Bioethanol strains of Saccharomyces cerevisiae characterised by microsatellite and stress resistance

Abstract Strains of Saccharomyces cerevisiae may display characteristics that are typical of rough-type colonies, made up of cells clustered in pseudohyphal structures and comprised of daughter buds that do not separate from the mother cell post-mitosis. These strains are known to occur frequently in fermentation tanks with significant lower ethanol yield when compared to fermentations carried out by smooth strains of S. cerevisiae that are composed of dispersed cells. In an attempt to delineate genetic and phenotypic differences underlying the two phenotypes, this study analysed 10 microsatellite loci of 22 S. cerevisiae strains as well as stress resistance towards high concentrations of ethanol and glucose, low pH and cell sedimentation rates. The results obtained from the phenotypic tests by Principal-Component Analysis revealed that unlike the smooth colonies, the rough colonies of S. cerevisiae exhibit an enhanced resistance to stressful conditions resulting from the presence of excessive glucose and ethanol and high sedimentation rate. The microsatellite analysis was not successful to distinguish between the colony phenotypes as phenotypic assays. The relevant industrial strain PE-2 was observed in close genetic proximity to rough-colony although it does not display this colony morphology. A unique genetic pattern specific to a particular phenotype remains elusive.

Deterioration and fermentability of energy cane juice / Deterioração e fermentabilidade do caldo de cana energia

ABSTRACT: The main interest in the energy cane is the bioenergy production from the bagasse. The juice obtained after the cane milling may constitute a feedstock for the first-generation ethanol units; however, little attention has been dedicated to this issue. In order to verify the feasibility of the energy cane juice as substrate for ethanol production, the objectives of this research were first to determine the microbiological characteristics and deterioration along the time of the juices from two clones of energy cane (Type I) and second, their fermentability as feedstock for utilization in ethanol distilleries. There was a clear differentiation in the bacterial and yeast development of the sugarcane juices assayed, being much faster in the energy canes than in sugarcane. The storage of juice for 8 hours at 30oC did not cause impact in alcoholic fermentation for any sample analyzed, although a significant bacterial growth was detected in this period. A decrease of approximately seven percentage points in the fermentative efficiency was observed for energy cane juice in relation to sugarcane in a 24-hour fermentation cycle with the baking yeast. Despite the faster deterioration, the present research demonstrated that the energy cane juice has potential to be used as feedstock in ethanol-producing industries. As far as we know, it is the first research to deal with the characteristics of deterioration and fermentability of energy cane juices.

RESUMO: O principal interesse na cana energia reside na produção de bioenergia a partir do bagaço. O caldo obtido após a moagem da cana pode se constituir em substrato para as unidades de produção de etanol de primeira geração, no entanto, pouca atenção tem sido dispensada a esta questão. O presente trabalho avaliou o caldo de cana energia obtido de dois clones Tipo I como substrato para a produção de etanol, com base na determinação das suas características microbiológicas e deterioração ao longo do tempo, em comparação com o caldo de cana-de-açúcar (variedade RB867515). Foi observada uma clara diferenciação quanto ao crescimento bacteriano e de leveduras nas amostras de caldo analisadas, sendo o crescimento mais rápido no caldo de cana energia que no caldo de cana-de-açúcar. A manutenção do caldo por 8 horas a 30oC não causou impacto sobre a fermentação etanólica para quaisquer das amostras analisadas, apesar do crescimento significativo de bactérias. Houve um decréscimo de aproximadamente sete pontos percentuais na eficiência da fermentação com caldo de cana energia em um ciclo fermentativo de 24 horas com a levedura da panificação, em relação ao caldo da cana-de-açúcar. Apesar de a deterioração do caldo da cana energia ter sido mais rápida que a apresentada pelo caldo de cana-de-açúcar, o presente trabalho demonstrou que o caldo de cana energia tem potencial para ser utilizado como substrato nas indústrias produtoras de etanol. Do que se tem conhecimento, esse é o primeiro trabalho que trata das características de deterioração e fermentabilidade do caldo de cana energia.

Characteristics of Saccharomyces cerevisiae yeasts exhibiting rough colonies and pseudohyphal morphology with respect to alcoholic fermentation

Among the native yeasts found in alcoholic fermentation, rough colonies associated with pseudohyphal morphology belonging to the species Saccharomyces cerevisiae are very common and undesirable during the process. The aim of this work was to perform morphological and physiological characterisations of S. cerevisiae strains that exhibited rough and smooth colonies in an attempt to identify alternatives that could contribute to the management of rough colony yeasts in alcoholic fermentation. Characterisation tests for invasiveness in Agar medium, killer activity, flocculation and fermentative capacity were performed on 22 strains (11 rough and 11 smooth colonies). The effects of acid treatment at different pH values on the growth of two strains ("52" -rough and "PE-02" smooth) as well as batch fermentation tests with cell recycling and acid treatment of the cells were also evaluated. Invasiveness in YPD Agar medium occurred at low frequency; ten of eleven rough yeasts exhibited flocculation; none of the strains showed killer activity; and the rough strains presented lower and slower fermentative capacities compared to the smooth strains in a 48-h cycle in a batch system with sugar cane juice. The growth of the rough strain was severely affected by the acid treatment at pH values of 1.0 and 1.5; however, the growth of the smooth strain was not affected. The fermentative efficiency in mixed fermentation (smooth and rough strains in the same cell mass proportion) did not differ from the efficiency obtained with the smooth strain alone, most likely because the acid treatment was conducted at pH 1.5 in a batch cell-recycle test. A fermentative efficiency as low as 60% was observed with the rough colony alone.