This study was intended to determine the osmoadaptation strategy of Hortaea werneckii, an extremely salt-tolerant melanized ascomycetous fungus that can grow at 0-5.1 M NaCl. It has been shown previously that glycerol is the major compatible solute in actively growing H. werneckii. This study showed that the exponentially growing cells also contained erythritol, arabitol and mannitol at optimal growth salinities, but only glycerol and erythritol at maximal salinities. The latter two were both demonstrated to be major compatible solutes in H. werneckii, as their decrease correlated with the severity of hypoosmotic shock. Besides higher amounts of erythritol and lower amounts of glycerol, stationary-phase cells also contained mycosporineglutaminol-glucoside, which might act as a complementary compatible solute. H. werneckii is constitutively melanized under various salinity conditions. Ultrastructural study showed localization of melanin in the outer parts of the cell wall as a distinct layer at optimal salinity (0.86 M NaCl), whereas cell-wall melanization diminished at higher salinities. The role of melanized cell wall in the effective retention of glycerol is already known, and was also demonstrated in H. werneckii by lower retention of glycerol in cells with blocked melanization compared to melanized cells. However, these non-melanized cells compensated for the lower amounts of glycerol with higher amounts of erythritol and arabitol. We hypothesize that H. werneckii melanization is effective in reducing the permeability of its cell wall to its major compatible solute glycerol, which might be one of the features that helps it tolerate a wider range of salt concentrations than most organisms.

A universal method allowing simultaneous extraction and analysis of diverse ultraviolet-B-absorbing compounds belonging to mycosporines and mycosporine-like amino acids (MAAs) is presented. Mycosporines and MAAs are found both in prokaryotes and eukaryotes and possess photoprotective properties. Our method was successfully tested by screening 31 cyanobacterial, 11 actinomycete and 45 fungal strains for their mycosporine and MAA content. The majority of the isolates tested originated from subaerial rock surfaces and were inherently protected from excessive sun irradiation. The new method includes a solid-liquid extraction procedure, followed by a reversed phase liquid chromatography/mass spectrometry. Eight different mycosporines and five MAAs were efficiently separated and identified by their retention times, absorption maxima and fragmentation patterns. Mycosporines were found both in rock-inhabiting fungi and cyanobacteria and consequently may render an ecological marker of these peculiar terrestrial environments.

Environmental Context.The occurrence of fungi in extreme environments, particularly in hypersaline water and in subglacial ice, is much higher than was previously assumed. When glacial ice melts as a result of calving or surface ablations, these organisms are released in the Arctic soil or sea and have a yet uninvestigated impact on the environment. Knowledge of the metabolites of these extremophilic fungi is important because they could provide signature molecules in the environment, but they can also contribute nutrients to the otherwise oligotrophic polar conditions. In the present work, we examine the osmotic behaviour of fungi grown under hypersaline conditions. Abstract.Fungi isolated from hypersaline waters and polar glacial ice were screened for the presence of mycosporines and mycosporine-like amino acids under non-saline and saline growth conditions. Two different mycosporines and three unidentified UV-absorbing compounds were detected by high performance liquid chromatography in fungal isolates from hypersaline waters and polar glacial ice. It was shown for the first time that the mycosporine–glutaminol–glucoside in halophilic and halotolerant black yeasts from salterns was higher on saline growth medium. This substance might act as a supplementary compatible solute in some extremophilic black yeasts exposed to saline growth conditions.

Life and its former traces can only be detected from space when they are abundant and exposed to the planetary atmosphere at the moment of investigation by orbiters. Exposed rock surfaces present a multifractal labyrinth of niches for microbial life. Based upon our studies of highly stress-resistant microcolonial fungi of stone monument and desert rock surfaces, we propose that microbial biofilms that develop and become preserved on rock surfaces can be identified remotely by the following characteristics: (1) the existence of spectroscopically identifiable compounds that display unique adsorption, diffraction, and reflection patterns characteristic of biogenerated organic compounds (e.g., chlorophylls, carotenes, melanins, and possibly mycosporines), (2) demonstrably biogenic geomorphological features (e.g., biopitting, biochipping, and bioexfoliation), and (3) biominerals produced in association with biofilms that occupy rock surfaces (e.g., oxalates, forsterite, and special types of carbonates, sulfides, and silicates). Such traces or biosignatures of former life could provide macroscopically visible morphotypes and chemically identifiable products uniquely indicative of life.

The unicellular cyanobacterium Euhalothece sp. strain LK-1, isolated from a gypsum crust on the bottom of a hypersaline saltern pond in Eilat, Israel, contains high concentrations of two mycosporine-like amino acids with maximum absorbance at 331 and 362 nm when grown at high light intensities. The 331 nm-absorbing compound has previously been identified as mycosporine-2-glycine. Here, we confirm this identification and document the elucidation of the structure of the 362 nm absorbing compound ('euhalothece-362'), using liquid chromatography/mass spectrometry combined with other techniques, as a novel compound, 2-(E)-3-(E)-2,3-dihydroxyprop-1-enylimino-mycosporine-alanine.