Genetic diversity and population structure of Pichia guilliermondii over 400 generations of experimental microevolution

An in vitro evolution model was used to study changes in the genetic diversity of 24 strains of Pichia guilliermondii isolated from the midgut of bark beetles of the genus Dendroctonus . The genetic diversity of P. guilliermondii strains over 400 generations was analysed using multilocus enzyme electrophoresis (MLEE) and random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) markers. Resemblance relationships among strains were observed by cluster analysis. From the MLEE and RAPD markers, it was shown that the effective number of alleles, polymorphism and expected heterozygosity varied over the generations. The average heterozygosity among generations was statistically significant. Both the genetic diversity and the average heterozygosity were statistically significant among generations. The reduction in the population size from 10⁹ to 10⁵ yeast mL⁻¹ associated with each transfer in P. guilliermondii strains and the clonal population structure observed along 400 generations suggest that genetic diversity changes and the observed replacement of genotypes are a consequence of a genetic drift process and not of the reproductive mode.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 475–486.     

Kinetics of riboflavin production by Brewers'' yeasts

The kinetics of riboflavin production by Saccharomyces cerevisiae and Saccharomyces carlsbergensis in synthetic media and wort were studied. The results indicated that riboflavin was produced by growing cells only. Riboflavin production rate was proportional to growth rate of the yeasts in the exponential phase. Riboflavin was depleted in the stationary phase. The depletion rate was expressed with a first-order kinetic expression in yeast concentration. The kinetics of substrate utilization and ethanol production were also given to describe better the associated phenomena and fermentation pattern.     

Immunological comparison of microbial TPP-dependent non-oxidative α-keto acid decarboxylases

Abstract Antigenic, and hence possible evolutionary, relationships amongst various TPP-dependent non-oxidative α-keto acid decarboxylases were determined by the Ouchterlony double diffusion method and by measuring the degree of antibody-induced enzyme inhibition. The results show that: (a) phenylglyoxylate decarboxylases of various wild-type strains of Acinetobacter calcoaceticus are antigenically indistinguishable; (b) there seems to be no antigenic cross-reactivity between the phenylglyoxylate decarboxylase of A. calcoaceticus and of Pseudomonas aeruginosa or Pseudomonas putida ; and (c) no antigenic homology can be detected amongst phenylglyoxylate decarboxylase and phenylpyruvate decarboxylase of A. calcoaceticus and pyruvate decarboxylase of brewers' yeast.     

Screening recombinant phage M13 plaques with RNA probes; a one-step procedure which identifies clones containing either of the complementary DNA strands

We describe a method for detecting specific DNA sequences cloned in M13 phage vectors, based on the procedure of Woo (in Wu, R., Methods in Enzymology, Vol. 68, Academic Press, New York, 1979, pp. 389-395). M13 plaques are adsorbed to a nitrocellulose filter that has been pre-saturated with bacteria. The filter is incubated on an agar plate to amplify the phage; the DNA is alkali-denatured and then hybridized with a radioactive RNA probe. Unlike standard procedures, this method detects and distinguishes M13 plaques containing phage particles which harbor either the coding or non-coding (RNA-like) DNA strand, when single-stranded RNA is used as probe. We have optimized this procedure with M13 clones containing mouse histidine tRNA gene sequences and have used it to determine the sequence of both strands of a mouse glycine tRNA gene.     

Short Communication: Characterization and succession of yeast populations associated with spontaneous fermentations during the production of Brazilian sugar-cane aguardente

A succession of yeasts was observed during fermentation of aguardente with Saccharomyces cerevisiae being the predominant species. Candida sake, Kluyveromyces marxianus var. drosophilarum and apiculate yeasts were also frequent. Transient yeast species were found in variable numbers, probably due to the daily addition of sugar-cane juice. Killer yeasts were isolated and may have a role in the exclusion of some transient and contaminant species.     

Suppressor studies on ilvI mutants of Saccharomyces cerevisiae

In order to answer the question whether with the X-ray induction of an achromatic lesion (a gap) an increase of the chromatid length is involved (e.g. by a localized failure of spiralization), the length ratios of 26 straight and 22 flexed metaphase chromosomes of Vicia faba were measured. (The length ratio is defined as the quotient between the length of the chromatid with a gap and that of its sister-chromatid without a gap.) Our results agree with the hypothesis that the induction of a gap does not increase the length of the chromatid. Remarkably in each of the 22 flexed chromosomes the gap was located at the “outer” chromatid. The bearing of our results on the nature of X-ray-induced achromatic lesions is discussed.     

Loss of hydrazine-induced mutability in wild-type and excision-repair-defective yeast during post-treatment inhibition ofcell division.

The fate of presumed premutational DNA lesions induced by hydrazine was studied under a variety of post-treatment conditions in wild-type and in excision repair-defective (rad2-1) strains of Saccharomyces cerevisiae. In all strains the full extent of hydrazine-induced, forward mutability from CAN1 to can1 (canavanine resistance) was dependent upon post-treatment cell division in mutagen-free synthetic or complex growth medium before plating on canavanine-containing selective agar and could be blocked by inhibitors of DNA synthesis (hydroxyurea) or protein synthesis (cycloheximide) contained in the growth medium. Following the growth-inhibitory period, cells were permitted to grow in fresh medium lacking inhibitors to determine the level of induced mutation remaining. Nearly all induced mutability was lost after a one-day growth inhibition, compared with mutagen-treated control samples subsequently grown twice in medium lacking inhibitor. In the wild type, half the induced mutability was lost after 3 h. The data suggest that premutational DNA lesions induced by hydrazine were removed, or possibly rendered non-mutagenic, by some error-free repair process that acted before mutation fixation by base mispairing during DNA replication. Since rad2-1 and RAD strains both exhibited loss of mutability, this process is not dependent upon the activity of an intact pyrimidine dimer excision-repair system.