Salt-induced changes in lipid composition and membrane fluidity of halophilic yeast-like melanized fungi

Abstract

The halophilic melanized yeast-like fungi Hortaea werneckii, Phaeotheca triangularis, and the halotolerant Aureobasidium pullulans, isolated from salterns as their natural environment, were grown at different NaCl concentrations and their membrane lipid composition and fluidity were examined. Among sterols, besides ergosterol, which was the predominant one, 23 additional sterols were identified. Their total content did not change consistently or significantly in response to raised NaCl concentrations in studied melanized fungi. The major phospholipid classes were phosphatidylcholine and phosphatidylethanolamine, followed by anionic phospholipids. The most abundant fatty acids in phospholipids contained C16 and C18 chain lengths with a high percentage of C18:2Delta9,12. Salt stress caused an increase in the fatty acid unsaturation in the halophilic H. werneckii and halotolerant A. pullulans but a slight decrease in halophilic P. triangularis. All the halophilic fungi maintained their sterol-to-phospholipid ratio at a significantly lower level than did the salt-sensitive Saccharomyces cerevisiae and halotolerant A. pullulans. Electron paramagnetic resonance (EPR) spectroscopy measurements showed that the membranes of all halophilic fungi were more fluid than those of the halotolerant A. pullulans and salt-sensitive S. cerevisiae, which is in good agreement with the lipid composition observed in this study.

Osmotic adaptation of the halophilic fungus Hortaea werneckii: role of osmolytes and melanization

“…However, in H. werneckii the total sterol content remained largely unchanged with increased salinity, and the cells maintained high membrane fluidity over a broad range of salinities. Membrane fluidity was lower than in S. cerevisiae and in the halotolerant A. pullulans (Turk et al, 2004). Seemingly, there is a contradiction in the facts that (i) H. werneckii can grow at very high salinities, which require a high intracellular amount of glycerol, and (ii) at the same time it maintains a very fluid membrane by keeping a low sterolto-phospholipid ratio, which does not prevent glycerol leakage.…”

“…In the halophilic alga Dunaliella sp., the membrane permeability for glycerol is considerably lowered (Brown et al, 1982;Gimmler & Hartung, 1988), which is correlated with its high sterol content (Oren, 1999;Sheffer et al, 1986). In H. werneckii and other halophilic and halotolerant melanized fungi, ergosterol as the principal sterol and 23 other types of sterols (Turk et al, 2004) constitute the most distinctive lipid fraction of the cell membranes (Méjanelle et al, 2000). However, in H. werneckii the total sterol content remained largely unchanged with increased salinity, and the cells maintained high membrane fluidity over a broad range of salinities.…”

Properties of the halophyte microbiome and their implications for plant salt tolerance

“…Comparing different fungi revealed the composition of cell membranes as another adaptation to hypersalinity. In contrast to halosensitive Saccharomyces cerevisiae and some halotolerant filamentous fungi, Hortaea werneckii is able to maintain its sterol-to-phospholipid ratio at a constant level (Turk et al 2004). This is probably due to the expression of particular fatty acid-modifying enzymes upon salt stress (Gostincar et al 2009).…”

Epigallocatechin-3-gallate affects the growth of LNCaP cells via membrane fluidity and distribution of cellular zinc

“…However, it should be noted that changes in membrane fluidity need not necessarily render them 'leaky' since transport or translocation of compounds across cell membranes is a different physiological process, which is not directly related to the horizontal fluidity of the membrane. Changes in cell membrane fluidity depend to a large extent on the content of unsaturation of fatty acids in the phospholipid fraction of membranes (Thewke et al, 2000;Turk et al, 2004). It was noted that PC-3 cells treated with EGCG or Zn 2+ contained low levels of unsaturated fatty acids and showed a decrease in membrane fluidity.…”