Yeasts salt-tolerant

Mulet JM, Leube MP, Kron SJ, Rios G, Fink GR, Serrano R (1999) A novel mechanism of ion homeostasis and salt tolerance in yeast the Hal4 and Hal5 protein kinases modulate the Trkl-Trk2 potassium transporter. Mol Cell Biol 19 3328-3337... 

Tag K, Lehmann M, Chan C, Renneberg R, Riedel K, Kunze G (2000) Measurement of biodegradable substances with a mycelia-sensor based on the salt tolerant yeast Arxula adeninivorans LS3. Sensors Actuators B67 142-148... 

Almagro, A., Prista, C., Benito, B., Loureiro-Dias, M. C. Ramos, J. (2001). Cloning and expression of two genes coding for sodium pumps in the salt tolerant yeast Debaryomyces hansenii. Journal of Bacteriology, 183, 3251-5. 

Nilsson, A. Adler, L. (1990). Purification and characterisation of glycerol-3-phosphate dehydrogenase (NAD+) in the salt tolerant yeast Debaryomyces hansenii. Biochimica et Biophysica Acta, 1034, 180-185. 

Quintero, F.J., Garciadeblas, B., and Rodriguez-Navarro, A., 1996, The Sail gene of Arabidopsis, encoding an enzyme with 3,(2,),5,(-bisphosphate nucleotidase and inositol polyphosphatase 1-phosphatase activities, increases salt tolerance in yeast. Plant Cell 8 529-537. 

The more acetaldehyde is trapped by the sodium sulfite, the greater is the quantity of glycerol found, but the yeast can tolerate only a certain percentage of this salt before it exerts a toxic effect. Sodium sulfite can be replaced by the corresponding magnesium, zinc, or calcium salts without any noticeable difference being observed. 

In Zygosaccharomyces rouxii, one of the few salt-tolerant yeasts, the amount of free ergosterol in the membrane of cells grown in 15% NaCl increased 2.9-fold over that in control cells. This increase could have contributed (together with the decrease of fatty acid unsaturation) to the observed loss of membrane fluidity. Such a modification would facilitate... 

Hosono K. The release of proteins and UV-absorbing materiak from salt-tolerant yeast, Zygosaccharo-myces rouxii, by osmotic shock.J Ferment Bioeng 1991 72 445. 

C. Chan, M. Lehmann, K. Tag, K.M. Lung, G. Kunze, K. Reidel, B. Gruendig, and R. Rermeberg. Measurement of biodegradable substances using the salt-tolerant yeast Arxula adeninivorans for a microbial sensor immobilized with poly(carbamoyl)sulfonate (PCS). Part I. Construction and characterisation of the microbial sensor. Biosens. Bioelectron., 14 131-138,1999. 

De-novo fermentation of ASA in an acid-tolerant yeast, combined with in-pro-cess product removal, has the potential of eliminating salt production altogether. Unfortunately, there is no microbe that naturally produces ASA and the reported yields are minute until now [176]. 

There are, however, several complications. The terms halophilic and osmophilic already suggest that different substances have different effects. Halophilic bacteria can tolerate a high concentration of salts, but not of sugars, and it is the other way round for osmophilic yeasts. Table 8.1 gives some examples of the lowest aw tolerated, when caused by various components. It is seen that the variation is considerable, by a factor of 5 in (1 — aw). This implies that the components have specific effects. Ethanol and glycerol cannot be kept out of the cell by most organisms, and thus do not cause an osmotic pressure difference over the cell membrane. 

Halophilic yeasts were isolated from the Antarctic lake, Don Juan. Halo-tolerant yeast species, Debaryomyces hansenii, and osmotolerant Saccha-romyces rouxii are known. A hyphomycete, Cladosporium sp., was found to grow in wood panels submerged in north-end water from the Great Salt Lake. Because of the extensive development and the fact that the salinity remained at 29% or higher, it seems clear that this fungus developed under extremely halophilic conditions [62]. 

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