The expanding large-spored Metschnikowia clade: Metschnikowia matae sp. nov., a yeast species with two varieties from the Brazilian Atlantic Forest.

Fifty-two yeast isolates from flowers and associated nitidulid beetles of the Brazilian Atlantic Forest (Mata Atlântica) region were found to represent a new species in the large-spored Metschnikowia clade. The species is heterothallic, haploid, and allogamous, and produces asci with two aciculate ascospores that can reach 80 µm in length, as is typical in the clade. Analysis of sequences of the ribosomal RNA gene cluster indicates that the new species is closely related to Metschnikowia lochheadii, which ranges across Central America to northern Brazil, occurs as an adventive species in Hawaii, but is rarely found in central Brazil. The species is not readily distinguishable from relatives based on morphology or growth responses, but is well delineated from M. lochheadii on reproductive isolation. Based on an intron splice site PCR screen, we selected 26 isolates for further study. The sequence of the region that includes the complete internal transcribed spacer/5.8S rRNA gene segment as well as the D1/D2 domains of the large subunit rRNA gene contained three polymorphic segments and 14 haplotypes were identified. Of these, a single divergent isolate from the southernmost of four sampled localities exhibited diminished mating success when crossed with others. We describe two varieties, Metschnikowia matae var. matae sp. nov. var. nov. (type UFMG-CM-Y395(T), CBS 13986(T), NRRL Y-63736(T); allotype UFMG-CM-Y391(A), CBS 13987(A), NRRL Y-63735(A)) and Metschnikowia matae var. maris sp. nov. var. nov. (type UFMG-CM-Y397(T), CBS 13985(T), NRRL Y-63737(T)). We also report on the discovery of the h (+) mating type of Candida ipomoeae and transfer of the species to Metschnikowia ipomoeae comb. nov. (allotype UWOPS 12-660.1(A), CBS 13988(A), NRRL Y-63738(A)).

Yeast biomass production: a new approach in glucose-limited feeding strategy.

The aim of this work was to implement experimentally a simple glucose-limited feeding strategy for yeast biomass production in a bubble column reactor based on a spreadsheet simulator suitable for industrial application. In biomass production process using Saccharomyces cerevisiae strains, one of the constraints is the strong tendency of these species to metabolize sugars anaerobically due to catabolite repression, leading to low values of biomass yield on substrate. The usual strategy to control this metabolic tendency is the use of a fed-batch process in which where the sugar source is fed incrementally and total sugar concentration in broth is maintained below a determined value. The simulator presented in this work was developed to control molasses feeding on the basis of a simple theoretical model in which has taken into account the nutritional growth needs of yeast cell and two input data: the theoretical specific growth rate and initial cell biomass. In experimental assay, a commercial baker's yeast strain and molasses as sugar source were used. Experimental results showed an overall biomass yield on substrate of 0.33, a biomass increase of 6.4 fold and a specific growth rate of 0.165 h(-1) in contrast to the predicted value of 0.180 h-1 in the second stage simulation.

Yeast biomass production: a new approach in glucose-limited feeding strategy

The aim of this work was to implement experimentally a simple glucose-limited feeding strategy for yeast biomass production in a bubble column reactor based on a spreadsheet simulator suitable for industrial application. In biomass production process using Saccharomyces cerevisiae strains, one of the constraints is the strong tendency of these species to metabolize sugars anaerobically due to catabolite repression, leading to low values of biomass yield on substrate. The usual strategy to control this metabolic tendency is the use of a fed-batch process in which where the sugar source is fed incrementally and total sugar concentration in broth is maintained below a determined value. The simulator presented in this work was developed to control molasses feeding on the basis of a simple theoretical model in which has taken into account the nutritional growth needs of yeast cell and two input data: the theoretical specific growth rate and initial cell biomass. In experimental assay, a commercial baker's yeast strain and molasses as sugar source were used. Experimental results showed an overall biomass yield on substrate of 0.33, a biomass increase of 6.4 fold and a specific growth rate of 0.165 h-1 in contrast to the predicted value of 0.180 h-1 in the second stage simulation.

Study of flocculent yeast performance in tower reactors for bioethanol production in a continuous fermentation process with no cell recycling.

The purpose of this study was to assess the retention ability of 12 different Saccharomyces sp. yeast strains with flocculent characteristics when inoculated in a continuous ethanol fermentation process. The system was comprised of two reactors connected in series with no cell recycling. The feeding substrate used was a synthetic medium containing glucose. The parameters assessed were total reducing sugars of the feeding substrate, total reducing sugars and ethanol at the outlet of the first and second reactors and quantification and classification of yeast population in the two reactors. The system reached yield levels of 83.53% of theoretical yield with a maximum total reducing sugars conversion of 92.68%. The conversion in this system was lower than expected. The dominant yeast in the process in both reactors, contrary to expectation, was the Saccharomyces CP6 strain which was unable to form pellets in spite of its flocculate growth.