Ethanol tolerance of thermotolerant yeasts cultivated on mixtures of sucrose and ethanol

The final levels of ethanol (levels of ethanol produced plus that added initially to the media) reached by the thermotolerant yeasts were highest (16.5-20.3%, v/v) at 8% initial ethanol. The thermotolerant yeasts were found to have the following characteristics: constant levels of ethanol formation (10.5-12.3%, v/v), fog additions of external ethanol within the range 2-8% (v/v) of initial ethanol; constant values of product coefficients when initial ethanol was in the range of 2-6%, which increased or decreased, depending on the strain, when initial ethanol exceeded 6%; growth activity was inhibited at different levels of addition of external ethanol when final biomass and specific rate of growth were compared; significant differences among the yeast strains in the amount of external ethanol capable of reducing biomass formation by one half. In addition, the viability of the strains (early stationary phase) varied with the amount of external ethanol, the lowest viabilities occurring at concentrations of initial ethanol ranging from 4 to 7% and the highest in the range of 7 to 8% (v/v). The relative levels of trehalose (with/without 7% ethanol added initially) in the yeast strains (the stationary phase) ranged from 1.03 to 1.75, suggesting that the effect of produced ethanol on trehalose accumulation was stronger than that of external ethanol. The levels of final ethanol shown by the yeast strains were also correlated with the cellular levels of glycerol-3-phosphate dehydrogenase (increase in enzyme levels with decrease in final ethanol) for cells harvested at the stationary phase.

Partitioning of the glucoamylase activity at the cell surfaces in cultures of Saccharomyces

Glucoamylases have been used with alpha-amylases for the industrial conversion of starch into glucose. However, little is known about the properties of this glycosylated protein retained in the cell wall of Saccharomyces as well as its role in the saccharification and fermentation of amylaceous substrates, notably in high cell density processes. In most of the strains assayed, decreases in biomass formation were followed by increases in glucoamylase secretion (expressed as U/mg(biomass) in 1 ml of culture) when glucose was exchanged for starch as carbon source or the growth temperature was raised from 30 to 35 degrees C. Despite the losses in viability, significant increases in the activity of the wall fraction occurred when cultures of thermotolerant yeasts propagated at 30 degrees C or washed cells resuspended in buffer solution were heated to 60 degrees C for 60-80 min prior to amylolytic assays. Thus, intact cells of thermotolerant yeasts can be used as colloidal biocatalysts in starch degradation processes. (C) 2005 Published by Elsevier Ltd.

Biosurfactants production by yeasts using soybean oil and glycerol as low cost substrate

Biosurfactants are bioactive agents that can be produced by many different microorganisms. Among those, special attention is given to yeasts, since they can produce many types of biosurfactants in large scale, using several kinds of substrates, justifying its use for industrial production of those products. For this production to be economically viable, the use of residual carbon sources is recommended. The present study isolated yeasts from soil contaminated with petroleum oil hydrocarbons and assessed their capacity for producing biosurfactants in low cost substrates. From a microbial consortium enriched, seven yeasts were isolated, all showing potential for producing biosurfactants in soybean oil. The isolate LBPF 3, characterized as Candida antarctica, obtained the highest levels of production - with a final production of 13.86 g/L. The isolate LBPF 9, using glycerol carbon source, obtained the highest reduction in surface tension in the growth medium: approximately 43% of reduction after 24 hours of incubation. The products obtained by the isolates presented surfactant activity, which reduced water surface tension to values that varied from 34 mN/m, obtained from the product of isolates LBPF 3 and 16 LBPF 7 (respectively characterized as Candida antarctica and Candida albicans) to 43 mN/m from the isolate LPPF 9, using glycerol as substrate. The assessed isolates all showed potential for the production of biosurfactants in conventional sources of carbon as well as in agroindustrial residue, especially in glycerol.

Yeasts isolated from a fungus-growing ant nest, including the description of Trichosporon chiarellii sp nov., an anamorphic basidiomycetous yeast

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Occurrence of yeasts, pseudomonads and enteric bacteria in the oral cavity of patients undergoing head and neck radiotherapy

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Occurrence of yeasts, enterococci and other enteric bacteria in subgingival biofilm of HIV-positive patients with chronic gingivitis and necrotizing periodontitis

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Genomic DNA microarray comparison of gene expression patterns in Paracoccidioides brasiliensis mycelia and yeasts in vitro

Paracoccidioides brasiliensis is a thermally dimorphic fungus, and causes the most prevalent systemic mycosis in Latin America. Infection is initiated by inhalation of conidia or mycelial fragments by the host, followed by further differentiation into the yeast form. Information regarding gene expression by either form has rarely been addressed with respect to multiple time points of growth in culture. Here, we report on the construction of a genomic DNA microarray, covering approximately 25% of the genome of the organism, and its utilization in identifying genes and gene expression patterns during growth in vitro. Cloned, amplified inserts from randomly sheared genomic DNA (gDNA) and known control genes were printed onto glass slides to generate a microarray of over 12 000 elements. To examine gene expression, mRNA was extracted and amplified from mycelial or yeast cultures grown in semi-defined medium for 5, 8 and 14 days. Principal components analysis and hierarchical clustering indicated that yeast gene expression profiles differed greatly from those of mycelia, especially at earlier time points, and that mycelial gene expression changed less than gene expression in yeasts over time. Genes upregulated in yeasts were found to encode proteins shown to be involved in methionine/cysteine metabolism, respiratory and metabolic processes (of sugars, amino acids, proteins and lipids), transporters (small peptides, sugars, ions and toxins), regulatory proteins and transcription factors. Mycelial genes involved in processes such as cell division, protein catabolism, nucleotide biosynthesis and toxin and sugar transport showed differential expression. Sequenced clones were compared with Histoplasma capsulatum and Coccidioides posadasii genome sequences to assess potentially common pathways across species, such as sulfur and lipid metabolism, amino acid transporters, transcription factors and genes possibly related to virulence. We also analysed gene expression with time in culture and found that while transposable elements and components of respiratory pathways tended to increase in expression with time, genes encoding ribosomal structural proteins and protein catabolism tended to sharply decrease in expression over time, particularly in yeast. These findings expand our knowledge of the different morphological forms of P. brasiliensis during growth in culture.

A synthetic peptide selectively kills only virulent Paracoccidioides brasiliensis yeasts

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Candida heliconiae sp nov., Candida picinguabensis sp nov and Candida saopaulonensis sp nov., three ascomycetous yeasts from Heliconia velloziana (Heliconiaceae)

Strains belonging to three novel yeast species, Candida heliconiae (four isolates), Candida picinguabensis (three isolates) and Candida saopaulonensis (two isolates), were recovered in the year 2000 from water of flower bracts of Heliconia velloziana L. Emigd. (Heliconiaceae) found in a forest ecosystem site in an Atlantic rainforest of south-eastern Brazil. C. picinguabensis and C. saopaulonensis were nearly identical in morphology and physiology, but sequence divergence in the D1/D2 domain of the large-subunit rDNA indicated that they should be regarded as different species. They belong to the Metschnikowiaceae clade. C. heliconiae had affinities to Pichia mexicana and related species, but was genetically isolated from all currently accepted species in that group. The type strains are C. heliconiae UNESP 00-91 C1(T) (= CBS 10000(T) = NRRL Y-27813(T)), C. picinguabensis UNESP 00-89(T) (= CBS 9999(T) = NRRL Y-27814(T)) and C. saopaulonensis UNESP 00-99(T) (=CBS 10001(T) = NRRL Y-27815(T)).

Antagonistic interactions between garden yeasts and microfungal garden pathogens of leaf-cutting ants

We investigate the diversity of yeasts isolated in gardens of the leafcutter ant Atta texana. Repeated sampling of gardens from four nests over a 1-year time period showed that gardens contain a diverse assemblage of yeasts. The yeast community in gardens consisted mostly of yeasts associated with plants or soil, but community composition changed between sampling periods. In order to understand the potential disease-suppressing roles of the garden yeasts, we screened isolates for antagonistic effects against known microfungal garden contaminants. In vitro assays revealed that yeasts inhibited the mycelial growth of two strains of Escovopsis (a specialized attine garden parasite), Syncephalastrum racemosum (a fungus often growing in gardens of leafcutter lab nests), and the insect pathogen Beauveria bassiana. These garden yeasts add to the growing list of disease-suppressing microbes in attine nests that may contribute synergistically, together with actinomycetes and Burkholderia bacteria, to protect the gardens and the ants against diseases. Additionally, we suggest that garden immunity against problem fungi may therefore derive not only from the presence of disease-suppressing Pseudonocardia actinomycetes, but from an enrichment of multiple disease-suppressing microorganisms in the garden matrix.

Yeasts and filamentous fungi carried by the gynes of leaf-cutting ants

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Generation of Nutrients and Detoxification: Possible Roles of Yeasts in Leaf-Cutting Ant Nests.

The possible roles played by yeasts in attine ant nests are mostly unknown. Here we present our investigations on the plant polysaccharide degradation profile of 82 yeasts isolated from fungus gardens of Atta and Acromyrmex species to demonstrate that yeasts found in ant nests may play the role of making nutrients readily available throughout the garden and detoxification of compounds that may be deleterious to the ants and their fungal cultivar. Among the yeasts screened, 65% exhibited cellulolytic enzymes, 44% exhibited pectinolytic activity while 27% and 17% possess enzyme systems for the degradation of protease and amylase, respectively. Galacturonic acid, which had been reported in previous work to be poorly assimilated by the ant fungus and also to have a negative effect on ants' survival, was assimilated by 64% and 79% of yeasts isolated from nests of A. texana and Acromyrmex respectively. Our results suggest that yeasts found in ant nests may participate in generation of nutrients and removal of potentially toxic compounds, thereby contributing to the stability of the complex microbiota found in the leaf-cutting ant nests.

Selection of thermophilic and thermotolerant fungi for the production of cellulases and xylanases under solid-state fermentation

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Isolation and molecular identification of wine yeasts from a Brazilian vineyard

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Production and partial characterization of polygalacturonases produced by thermophilic Monascus sp N8 and by thermotolerant Aspergillus sp N12 on solid-state fermentation

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)