Melanised rock-inhabiting fungi are astonishingly resistant to environmental stresses. Also known as micro-colonial fungi (MCF), they are ubiquitous and even colonise bare rocks in deserts. To survive in nutrient poor and extremely stressful conditions, MCF have reduced morphogenetic complexity to a minimum, and rely on a broad spectrum of stress protection mechanisms. Although visual signs of carotenoid presence are masked by heavily melanised black cell-walls, we were able to isolate and characterise a variety of carotenoids (ß-carotene, ζ-carotene, phytoene, torularhodin and torulene) in the rock-inhabiting, relatively fast-growing strain A95. The desiccation/rehydration stress response was used to measure the ability of A95 to adapt to slow or fast changes in external conditions. Revival of MCF after prolonged desiccation and rehydration was documented by biochemical (analyses of lipids and protective pigments), cultivation, and microscopic methods. Survival of MCF is enhanced when desiccation is rapid and mycostasis is instant rather than following prolonged periods of low metabolic activity.

The heat shock (HS) response is an adaptation of organisms to elevated temperature. It includes substantial changes in the composition of cellular membranes, proteins and soluble carbohydrates. To protect the cellular macromolecules, thermophilic organisms have evolved mechanisms of persistent thermotolerance. Many of those mechanisms are common for thermotolerance and the HS response. However, it remains unknown whether thermophilic species respond to HS by further elevating concentrations of protective components. We investigated the composition of the soluble cytosol carbohydrates and membrane lipids of the thermophilic fungi Rhizomucor tauricus and Myceliophthora thermophilaat optimum temperature conditions (41–43 °С), and under HS (51–53 °С). At optimum temperatures, the membrane lipid composition was characterized by a high proportion of phosphatidic acids (PA) (20–35 % of the total), which were the main components of the membrane lipids, together with phosphatidylcholines (PC), phosphatidylethanolamines (PE) and sterols (St). In response to HS, the proportion of PA and St increased, and the amount of PC and PE decreased. No decrease in the degree of fatty acid desaturation in the major phospholipids under HS was detected. The mycelium of all fungi at optimum temperatures contained high levels of trehalose (8–10 %, w/w; 60–95 % of the total carbohydrates), which is a hallmark of thermophilia. In contrast to mesophilic fungi, heat exposure decreased the trehalose level and the fungi did not acquire thermotolerance to lethal HS, indicating that trehalose plays a key role in this process. This pattern of changes appears to be conserved in the studied filamentous thermophilic fungi.

Comparison of the changes in the composition of the membrane lipids and soluble cytosol carbohydrates caused by two types of heat influence (within the tolerance zone and heat shock-level) revealed fundamental differences in the stress response of fungal cells. In three fungal species, Aspergillus niger, Pleurotus ostreatus, and Cunninghamella japonica, increased levels of trehalose and phosphatidic acids were observed under heat shock, while heat influences within the tolerance zone had no such effect. Under heat shock, the ratio of saturated fatty acids did not increase in any of the major phospholipids of all the studied species. This is in contradiction with the existing hypothesis and confirms the previously suggested the hypothesis of membrane stabilization by heat-protecting compounds.

Qualitative and quantitative characteristics of the alterations in the lipid composition of the membrane of the basidial fungus Flammulina velutipesin the course of surface culture development were...