Yeasts in Hevea brasiliensis Latex.

Yeast abundance and species diversity in the latex of caoutchouc tree Hevea brasiliensis (Willd. ex Juss.) M611. Arg., on its green leaves, and in soil below the plant Was studied. The yeasts present in the fresh latex in concentrations of up to 5.5 log(CFU/g) were almost exclusively represented by the species Candida heveicola, which was previously isolated from Hevea latex in China. In the course of natural modification of the latex yeast diversity increased, while yeast abundance decreased. The yeasts of thickened and solidified latex were represented by typical epiphytic and ubiquitous species: Kodamea ohmeri, Debaryomyces hansenii, Rhodotorula mucilaginosa, and synanthropic species Candida parapsilosis and Cutaneotrichosporon arbori- formis. The role of yeasts in latex modification at the initial stages of succession and their probable role in de- velopment of antifungal activity in the latex are discussed.

Characterization of new polyol/H+ symporters in Debaryomyces hansenii.

Debaryomyces hansenii is a halotolerant yeast that produces and assimilates a wide variety of polyols. In this work we evaluate polyol transport in D. hansenii CBS 767, detecting the occurrence of polyol/H(+) (and sugar/H(+)) symporter activity, through the transient extracellular alkalinization of unbuffered starved cell suspensions. From the D. hansenii genome database, we selected nine ORFs encoding putative transporter proteins to clone in a centromeric plasmid with C-terminal GFP tagging and screened for polyol/H(+) symporters by heterologous expression in Saccharomyces cerevisiae. Five distinct D. hansenii polyol/H(+) symporters were identified and characterized, with different specificities and affinities for polyols, namely one glycerol-specific (DhStl1), one D-galactitol-specific (DhSgl1, Symporter galactitol/H(+) 1), one D-(+)-chiro-inositol-specific (DhSyi1, Symporter D-(+)-chiro-inositol/H(+) 1), one for D-sorbitol/D-mannitol/ribitol/D-arabitol/D-galactitol (DhSyl1, Symporter Polyols 1) and another for D-sorbitol/D-mannitol/ribitol/D-arabitol (DhSyl2, Symporter Polyols 2). This work contributed to the annotation of new yeast polyol transporters, including two specific for uncommon substrates as galactitol and D-(+)-chiro-inositol.

BOD biosensor based on the yeast Debaryomyces hansenii immobilized in poly(vinyl alcohol) modified by N-vinylpyrrolidone.

An amperometric biosensor for assessing the biochemical oxygen demand (BOD) was formed by immobilizing Debaryomyces hansenii VKM Y-2482 yeast cells in poly(vinyl alcohol) modified by N-vinylpyrrolidone. Modification provided for a high sensitivity and stability of the bioreceptor. A high oxidative activity of the receptor element and the absence of any toxic effect of assayed compounds were shown for 34 substrates (alcohols, carbohydrates, carboxylic acids, amino acids, nitrophenols and surfactants) that may occur in wastewaters. Estimates of the measurement range and region of the linear dependence of signals on the BOD level, pH and temperature sensitivities, dependences of signals on concentrations of salts, stability, Michaelis kinetic constants and assay rates were obtained. The BOD values determined by the biosensor in assayed wastewater samples were shown to have a high correlation with those obtained by the standard dilution method.

Enhanced ethanol production from wheat straw by integrated storage and pre-treatment (ISP).

Integrated storage and pre-treatment (ISP) combines biopreservation of moist material under airtight conditions and pre-treatment. Moist wheat straw was inoculated with the biocontrol yeast Wickerhamomyces anomalus, the xylan degrading yeast Scheffersomyces stipitis or a co-culture of both. The samples and non-inoculated controls were stored at 4 or 15 °C. The non-inoculated controls were heavily contaminated with moulds, in contrast to the samples inoculated with W. anomalus or S. stipitis. These two yeasts were able to grow on wheat straw as sole source of nutrients. When ethanol was produced from moist wheat straw stored for four weeks at 4 °C with S. stipitis, an up to 40% enhanced yield (final yield 0.15 g ethanol per g straw dry weight) was obtained compared to a dry sample (0.107 g/g). In all other moist samples, stored for four weeks at 4 °C or 15 °C, 6-35% higher yields were obtained. Thus, energy efficient bio-preservation can improve the pre-treatment efficiency for lignocellulose biomass, which is a critical bottleneck in its conversion to biofuels.

Use of response surface methodology to evaluate the extraction of Debaryomyces hansenii xylose reductase by aqueous two-phase system.

Xylose reductase (XR) from Debaryomyces hansenii was extracted by partitioning in aqueous two-phase systems (ATPS) composed of polyethylene glycol (PEG) 4000 in the presence of different salts, specifically sodium sulfate, lithium sulfate and potassium phosphate. Batch extractions were carried out under different conditions of temperature (25-45 degrees C) and tie-line length (TLL) for each system, according to a central composite design face-centered of 36 tests, and the response surface methodology was used to evaluate the results. Quadratic polynomial models were adjusted to the data to predict the behavior of four responses, namely the XR partition coefficient (K(XR)), the selectivity (S), the purification factor (PF(T)) and the activity yield (Y(T)) in the top phase. The optimal extraction conditions were found using the PEG 4000/sodium sulfate system at 45 degrees C and TLL=25.1, which ensured PF(T)=3.1 and Y(T)=131%. The ATPS proved effective for partial purification of D. hansenii xylose reductase in cell-free crude extract, and the response surface methodology revealed to be an appropriate and powerful tool to determine the best dominion of temperature and ATPS composition.