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.

The yeasts are microorganisms with great potential for biotechnological applications in diverse areas. The biological control of phytopathogens by yeasts has showed satisfactory results under laboratory conditions, and it has already produced commercial formulations. With this as focus, this work aims to perform in vitro and in vivo evaluations of the action of a Torulaspora globosa yeast strain (1S112), isolated from sugarcane rhizosphere, against the phytopathogenic mold Colletotrichum sublineolum, the causative agent of anthracnose in sorghum. In vitro experiments included the antagonism test in Petri dishes with morphological hyphal evaluation; yeast killer activity; siderophore, volatile compound and hydrolytic enzyme production. In vivo experiments were conducted in greenhouse conditions with a sorghum variety susceptible to C. sublineolum by evaluating the anthracnose disease for 6 weeks. The results indicated that the yeast strain significantly controlled the fungal growth, either in vitro or in vivo. The strain of T. globosa exhibited killer activity against two sensitive strains, which is a novel capacity for this species. The yeast did not produce siderophores, volatile compounds or hydrolytic enzymes, although it has reduced the mycelial growth, resulting in hyphal deformities but not cell death. The yeast controlled the anthracnose disease in sorghum, either inoculated before or after the fungal spores, suggesting that the competition for space and nutrients to dominate the mold and killer toxin production, altering the hyphal morphology, are mechanisms utilized by the yeast in the biocontrol.

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.

The search for new microbial strains that are able to withstand inhibitors released from hemicellulosic hydrolysis and are also still able to convert sugars in ethanol/xylitol is highly desirable. A yeast strain isolated from sugarcane juice and identified as Meyerozyma guilliermondii was evaluated for the ability to grow and ferment pentoses in synthetic media and in sugarcane bagasse hydrolysate. The yeast grew in xylose, arabinose and glucose at the same rate at an initial medium pH of 5.5. At pH 4.5, the yeast grew more slowly in arabinose. There was no sugar exhaustion within 60 h. At higher xylose concentrations with a higher initial cell concentration, sugar was exhausted within 96 h at pH 4.5. An increase of 350 % in biomass was obtained in detoxified hydrolysates, whereas supplementation with 3 g/L yeast extract increased biomass production by approximately 40 %. Ethanol and xylitol were produced more significantly in supplemented hydrolysates regardless of detoxification. Xylose consumption was enhanced in supplemented hydrolysates and arabinose was consumed only when xylose and glucose were no longer available. Supplementation had a greater impact on ethanol yield and productivity than detoxification; however, the product yields obtained in the present study are still much lower when compared to other yeast species in bagasse hydrolysate. By the other hand, the fermentation of both xylose and arabinose and capability of withstanding inhibitors are important characteristics of the strain assayed.

The fungus Aspergillus niger was cultivated in culture medium with an alkaline ultramafic rock powder to evaluate the solubilization of potassium for biofertilizer production. The assays were carried out with 2 strains (CCT4355 and CCT911) in small-scale batch fermentations using 125, 500, 1000, and 2000 mL Erlenmeyer flasks, with a nominal volume of 40%, and rock powder at 0.4%, shaken at 160 r/min, incubated at 30 degrees C, and sampled every 7 days for 35 days. The amount of soluble K(+), the pH of the culture medium, and the acidity were determined. Both strains solubilized K(+) from the rock powder to the same extent (approximately 62%-70% after 35 days) in the 125 mL flasks; however, the percent solubilization decreased at higher volumetric scales. The results also indicated a difference in strain sensitivity to the increase in volumetric scales in batch fermentation. When filter-sterilized air was injected into the medium, the K(+) percent solubilization obtained after 4 days of cultivation was similar to that obtained after a 28 day period. The acid production by the fungus may be a mechanism of rock solubilization, in spite of the elevation in pH values probably caused by the increasing hydrolysis of the silicates. Both strains of A. niger are recommended for solubilizing potassium from ultramafic rocks, but it is necessary to optimize the oxygen transfer, which seemed to affect the rock solubilization at higher volumetric scales.

The ethanol production in Brazil is carried out by fed-batch or continuous process with cell recycle, in such way that bacterial contaminants are also recycled and may be troublesome due to the substrate competition. Addition of sulphuric acid when inoculum cells are washed can control the bacterial growth or alternatively biocides are used. This work aimed to verify the effect of chlorine dioxide, a well-known biocide for bacterial decontamination of water and equipments, against contaminant bacteria (Bacillus subtilis, Lactobacillus plantarum, Lactobacillus fermentum and Leuconostoc mesenteroides) from alcoholic fermentation, through the method of minimum inhibitory concentration (MIC), as well as its effect on the industrial yeast inoculum. Lower MIC was found for B. subtilis (10 ppm) and Leuconostoc mesenteroides (50 ppm) than for Lactobacillus fermentum (75 ppm) and Lactobacillus plantarum (125 ppm). Additionally, these concentrations of chlorine dioxide had similar effects on bacteria as 3 ppm of Kamoran® (recommended dosage for fermentation tanks), exception for B. subtilis, which could not be controlled at this Kamoran® dosage. The growth of industrial yeasts was affected when the concentration of chlorine dioxide was higher than 50 ppm, but the effect was slightly dependent on the type of yeast strain. Smooth yeast colonies (dispersed cells) seemed to be more sensitive than wrinkled yeast colonies (clustered cells/pseudohyphal growth), both isolated from an alcoholproducing unit during the 2006/2007 sugar cane harvest. The main advantage in the usage of chlorine dioxide that it can replace antibiotics, avoiding the selection of resistant populations of microorganisms.

Fungal dimorphism is a complex phenomenon triggered by a large variety of environmental factors and consists of a reversible alternating pattern of growth between different elliptical and filamentous forms of cells. Understanding the mechanisms that regulate these events is of major interest because of their implications in fungal pathogenesis, cell differentiation and industry. Diploid cells of Saccharomyces cerevisiae transform from budding yeast to pseudohyphae when starved for nitrogen, giving the cells an advantage in food foraging, which is sensed by at least two signal transduction pathways: the MAP kinase (MAPK) and the PKA (cAMP-dependent protein kinase A) pathways. The output of these signalling pathways is the expression of pseudohypha-specific genes, whose expression profiles change and is accompanied by a G2 delay in the cell cycle and a prolonged period of polarized growth. Haploid yeast strains show a similar growth type after prolonged incubation on rich medium plates. The cells form chains and invade the agar on the edge of the colony, but they do not become elongated. This growth type is referred to as haploid invasive growth. Alcohols can also induce filamentous growth in S. cerevisiae, promoting aberrant and elongated morphology. The three forms of filamentous growth are revised in this article and also the pathways involved in sensing, signaling and signal transduction during filamentous growth.

Agro-industrial wastes are of great interest because they are important natural sources of bioactive compounds and can generate value-added byproducts. Recent studies have shown that byproducts generated by the food processing industry are rich in bioactive compounds, such as phenolic compounds, organic acids, and carotenoids, among others. The growing interest in replacing synthetic antioxidant and antimicrobial compounds with natural ones has stimulated a search for these bioactive compounds from plant sources, especially from fruit-processing wastes. The study aims to project the agro-industrial wastes as potential natural sources of antioxidants and antimicrobials and the feasible technological applications in food and fermentation industries, especially the bioethanol industry.