Influence of Calcium Ion on Ethanol Tolerance of Saccharomyces bayanus and Alcoholic Fermentation by Yeasts

The addition of Ca²⁺ (as CaCl₂) in optimal concentrations (0.75 to 2.0 mM) to a fermentation medium with a trace contaminating concentration of Ca²⁺ (0.025 mM) led to the rapid production of higher concentrations of ethanol by Saccharomyces cerevisiae, Saccharomyces bayanus, and Kluyveromyces marxianus. The positive effect of calcium supplementation (0.75 mM) on alcoholic fermentation by S. bayanus was explained by the increase in its ethanol tolerance. The ethanol inhibition of growth and fermentation followed the equation μ_xi = μ_oi [1 - (X/X_mi)]ⁿⁱ, where μ_oi and μ_xi are, respectively, the specific growth (i = g) and fermentation (i = f) rates in the absence or presence of a concentration (X) of added ethanol, and X_mi is the maximal concentration of ethanol which allows growth or fermentation. The toxic power is given by n_i. In Ca²⁺ - supplemented medium (0.75 mM), n_g = 0.42 for growth and n_f = 0.43 for fermentation compared with 0.52 and 0.55, respectively, in unsupplemented medium; for both media, X_mg = 10% (vol/vol) and X_mf = 13% (vol/vol). For lethal concentrations of ethanol, the specific death rates were minimal for cells that were grown and incubated with ethanol in medium with an optimal concentration of Ca²⁺, maximal for cells grown and incubated with ethanol in unsupplemented medium, and intermediate for cells grown in unsupplemented medium and incubated with ethanol in calcium-supplemented medium. The effect of Ca²⁺ on the acidification curve of energized cells in the presence of ethanol was found to be closely associated with its protective effect on growth, fermentation, and viability.     

Radial distribution of Ni in stemwood of Quercus ilex L. trees grown on serpentine and sandy loam (umbric leptosol) soils of NE-Portugal

Concentrations of Ni were determined in xylem and phloem of Quercus ilex trees growing on serpentine and sandy loam soils of northeast Portugal. Radial distribution patterns of Ni in stemwood were compared to variations in annual growth increments of the trees.Concentrations of Ni in xylem and phloem were higher in Q. ilex from serpentine soil, when compared with Q. ilex of a sandy loam soil.The radial distributions of Ni showed large variations among the trees, although they all grew in the same area within a short distance from each other. These differences can be caused by small-scale spatial variations in the soil. Therefore, the use of such radial Ni distributions for a retrospective biomonitoring of the Ni pollution of larger areas appears questionable.     

Phylogeny of Greya (Lepidoptera: Prodoxidae), based on nucleotide sequence variation in mitochondrial cytochrome oxidase I and II: congruence with morphological data

The phylogeny of Greya Busck (Lepidoptera: Prodoxidae) was inferred from nucleotide sequence variation across a 765-bp region in the cytochrome oxidase I and II genes of the mitochondrial genome. Most parsimonious relationships of 25 haplotypes from 16 Greya species and two outgroup genera (Tetragma and Prodoxus) showed substantial congruence with the species relationships indicated by morphological variation. Differences between mitochondrial and morphological trees were found primarily in the positions of two species, G. variabilis and G. pectinifera, and in the branching order of the three major species groups in the genus. Conflicts between the data sets were examined by comparing levels of homoplasy in characters supporting alternative hypotheses. The phylogeny of Greya species suggests that host-plant association at the family level and larval feeding mode are conservative characters. Transition/transversion ratios estimated by reconstruction of nucleotide substitutions on the phylogeny had a range of 2.0-9.3, when different subsets of the phylogeny were used. The decline of this ratio with the increase in maximum sequence divergence among taxa indicates that transitions are masked by transversions along deeper internodes or long branches of the phylogeny. Among transitions, substitutions of A-->G and T-->C outnumbered their reciprocal substitutions by 2-6 times, presumably because of the approximately 4:1 (77%) A+T-bias in nucleotide base composition. Of all transversions, 73%-80% were A<-->T substitutions, 85% of which occurred at third positions of codons; these estimates did not decrease with an increase in maximum sequence divergence of taxa included in the analysis. The high frequency of A<-->T substitutions is either a reflection or an explanation of the 92% A+T bias at third codon positions.