Active glycerol uptake is a mechanism underlying halotolerance in yeasts: a study of 42 species

Abstract

A comparison of 42 yeast species with respect to growth in the presence of high NaCl concentration and characteristics of glycerol uptake is presented. The yeast species were classified into four classes on the basis of their ability to grow in the presence of 1, 2, 3 or 4 M NaCl. Considering that two different types of active-transport systems for glycerol uptake have been described, Na M /glycerol and H M /glycerol symports, glycerol transport was investigated by testing for proton uptake upon glycerol addition in cells incubated in the absence and in the presence of NaCl. Only strains belonging to the two higher classes of salt tolerance showed constitutive active glycerol uptake, and could accumulate glycerol internally against a concentration gradient. Five of these strains exhibited a H M /glycerol symport. All the other strains showed evidence of the activity of a salt-dependent glycerol uptake similar to that described in the literature for Debraryomyces hansenii. The strains within the two lower classes of salt tolerance showed, to varying degrees, glycerol active uptake only when glycerol was used as the carbon and energy source, suggesting that this uptake system is involved in glycerol catabolism. The results within this work suggest that active glycerol uptake provides a basis for high halotolerance, helping to maintain a favourable intracellular concentration of glycerol. The relation between the constitutive expression of such carriers and a higher level of salt-stress resistance suggests that this may be an evolutionary advantage for growth under such conditions.

New insights on glycerol transport in Saccharomyces cerevisiae

“…This points to the possibility of Gup1p and Gup2p not being glycerol carriers, but, instead, regulatory proteins, since they do interfere with transport activity [6]. This hypothesis is consistent with the GUP1 and GUP2 low and constitutive expression [7] and with the observation that the presence of GUP1 homologues in several yeasts [8] does not correlate to the detection of H þ /glycerol symport activity [8,9]. We thus suggest for Gup1p and Gup2p roles other than glycerol active transport, being the gene encoding for glycerol active transport yet unknown.…”

“…not vary with extracellular pH. This is considered as an indirect consequence of the active transport responsible for accumulation against chemical gradient being dependent on proton-motive force [5,9,13]. Also, variation of NaCl concentration in assay buffer did not affect accumulation rates significantly.…”

“…Further studies on GUP1 and GUP2 expression have shown these genes to be very low and constitutive, and no correlation was found between GUP1 and GUP2 expression, glycerol intracellular levels and glycerol active transport detection [7]. Moreover, the high similarity between GUP1-like sequences from different yeast species [8] is not consistent with the detection of glycerol active transport in the same species [9]. Also, and despite that these genes were attributed an exclusive family in the Transport Protein database (TC-DB2.A.50.1.1), they were preferentially included in a superfamily of membranebound O-acyl transferases (MBOAT/DltB/KOG3860) [10].…”

“…Initial rates of glycerol uptake, external alkalinization upon glycerol addition, as well as in/out accumulation ratios, were determined as previously described [5,9,12,13]. The intracellular volume values used to determine intracellular glycerol molarity have been determined by Lages and Lucas [5].…”

SÍNTESE, CARACTERIZAÇÃO E DEGRADAÇÃO DE P(3HB) POR Cupriavidus necator UTILIZANDO GLICEROL COMO SUBSTRATO

“…É um composto com grande importância dentro do sistema metabólico de microorganismos, atuando como precursor de numerosos compostos e como regulador de vários mecanismos bioquímicos intracelulares (LAGES et al, 1999).…”