Compatible Solutes Protect against Chaotrope(Ethanol)-Induced, Nonosmotic WaterStress

Abstract

Water stress is one of the major stresses experienced by cellular systems and can take a number of distinct forms. In response to turgor-related osmotic stress, cells produce compatible solutes that are macromolecule protectants and also counteract the outflow of water from stressed cells. In this report we show that the germination of conidia of Aspergillus nidulans, a sensitive indicator of water stress, in the presence of ethanol is correlated with the intracellular concentration of the compatible solutes glycerol and erythritol, which protect against both osmotic and nonturgor forms of water stress.Cellular systems consist of up to 97% water, so thermodynamic changes in water availability cause fundamental biological stress that can severely impact vital metabolic processes (3). Water stress can be induced by a net loss of water from cells, e.g., due to high levels of extracellular solutes such as NaCl that reduce cell turgor and induce osmotic stress. Cells exposed to such agents are subjected to both reduced turgor and stabilizing effects on macromolecules, which can lead to membrane rigidity and impairment of protein structure (3,16,19,25). Intracellular water activity also may be reduced by chaotropic compounds, such as ethanol, that decrease the strength of hydrogen bonding and other electrostatic interactions and thereby perturb the structure and function of hydrated macromolecules, including nucleic acids, proteins, and lipids.Cells generally respond to osmotic stress by acquiring and/or producing compatible solutes that protect macromolecule structure and at the same time increase the osmotic pressure of the cytoplasm and thereby counteract water loss from cells (1, 3). Our working hypothesis is that these compatible solutes also protect against intracellular water stress due to alterations in the hydration of cellular macromolecules caused by ethanol, a chaotropic solute that does not cause osmotic stress.The ascomycete Aspergillus (Emericella) nidulans is a model microorganism whose genetics and metabolism, including those related to stress and toxicology, have been widely studied. A. nidulans, like most yeast and fungal cells, synthesizes low-molecular-weight polyols, such as glycerol, in response to osmotic stress (3, 21). Our objective in this study was to determine whether increased intracellular levels of glycerol and erythritol affect conidial germination in A. nidulans when the organism is cultured under conditions that reduce cell turgor and induce osmotic stress (e.g., in a high-NaCl environment), as well as those that increase intracellular water stress by reducing the strength of water-macromolecule interactions (e.g., at high ethanol concentrations). MATERIALS AND METHODSOrganism, media, and production of conidia. A culture of A. nidulans (IFO 4342) was obtained from the Institute for Fermentation Osaka (Osaka, Japan) and maintained on potato dextrose agar (PDA; Nissui, Tokyo, Japan) at 25°C. All media were buffered with 21.3 g of 2-(N-morpholino)ethanesulfonic acid (MES) liter Ϫ1 , and...

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“…It has been reported that mannitol is implicated in the stress response to heat [39] and that it is the most abundant polyol in conidia of A. nidulans [40]. One of the pathways that lead to mannitol proceeds via mannitol 1-phosphate, from the glycolytic intermediate fructose 6-phosphate, and another one, which has fructose as an intermediate.…”

A New Analysis of Mars “Special Regions”: Findings of the Second MEPAG Special Regions Science Analysis Group (SR-SAG2)

“…Chaotropes such as MgCl 2 , CaCl 2 , FeCl 3 , FeCl 2 , FeCl, LiCl, perchlorate, and perchlorate salts (Cray et al, 2013b) are, collectively, abundant in the regolith of Mars. The net chaotropicity of mixed-salt solutions (or, indeed, mixed solutions of other solute types) is influenced by the presence of stabilizing (kosmotropic) solutes, which are more polar than water (Oren, 1983;Hallsworth et al, 2003bHallsworth et al, , 2007Williams and Hallsworth, 2009;Bhaganna et al, 2010;Bell et al, 2013). It is nevertheless intriguing to speculate whether chaotropic salts on Mars might potentially expand the window for cell division of a microbial psychrophile by reducing the temperature minimum for metabolic activity.…”

Chaotropicity: a key factor in product tolerance of biofuel-producing microorganisms

“…[3 , 23,49 ]). Many compatible solutes including trehalose, proline, glycine betaine and mannitol are kosmotropic [7 ].…”

“…However, compatible-solute production and retention can be energy-expensive for the microbial cell. Studies of Aspergillus species provide further evidence for roles of glycerol and other polyols in ethanol tolerance [23,49 ]. Furthermore, carbon substrate that is utilized for trehalose or glycerol production may reduce potential ethanol yield.…”