The physiological characteristics of the yeast Dekkera bruxellensis in fully fermentative conditions with cell recycling and in mixed cultures with Saccharomyces cerevisiae.

The yeast Dekkera bruxellensis plays an important role in industrial fermentation processes, either as a contaminant or as a fermenting yeast. In this study, an analysis has been conducted of the fermentation characteristics of several industrial D. bruxellensis strains collected from distilleries from the Southeast and Northeast of Brazil, compared with Saccharomyces cerevisiae. It was found that all the strains of D. bruxellensis showed a lower fermentative capacity as a result of inefficient sugar assimilation, especially sucrose, under anaerobiosis, which is called the Custer effect. In addition, most of the sugar consumed by D. bruxellensis seemed to be used for biomass production, as was observed by the increase of its cell population during the fermentation recycles. In mixed populations, the surplus of D. bruxellensis over S. cerevisiae population could not be attributed to organic acid production by the first yeast, as previously suggested. Moreover, both yeast species showed similar sensitivity to lactic and acetic acids and were equally resistant to ethanol, when added exogenously to the fermentation medium. Thus, the effects that lead to the employment of D. bruxellensis in an industrial process and its effects on the production of ethanol are multivariate. The difficulty of using this yeast for ethanol production is that it requires the elimination of the Custer effect to allow an increase in the assimilation of sugar under anaerobic conditions.

Lachancea mirantina sp. nov., an ascomycetous yeast isolated from the cachaca fermentation process.

In the present work, a novel ascomycete species, Lachancea mirantina sp. nov., isolated from the fermentation process that produces cachaça, a Brazilian spirit, is proposed. Nucleotide sequence analysis of the 26S D1/D2 rDNA locus showed that L. mirantina sp. nov. was genetically related to Lachancea cidri and Lachancea fermentati, although some physiological traits showed remarkable differences. Analysis of the D1/D2 large-subunit rDNA molecular marker showed a clear distinction among all three species, confirming that L. mirantina sp. nov. belongs to a separate taxonomic species in the Lachancea clade. The type strain of Lachancea mirantina sp. nov. is URM 5925(T) ( = CLIB 1160(T)  = CBS 11717(T)).

Yeast species involved in artisanal cachaça fermentation in three stills with different technological levels in Pernambuco, Brazil.

Both the taste and aroma of cachaça, an alcoholic beverage produced by yeast fermentation of sugar cane, are influenced by yeast metabolites and volatiles. The knowledge of yeast population dynamics during the fermentation process will help to establish the basis for quality control of alcoholic beverage. In the present work, the population dynamics of three fermentation processes, with differing levels of technological sophistication, were studied. Saccharomyces cerevisiae was found to be the dominant species, but Candida milleri (Candida humilis), Pichia caribbica, Pichia guilliermondii and Zygosaccharomyces fermentati (Lachancea fermentati) were also significantly involved. In addition, four new yeast species that are not represented in NCBI/EMBL nucleotide database were found. These yeasts were classified as Candida sp., Candida drosophilae-like, Candida ubatubensis-like and Zygosaccharomyces sp. In fermentation trails at laboratory scale, all species were found to contribute to the production of volatiles. Thus it is probable that product quality is strongly dependent on population dynamics during the fermentation process.

Genetic variability within Fusarium solani specie as revealed by PCR-fingerprinting based on pcr markers

O fungo Fusarium solani (teleomorfo Haematonectria haematococca) apresenta uma expressiva importância na agricultura por ser considerado patógeno para várias culturas de interesse econômico causando doença conhecida por podridão das raízes, além de ser patógeno aos animais e ao homem, provocando nestes últimos, micoses superficiais e sistêmicas. A complexidade associada a sua identificação correta através de métodos tradicionais justifica os esforços de usar marcadores moleculares para caracterização dos isolados. Neste trabalho, três métodos baseados na tecnologia da PCR (um por ribotipagem por PCR e dois por impressão genética por PCR) foram utilizados para investigar a variabilidade molecular de dezoito isolados de F. solani de quatro Estados brasileiros, coletados de diferentes substratos. A análise genética revelou a variabilidade intraespecífica dos isolados de F. solani, sem qualquer correlação para a origem geográfica e substrato. Seu polimorfismo foi observado até mesmo na seqüência conservada do locus do rDNA, e o marcador SPAR (GTG)5 mostrou o mais alto polimorfismo. Em conjunto, estes resultados poderão auxiliar nos estudos da relação entre variabilidade do perfil genético de isolados e os fenótipos de resistência de determinados cultivares às doenças provocadas pelo fungo, orientando programas de melhoramento vegetal.