Genetic analysis of apomictic wine yeasts.

The Saccharomyces cerevisiae wine yeast IFI256 was selected because of its high fermentative capacity and tolerance to ethanol. Sporulation of the IFI256 strain produced two-spore asci unable to conjugate, but able to sporulate again and the spores produced two-spore asci in all cases. That process was studied for at least five generations. The electrophoretic karyotype showed a pattern of 21 chromosomal bands, which was identical both in the parental and in all the descendants analyzed, from the first to the fifth generation. The DNA content of the parental and the descendants was of 1.7 n, which indicates that the capacity for sporulation shown by all descendants was due to apomixis rather than homothallism of the strain. Different concentrations of glucose and acetate and the addition of zinc salts to the presporulation and sporulation media increased the frequency of four-spore asci by up to 9%. However, the tetrads formed were in fact two dyads that resulted from induced endomitosis. Crosses of IFI256 with laboratory strains produced hybrids giving four-spore asci after sporulation, thus indicating the mutation to be recessive. Transformation of IFI256 with plasmids carrying either SPO12 or SPO13 functional genes and crosses with strains carrying functional or mutated SPO12 and/or SPO13 genes indicated that IFI256 carries several mutations, one of which was located to the SPO12 gene. Parasexual cycles and chromosome loss induced after crossing IFI256 with cir0 strains indicated that apomictic mutations were exclusively located at chromosome VIII. The high frequency of wine strains which are apomictic suggests apomixis to be an advantageous phenotype which allows the formation of stress-resistant asci but prevents the loss of favored chromosomal rearrangements.

Repellence of boophilus microplus larvae in stylosanthes humilis and Stylosanthes hamata plants

El objetivo de este estudio fue investigar la repelencia de larvas de B. microplus presente en las leguminosas tropicales Stylosanthes humilis y S. hamata, e identificar algunos de los compuestos químicos presentes en ambas leguminosas. El efecto fue evaluado mediante un bioensayo de repelencia con un olfactómetro utilizando extractos de hojas, tallos y de la planta completa, tratados con diferentes solventes orgánicos como hexano, acetona, cloroformo y metanol. La identificación de los compuestos químicos se realizó mediante cromatografía de gases - espectrofotometría de masas en extractos de planta completa. Este estudio demostró que ambas leguminosas tropicales tienen importantes propiedades de repelencia, ésta se ubicó en un rango de 68 por ciento a 92 por ciento en S. humilis, y entre 70 por ciento y 82 por ciento en S. hamata. Dieciséis compuestos químicos fueron identificados en S. humilis, siendo ferroceno y beta sitosterol los más abundantes (18,3 por ciento y 14 por ciento). Diecisiete compuestos fueron identificados en S. hamata siendo el ác. Linolenico el que tuvo la más alta abundancia relativa (17,6 por ciento). Los compuestos identificados pueden ser considerados posibles candidatos para explicar el efecto repelente de estas plantas.

New Saccharomyces cerevisiae baker's yeast displaying enhanced resistance to freezing.

Three procedures were used to obtain new Saccharomyces cerevisiae baker's yeasts with increased storage stability at -20, 4, 22, and 30 degrees C. The first used mitochondria from highly ethanol-tolerant wine yeast, which were transferred to baker's strains. Viability of the heteroplasmons was improved shortly after freezing. However, after prolonged storage, viability dramatically decreased and was accompanied by an increase in the frequency of respiratory-deficient (petite) mutant formation. This indicated that mitochondria were not stable and were incompatible with the nucleus. The strains tested regained their original resistance to freezing after recovering their own mitochondria. The second procedure used hybrid formation after protoplast fusion and isolation on selective media of fusants from baker's yeast meiotic products resistant to parafluorphenylalanine and cycloheximide, respectively. No hybrids were obtained when using the parentals, probably due to the high ploidy of the baker's strains. Hybrids obtained from nonisogenic strains manifested in all cases a resistance to freezing intermediate between those of their parental strains. Hybrids from crosses between meiotic products of the same strain were always more sensitive than their parentals. The third method was used to develop baker's yeast mutants resistant to 2-deoxy-d-glucose (DOG) and deregulated for maltose and sucrose metabolism. Mutant DOG21 displayed a slight increase in trehalose content and viability both in frozen doughs and during storage at 4 and 22 degrees C. This mutant also displayed a capacity to ferment, under laboratory conditions, both lean and sweet fresh and frozen doughs. For industrial uses, fermented lean and sweet bakery products, both from fresh and frozen doughs obtained with mutant DOG21, were of better quality with regard to volume, texture, and organoleptic properties than those produced by the wild type.

Acetaldehyde and ethanol are responsible for mitochondrial DNA (mtDNA) restriction fragment length polymorphism (RFLP) in flor yeasts.

Flor yeasts grow and survive in fino sherry wine where the frequency of respiratory-deficient (petite) mutants is very low. Mitochondria from flor yeasts are highly acetaldehyde- and ethanol-tolerant, and resistant to oxidative stress. However, restriction fragment length polymorphism (RFLP) of mtDNA from flor yeast populations is very high and reflects variability induced by the high concentrations of acetaldehyde and ethanol of sherry wine on mtDNA. mtDNA RFLP increases as the concentration of these compounds also increases, but is followed by a total loss of mtDNA in petite cells. Yeasts with functional mitochondria (grande) are target of continuous variability, so that flor yeast mtDNA can evolve extremely rapidly and may serve as a reservoir of genetic diversity, whereas petite mutants are eventually eliminated because metabolism in sherry wine is oxidative.