Inhibitor tolerance and flocculation of a yeast strain suitable for second generation bioethanol production

Background: Robust second generation bioethanol processes require microorganisms able to ferment inhibitory lignocellullosic hydrolysates. In this study, the inhibitor tolerance and flocculation characteristics of Saccharomyces cerevisiae CCUG53310 were evaluated in comparison with S. cerevisiae CBS8066. Results: The flocculating strain CCUG53310 could rapidly ferment all hexoses in dilute acid spruce hydrolysate, while CBS8066 was strongly inhibited in this medium. In synthetic inhibitory media, CCUG53310 was more tolerant to carboxylic acids and furan aldehydes, but more sensitive than CBS8066 to phenolic compounds. Despite the higher tolerance, the increase in expression of the YAP1, ATR1 and FLR1 genes, known to confer resistance to lignocellulose-derived inhibitors, was generally smaller in CCUG53310 than in CBS8066 in inhibitory media. The flocculation of CCUG53310 was linked to the expression of FLO8, FLO10 and one or more of FLO1, FLO5 or FLO9. Flocculation depended on cell wall proteins and Ca2+ ions, but was almost unaffected by other compounds and pH values typical for lignocellulosic media. Conclusions: S. cerevisiae CCUG53310 can be characterised as being very robust, with great potential for industrial fermentation of lignocellulosic hydrolysates relatively low in phenolic inhibitors.

Assessment of the antifungal activity of Spirulina platensis phenolic extract against Aspergillus flavus / Avaliação da atividade antifúngica de extrato fenólico de Spirulina platensis contra Aspergillus flavus

The production of safe food has stimulated the search for natural substances that possess antifungal activity. The indirect methods of estimating fungal biomass are based on the measurement of glucosamine, ergosterol and protein - typical compounds produced during the development of biomass. The aim of the study was to assess the effect of the phenolic extract from Spirulina platensis on the production of structural compounds in Aspergillus flavus, in order to identify its action on fungal inhibition. The Spirulina platensis methanolic extracts presented 1.15 mg phenolic compound/g Spirulina platensis, which showed an antifungal effect against Aspergillus flavus, inhibiting the glucosamine production up to 56 percent. Therefore, it may be employed as natural defense when food protection is necessary.

A produção de alimentos seguros tem estimulado a busca por substâncias naturais que possuem atividade antifúngica. Os métodos indiretos de estimativa de biomassa fúngica são baseados na medição de glucosamina, ergosterol e proteína - compostos típicos produzidos durante o desenvolvimento da biomassa. Neste estudo, objetivou-se avaliar o efeito do extrato fenólico de Spirulina platensis na produção de componentes estruturais em Aspergillus flavus, a fim de identificar seu mecanismo de ação dos fenóis na inibição fúngica. O extrato metanólico de Spirulina platensis apresentou 1,15 mg de compostos fenólicos/g Spirulina platensis, apresentando um efeito antifúngico contra Aspergillus flavus, inibindo a produção de glucosamina em até 56 por cento. Portanto, pode ser empregado como antifúngico natural quando for necessária a proteção de alimentos.