M. J. Almeida

Small heat-shock protein Hsp12 contributes to yeast tolerance to freezing stress

The HSP12 gene encodes one of the two major small heat-shock proteins of Saccharomyces cerevisiae and is induced under different conditions, such as low and high temperatures, osmotic or oxidative stress and high sugar or ethanol concentrations. However, few studies could demonstrate any correlation between HSP12 deletion or overexpression and a phenotype of sensitivity/resistance, making it difficult to attribute a role for Hsp12p under several of these stress conditions. We investigated the possible role of Hsp12p in yeast freezing tolerance. Contrary to what would be expected, the hsp12 null mutant when subjected to prolonged storage at -20 degrees C showed an increased resistance to freezing when compared with the isogenic wild-type strain. Because the mutant strain displayed a higher intracellular trehalose concentration than the wild-type, which could mask the effect of manipulating HSP12, we overexpressed the HSP12 gene in a trehalose-6-phosphate synthase (TPS1) null mutant. The tps1Delta strain overexpressing HSP12 showed an increase in resistance to freezing storage, indicating that Hsp12p plays a role in freezing tolerance in a way that seems to be interchangeable with trehalose. In addition, we show that overexpression of HSP12 in this tps1Delta strain also increased resistance to heat shock and that absence of HSP12 compromises the ability of yeast cells to accumulate high levels of trehalose in response to a mild heat stress.

Characterization of the yeast population from traditional corn and rye bread doughs

M.J. ALMEIDA AND C.S. PAIS. 1996. Yeasts were isolated from a variety of home‐made bread doughs and identified. A pure culture of Saccharomyces cerevisiae was found in 18% of the doughs. The same species predominated in 80% of the doughs examined whereas Issatchenkia orientalis, Pichia membranaefaciens and Torulaspora delbrueckii were present in about 40% of the samples. About one quarter of the isolates displayed killer activity, strains of P. anomala showing the broadest spectra. Two isolates of S. cerevisiae and three of T. delbrueckii gave biomass values in sucrose medium similar to or higher than those obtained with commercial compressed bakers yeast strains.

Rosmarinic acid, major phenolic constituent of Greek sage herbal tea, modulates rat intestinal SGLT1 levels with effects on blood glucose

SCOPE Previous results suggested that the effects of Salvia fruticosa tea (SFT) drinking on glucose regulation might be at the intestinal level. Here we aim to characterize the effects of SFT treatment and of its main phenolic constituent--rosmarinic acid (RA)--on the levels and localization of the intestinal Na+/glucose cotransporter-1 (SGLT1), the facilitative glucose transporter 2 and glucagon-like peptide-1 (GLP-1). METHODS AND RESULTS Two models of SGLT1 induction in rats were used: through diabetes induction with streptozotocin (STZ) and through dietary carbohydrate manipulation. Drinking water was replaced with SFT or RA and blood parameters, liver glycogen and the levels of different proteins in enterocytes quantified. Two weeks of SFT treatment stabilized fasting blood glucose levels in STZ-diabetic animals. The increase in SGLT1 localized to the enterocyte brush-border membrane (BBM) induced by STZ treatment was significantly abrogated by treatment with SFT, without significant changes in total cellular transporter protein levels. No effects were observed on glucose transporter 2, Na(+) /K(+) -ATPase or glucagon-like peptide-1 levels by SFT. Additionally, SFT and RA for 4 days significantly inhibited the carbohydrate-induced adaptive increase of SGLT1 in BBM. CONCLUSION SFT and RA modulate the trafficking of SGLT1 to the BBM and may contribute to the control of plasma glucose.

Improved gene disruption method for Torulaspora delbrueckii

PCR-based disruption cassettes are one of the most commonly used strategies for gene targeting in Saccharomyces cerevisiae. The efficiencies of gene disruption using this conventional method are highly variable among species, and often quite low with nonconventional yeasts. Here we describe an improved strategy to obtain deletion mutants in bakers yeast Torulaspora delbrueckii, one of the most abundant non-Saccharomyces species, present in home-made corn and rye bread dough.

Salvia fruticosa tea drinking reduces the expression of sodium/glucose cotransporter 1 in enterocytes brush-border membrane of streptozotocin-induced diabetic rats

Diabetes mellitus is a metabolic disorder characterised by elevated plasma glucose concentrations, resulting from insufficient insulin secretion, insulin resistance or both. The prevalence of Type 2 diabetes mellitus is increasing worldwide and 366 million diabetic people are expected by 2030 [1]. Considering this increase in the prevalence of this disorder and a lack of an efficient treatment, there is a growing interest on the research of new bioactive compounds. One of the features of type 2 diabetes mellitus (T2DM) is an increase in Na+-dependent glucose transporter (SGLT1) expression in the brush-border membrane (BBM) of the enterocyte. This increases intestinal glucose absorption and aggravates hyperglycaemia [2]. Moreover, secretion of glucagon-like peptide1 (GLP-1), one of the enteroendocrine incretin hormones, and levels of insulin are reduced under a diabetic condition [3]. Salvia fruticosa is a medicinal plant to which antidiabetic properties have been attributed [4,5] and our previous results suggested an effect on control of blood glucose by reducing SGLT1 expression in brush-border membrane vesicles (BBMV) of rats after diet manipulation (unpublished data). In an attempt to characterise the antidiabetic effects of sage tea at the levels of intestinal epithelium and insulin secretion, normal and streptozotocin (STZ)-induced diabetic rats were used. S. fruticosa tea was given ad libitum, instead of water, for 14 days to the treated animals. Enterocyte SGLT1 and facilitative glucose transporter 2 (GLUT2) expression were evaluated by Western blotting. Effects on GLP-1 and islet regeneration (β cell insulin expression) were assessed by immunohistochemistry.