ALBERT

Description: INTRODUCTION: Lichens are self-sustaining partnerships comprising fungi as shape-forming partners for their enclosed symbiotic algae. They produce a tremendous diversity of metabolites (1050 metabolites described so far). OBJECTIVES: A comparison of metabolic profiles in nine lichen species belonging to three genera (Lichina, Collema and Roccella) by using an optimised extraction protocol, determination of the fragmentation pathway and the in situ localisation for major compounds in Roccella species. METHODS: Chemical analysis was performed using a complementary study combining a Taguchi experimental design with qualitative analysis by high-performance liquid chromatography coupled with mass spectrometry techniques. RESULTS: Optimal conditions to obtain the best total extraction yield were determined as follows: mortar grinding to a fine powder, two successive extractions, solid:liquid ratio (2:60) and 700 rpm stirring. Qualitative analysis of the metabolite profiling of these nine species extracted with the optimised method was corroborated using MS and MS/MS approaches. Nine main compounds were identified: 1 β-orcinol, 2 orsellinic acid, 3 putative choline sulphate, 4 roccellic acid, 5 montagnetol, 6 lecanoric acid, 7 erythrin, 8 lepraric acid and 9 acetylportentol, and several other compounds were reported. Identification was performed using the m/z ratio, fragmentation pathway and/or after isolation by NMR analysis. The variation of the metabolite profile in differently organised parts of two Roccella species suggests a specific role of major compounds in developmental stages of this symbiotic association. CONCLUSION: Metabolic profiles represent specific chemical species and depend on the extraction conditions, the kind of the photobiont partner and the in situ localisation of major compounds.

Description: A chemical study of the lichen Ramalina siliquosa complex found in Brittany was conducted. Eight chemotypes were considered and their chemical composition was elucidated for the first time by LC–MS analysis. Ten main compounds were identified: conhypoprotocetraric acid (1), salazinic acid (2), peristictic acid (3), cryptostictic acid (4), protocetraric acid (5), stictic acid (6), norstictic acid (7), hypoprotocetraric acid (8), 4-O-demethylbarbatic acid (9), (+)-usnic acid (10) and 22 minor compounds were reported. The MS/MS fragmentation patterns of each compound of R. siliquosa complex were determined and proposed.

Description: Lichens are among the most conspicuous and ubiquitous symbiosis on this planet. They are highly adapted to terrestrial habitats of all climatic zones including the most hostile environments on Earth, such as high altitudes in the Himalayas or the cold deserts of Antarctica. Among the extreme habitats are the littoral (or intertidal) zones of coasts. In this chapter, we present an overview of the current knowledge about the halotolerance mechanisms in lichens. Halotolerant organisms generally accumulate osmotically active solutes to cope with increasing external salinity. In intertidal lichens, mannitol could play an important role in osmoregulation. Epilichenic bacterial colonies may be also involved in limiting lichen nutrient imbalance by producing osmoprotective compounds and storing high ionic concentrations. In addition, the comparison with related inland species suggests that morphological adaptations could also be involved in adaptation to increased salt levels. Maritime species often have strongly conglutinated hyphae and small or no intercellular spaces in their thalli. So far, little genetic information exists about the genes involved in halotolerance and their regulation. Comparison of forthcoming genomic information from lichen fungi with those of other halotolerant fungi will soon help to change the picture and reveal genetic adaptations to saline environments.