Sympodiomyces attinorum sp. nov., a yeast species associated with nests of the leaf-cutting ant Atta sexdens.

Four strains of a novel yeast species were isolated from laboratory nests of the leaf-cutting ant Atta sexdens in Brazil. Three strains were found in older sponges and one was in a waste deposit in the ant nests. Sequencing of the D1/D2 region of the large-subunit rRNA gene showed that the novel species, named Sympodiomyces attinorum sp. nov., is phylogenetically related to Sympodiomyces parvus. Unlike Sympodiomyces parvus, Sympodiomyces attinorum can ferment glucose, assimilate methyl alpha-D-glucoside, salicin and citrate, and grow at 37 degrees C, thus enabling these two species to be distinguished. Differentiation from other related species is possible on the basis of other growth characteristics. The type strain of Sympodiomyces attinorum is UNESP-S156T (= CBS 9734T = NRRL Y-27639T).

Colorimetric determination of active alpha-glucoside transport in Saccharomyces cerevisiae.

Fermentation of alpha-glucosides (maltose, maltotriose) by Saccharomyces cerevisiae cells is a critical phase in the processes of brewing and breadmaking. Utilization of alpha-glucosides requires the active transport of the sugar across the cell membrane and, subsequently, its hydrolysis by cytoplasmic glucosidases. Although transport activities are usually assayed using radiolabeled substrates, we have developed a simple, cheap and reliable colorimetric assay for the determination of alpha-glucoside uptake using p-nitrophenyl-alpha-D-glucopyranoside (pNPalphaG) as substrate. Our results show that pNPalphaG is actively transported by S. cerevisiae cells by a H+-symport mechanism, which depends on the electrochemical proton gradient across the plasma membrane. pNPalphaG uptake is mediated by the AGT1 alpha-glucoside permease, which has a high affinity (Km=3 mM) for this chromogenic substrate. This simple colorimetric uptake assay can be used to analyze the expression and regulation of the AGT1 permease in S. cerevisiae cells.

Kinetics of active alpha-glucoside transport in Saccharomyces cerevisiae.

alpha-Glucosides are the most abundant fermentable sugars in the industrial applications of Saccharomyces cerevisiae, and the active transport across the plasma membrane is the rate-limiting step for their metabolism. In this report we performed a detailed kinetic analysis of the active alpha-glucoside transport system(s) present in a wild-type strain, and in strains with defined alpha-glucoside permeases. Our results indicate that the wild-type strain harbors active transporters with high and low affinity for maltose and trehalose, and low-affinity transport systems for maltotriose and alpha-methylglucoside. The maltose permease encoded by the MAL21 gene showed a high affinity (K(m) approximately 5 mM) for maltose, and a low affinity (K(m) approximately 90 mM) for trehalose. On the other hand, the alpha-glucoside permease encoded by the AGT1 gene had a high affinity (K(m) approximately 7 mM) for trehalose, a low affinity (K(m) approximately 18 mM) for maltose and maltotriose, and a very low affinity (K(m) approximately 35 mM) for alpha-methylglucoside.

Active alpha-glucoside transport in Saccharomyces cerevisiae.

The AGT1 permease is a alpha-glucoside-H+ symporter responsible for the active transport of maltose, trehalose, maltotriose, alpha-methylglucoside, melezitose and sucrose. In wild-type as well as in MAL constitutive strains, alpha-methylglucoside seemed to be the best inducer of transport activity, while trehalose had no inducing effect. Based on the initial rates of transport it seems that the sugar preferentially transported by this permease is trehalose, followed by sucrose.

Production of amylase by Aspergillus fumigatus utilizing alpha-methyl-D-glycoside, a synthetic analogue of maltose, as substrate.

A strain of Aspergillus fumigatus isolated from soil was able to produce biomass and high amylase activities in media containing alpha-methyl-D-glucoside (alphaMG), a synthetic analogue of maltose, as the only carbon source. alphaMG was a more effective inducer than starch and maltose at the same concentration: alphaMG cultures produced about 3 times more alpha-amylase and glucoamylase activity than starch cultures. Maximum production of alpha-amylase (60 U/mg) and glucoamylase (130 U/mg) was obtained in 8-10 days alphaMG cultures.

Effect of atrial natriuretic peptide on alpha-methyl-D-glucoside intestinal active uptake in rats.

In vivo, atrial natriuretic peptide (ANP) inhibits water and sodium absorption by the intestine. In addition, ANP inhibits glucose (re)absorption at the level of both the intestine and kidney. ANP also decreases sodium absorption in the rat small intestine in vitro, but only if glucose is present on the luminal side of the tissue. These findings suggest that ANP inhibits the sodium-glucose cotransporter (SGLT) of enterocytes. In the present study the inhibitory effect of 1 microM ANP on SGLT1 in rat small intestine and colon was tested. For this purpose, the apparent kinetic constants of SGLT1 were determined using radioactive alpha-methyl-D-glucoside (alpha-MG), a non-metabolizable glucose analogue that selectively serves the luminal Na+-dependent intestinal uptake, but not the serosal-facilitated diffusion sugar carrier. In both tissues, incubation with ANP increased Km without modifying the Vmax. In addition, Vmax in the small intestine was found to be higher than in the colon. The evidence presented here suggests that ANP, through its second messenger, may be a competitive inhibitor of SGLT1. Since SGLT1 is also expressed in the brush-border membrane of the renal proximal tubule, we suggest that this peptide might regulate the hydro-saline balance at intestinal and proximal tubular nephron levels.

[Candida dubliniensis: 1st isolation in Argentina]. / Candida dubliniensis: primer aislamiento en Argentina.

We report the first isolation of Candida dubliniensis in Argentina. This strain was isolated from an oral lesion of an adult patient with AIDS during one recurrent episode of a previously treated oropharingeal candidosis. Phenotypic and genotypic characteristics coincided with those described by Sullivan et al., who was the first to study this new species.

Use of tests for acidification of methyl-alpha-D-glucopyranoside and susceptibility to efrotomycin for differentiation of strains of Enterococcus and some related genera.

A total of 107 Enterococcus strains, 10 Vagococcus fluvialis strains, and 8 Lactococcus garvieae strains were tested for acidification of methyl-alpha-D-glucopyranoside (MGP) and susceptibility to 100-microg efrotomycin (EFRO) disks. All 26 strains of Enterococcus casseliflavus, including 3 nonmotile and 2 nonpigmented strains, acidified MGP and were resistant to EFRO. All 22 strains of Enterococcus gallinarum, including 5 nonmotile strains, also acidified MGP and were resistant to EFRO. None of the 26 strains of Enterococcus faecium acidified MGP, and all were susceptible to EFRO. Although all 12 Enterococcus faecalis strains were also negative in the MGP test, they were resistant to EFRO. Other enterococcal strains gave variable results. All 10 strains of V. fluvialis and all 8 strains of L. garvieae gave positive and negative results, respectively, in the MGP test and were, respectively, resistant and susceptible to EFRO. These results indicate that tests of the production of acid from MGP and susceptibility to EFRO can be used as adjunct tests in the identification of typical and atypical strains of enterococci in the clinical microbiology laboratory.

Stimulation-enhanced 3-O-methylglucose efflux from the frog sartorius: kinetics and properties of the system.

The characteristics of the process by which contraction enhances glucose transport in the frog sartorius were studied. Electrical stimulation increased the permeability of muscles to 3-O-methylglucose (3-O-MeGlc), a nonmetabolizable glucose analogue, increasing efflux as well as uptake. Enhanced efflux was due to an increase in Vmax of the efflux process. A lactacidosis had no effect on basal 3-O-MeGlc efflux, and replacement of media Na+ with Li+ did not affect stimulation-induced uptake. Also, basal and stimulated uptake was not affected by 1 microM 12-O-tetradecanoylphorbol-13-acetate (TPA), a protein kinase C activator. Lastly, N-carbobenzoxy-glycyl-L-phenylalaninamide, which inhibits insulin-enhanced, but not basal, glucose uptake in adipocytes, inhibited both basal and stimulated 3-O-MeGlc fluxes in the frog sartorius. From these findings, we conclude: (1) contraction and exercise enhance glucose transport in muscle by increasing the number of transporters in the plasma membrane, or their turnover, by an unknown process; and (2) basal glucose transport of muscle, unlike that of adipocytes, can not be distinguished from stimulated transport on the basis of its insensitivity to N-carbobenzoxyglycyl-L-phenylalaninamide.