The influence of selected secondary lichen compounds, for example, usnic acid, on the growth rates of these dermatophytes was also reviewed. The measurement of inhibition by lichen compounds was performed by several methods, but mostly those employing disc diffusion, broth dilution and agar dilution. The fungicidal activity of water-extracted compounds from Heterodermia leucomela and Hypotrachyna cirrhata and of methanol-extracted compounds from Evernia divaricata and Ramalina pollinaria, as well as protolichesterinic and 2-hydroxy-4-methoxy-3,6-dimethylbenzoic acids, are distinguished.     

A biological basis for lichenometry?

Aim Develop a biologically defensible conceptual model to explain lichen population dynamics. Methods This work critically examines the biological basis for several of the key assumptions that are used to interpret lichen-size age data. It then presents a biologically defensible conceptual model that can be used to develop computer based simulations of lichen population dynamics or to design alternative approaches to lichenometry. Main conclusions Most lichenometric ages are not verifiably accurate and are generated by methodologies that do not incorporate widely accepted biological principles. Polymodality in thallus-size distributions is not always the product of discrete events. Polymodality could reflect continuous changes in the availability of inhabitable patches (gaps) in a heterogenous mosaic. Improvement in lichenometry could be realized by investigations that seek to quantify the temporal and perhaps density-dependent onset of departures from statistical normality for certain lichen cohorts or species groupings. The study of lichen communities on substrates of known age may, in the short term provide some indication of the relative timing of age-stage changes in lichen demographic structure.     

Genetic and environmental effects of growth and production of secondary compounds in Cladonia cristatella

This is the first study under controlled conditions to evaluate genetic and environmental variables acting on the whole lichen. Four cloned lines of Cladonia cristatella, derived from single spores and re-associated with teh normal algal partner (Trebouxia erici), were grown in a phytotron and chemically analysed. Growth, as measured by cover, was significantly affected by clone and consistently decreased at lower temperatures and at higher light intensities. The two biogenetically distinct pathways leading to the characteristic secondary products were affected differently by factors related to the genetic component (clone), the developmental stage (age) and the environment (temperature and light). Products fo the barbatic acid pathway, leading to depsides, were detected in the youngest lichenized hyphae, and the concentrations did not change significantly with age. products of the didymic acid pathway, leading to dibenzofurans, were incrasingly abundant in progressively older squamules. The four clones showed significantly different capacities for the production of compounds by the two pathways and significantly different responses to the environmental factors studied. The concentrations of compounds from the barbatic acid pathway increased at lower temperatures; those of compounds from the didymic acid pathway either changed little or decreased appreciably according to clone. Of the factors studied, light had the least effect on chemistry. Between-pathway variation in production of secondary products was greater than within-pathway variation.