Hounsa Charlemagne-Gilles, Brandt E Vincent, Thevelein Johan, Hohmann Stefan, Prior Bernard A
Department of Microbiology and Biochemistry.
Department of Chemistry, University of the Orange Free State, Bloemfontein 9300, South Africa.
Microbiology (Reading). 1998 Mar;144 ( Pt 3):671-680. doi: 10.1099/00221287-144-3-671.
Trehalose is an enigmatic compound that accumulates in Saccharomyces cerevisiae and has been implicated in survival under various stress conditions by acting as membrane protectant, as a supplementary compatible solute or as a reserve carbohydrate that may be mobilized during stress. In this study, specific mutants in trehalose metabolism were used to evaluate whether trehalose contributes to survival under severe osmotic stress and generates the compatible solute glycerol under moderate osmotic stress. The survival under severe osmotic stress (0.866 aw' NaCl or sorbitol) of mutants was compared to that of the wild-type strain when cultivated to either the mid-exponential or the stationary growth phase on glucose, galactose or ethanol. Stationary-phase cells survived better than exponential-phase cells. The death rates of ethanol-grown cells were lower than those of galactose-grown cells, which in turn survived better than glucose-grown cells. There was a strong relationship between intracellular trehalose levels and resistance to osmotic stress. The mutant strains unable to produce trehalose (tps1 delta tps2 delta and tps1 delta hxk2 delta) were more sensitive to severe osmotic stress (0.866 aw) than the isogenic wild-type strain, confirming a role for trehalose in survival. Hyperaccumulation of trehalose found in the nth1 delta and the nth1 delta gpd1 delta mutant strains, however, did not improve survival rates compared to the wild-type strain. When wild-type, nth1 delta and nth1 delta gpd1 delta cells were exposed to moderate osmotic stress (0.98 and 0.97 aw' NaCl), which permits growth, glycerol production did not appear to be related to the intracellular trehalose levels although glycerol levels increased more rapidly in nth1 delta cells than in wild-type cells during the initial response to osmotic stress. These data indicate that trehalose does not act as a reserve compound for glycerol synthesis under these conditions. No evidence was found for solutes other than glycerol and trehalose being significant for the survival of or growth by S. cerevisiae under osmotic stress conditions.
海藻糖是一种神秘的化合物，它在酿酒酵母中积累，并通过充当膜保护剂、补充性相容性溶质或在应激期间可能被动员的储备碳水化合物，在各种应激条件下参与细胞存活过程。在本研究中，利用海藻糖代谢的特定突变体来评估海藻糖是否有助于在严重渗透胁迫下存活，以及在中等渗透胁迫下是否产生相容性溶质甘油。将突变体在葡萄糖、半乳糖或乙醇上培养至指数中期或稳定生长期后，比较其在严重渗透胁迫（0.866 aw的NaCl或山梨醇）下与野生型菌株的存活率。稳定期细胞比指数期细胞存活得更好。乙醇培养的细胞死亡率低于半乳糖培养的细胞，而半乳糖培养的细胞又比葡萄糖培养的细胞存活得更好。细胞内海藻糖水平与对渗透胁迫的抗性之间存在很强的相关性。无法产生海藻糖的突变菌株（tps1Δtps2Δ和tps1Δhxk2Δ）比同基因野生型菌株对严重渗透胁迫（0.866 aw）更敏感，这证实了海藻糖在存活中的作用。然而，与野生型菌株相比，在nth1Δ和nth1Δgpd1Δ突变菌株中发现的海藻糖过度积累并未提高存活率。当野生型、nth1Δ和nth1Δgpd1Δ细胞暴露于允许生长的中等渗透胁迫（0.98和0.97 aw的NaCl）时，甘油的产生似乎与细胞内海藻糖水平无关，尽管在对渗透胁迫的初始反应期间，nth1Δ细胞中的甘油水平比野生型细胞增加得更快。这些数据表明，在这些条件下，海藻糖不作为甘油合成的储备化合物。没有发现除甘油和海藻糖以外的溶质对酿酒酵母在渗透胁迫条件下的存活或生长有显著影响的证据。
