Heat shock response of thermophilic fungi: membrane lipids and soluble carbohydrates under elevated temperatures

Abstract

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.

Soluble Sugar and Lipid Readjustments in the Yarrowia lipolytica Yeast at Various Temperatures and pH

“…As far as minor membrane lipids, there was also some increase in the PA fraction in the membrane lipids under both thermal and combined stresses. The data are agree well with the results obtained by [60], where the authors using the Aspergilus niger fungus showed that various stressful factors (heat and cold shock, oxidative and osmotic stress) led to a significant increase in the PA level in the membranes. They speculated that the PAs contributed to the fungus adaptive defense responses to stress by increasing the cell membrane stability and by intensifying vesicular transport, and endo-and exocytosis.…”

Metabolic engineering of the cellulolytic thermophilic fungus Myceliophthora thermophila to produce ethanol from cellobiose

“…During heat shock, Hsp104 contributes to the simultaneous increase in both the accumulation and degradation of trehalose in S. cerevisiae [50]. Trehalose plays a vital role in the heat shock response of S. cerevisiae and M. thermophila [51,52]. Consistent with the downregulation of Mycth_80427 (hsp104), genes involved in trehalose biosynthesis (Mycth_2082262, Mycth_2295490, Mycth_2309547) were also downregulated in JY518 compared with WT grown with cellobiose as the carbon source ( Fig.…”

Membrane lipid and osmolyte readjustment in the alkaliphilic micromycete Sodiomyces tronii under cold, heat and osmotic shocks

“…Analyses of lipids, carbohydrates and polyols were performed as described previously [25]. Briefly, lipids were extracted by the Nichols method [26] with phospholipase-deactivating isopropanol, separated by two-dimensional (polar lipids) or one-dimensional (neutral lipids) TLC [27] and quantified using standard compounds with a densitometry method (DENS software).…”