Polyhydroxyalkanoate Production from Eucalyptus Bark's Enzymatic Hydrolysate.

In recent years, polyhydroxyalkanoates (PHAs) have gained notoriety because of their desirable properties that include proven biodegradability, biocompatibility, and thermal stability, which make them suitable alternatives to fossil-based polymers. However, the widespread use of PHAs is still challenging because of their production costs, which are greatly associated with the cultivation medium used for bacterial cultivation. In Portugal, one-quarter of the forest area is covered by Eucalyptus globulus wood, making its residues a cheap, abundant, and sustainable potential carbon source for biotechnological uses. In this work, eucalyptus bark was used as the sole feedstock for PHA production in a circular bioeconomic approach. Eucalyptus bark hydrolysate was obtained after enzymatic saccharification using Cellic® CTec3, resulting in a sugar-rich solution containing glucose and xylose. Although with differing performances, several bacteria were able to grow and produce PHA with distinct compositions, using the enzymatic hydrolysate as the sole carbon source. Pseudomonas citronellolis NRRL B-2504 achieved a high cellular growth rate in bioreactor assays (24.4 ± 0.15 g/L) but presented a low accumulation of a medium-chain-length PHA (mcl-PHA) comprising the monomers hydroxydecanoate (HD, 65%), hydroxydodecanoate (HDd, 25%), and hydroxytetradecanoate (HTd, 14%). Burkholderia thailandensis E264, on the other hand, reached a lower cellular growth rate (8.87 ± 0.34 g/L) but showed a higher biopolymer accumulation, with a polyhydroxybutyrate (PHB) content in the cells of 12.3 wt.%. The new isolate, Pseudomonas sp., revealed that under nitrogen availability, it was able to reach a higher accumulation of the homopolymer PHB (31 wt.%). These results, although preliminary, demonstrate the suitability of eucalyptus bark's enzymatic hydrolysate as a feedstock for PHA production, thus offering an exciting avenue for achieving sustainable and environmentally responsible plastic products from an undervalued forestry waste.

Visible light-exposed lignin facilitates cellulose solubilization by lytic polysaccharide monooxygenases.

Lytic polysaccharide monooxygenases (LPMOs) catalyze oxidative cleavage of crystalline polysaccharides such as cellulose and are crucial for the conversion of plant biomass in Nature and in industrial applications. Sunlight promotes microbial conversion of plant litter; this effect has been attributed to photochemical degradation of lignin, a major redox-active component of secondary plant cell walls that limits enzyme access to the cell wall carbohydrates. Here, we show that exposing lignin to visible light facilitates cellulose solubilization by promoting formation of H2O2 that fuels LPMO catalysis. Light-driven H2O2 formation is accompanied by oxidation of ring-conjugated olefins in the lignin, while LPMO-catalyzed oxidation of phenolic hydroxyls leads to the required priming reduction of the enzyme. The discovery that light-driven abiotic reactions in Nature can fuel H2O2-dependent redox enzymes involved in deconstructing lignocellulose may offer opportunities for bioprocessing and provides an enzymatic explanation for the known effect of visible light on biomass conversion.

Imidazole Processing of Wheat Straw and Eucalyptus Residues-Comparison of Pre-Treatment Conditions and Their Influence on Enzymatic Hydrolysis.

Biomass pre-treatment is a key step in achieving the economic competitiveness of biomass conversion. In the present work, an imidazole pre-treatment process was performed and evaluated using wheat straw and eucalyptus residues as model feedstocks for agriculture and forest-origin biomasses, respectively. Results showed that imidazole is an efficient pre-treatment agent; however, better results were obtained for wheat straw due to the recalcitrant behavior of eucalyptus residues. The temperature had a stronger effect than time on wheat straw pre-treatment but at 160 °C and 4 h, similar results were obtained for cellulose and hemicellulose content from both biomasses (ca. 54% and 24%, respectively). Lignin content in the pre-treated solid was higher for eucalyptus residues (16% vs. 4%), as expected. Enzymatic hydrolysis, applied to both biomasses after different pre-treatments, revealed that results improved with increasing temperature/time for wheat straw. However, these conditions had no influence on the results for eucalyptus residues, with very low glucan to glucose enzymatic hydrolysis yield (93% for wheat straw vs. 40% for eucalyptus residues). Imidazole can therefore be considered as a suitable solvent for herbaceous biomass pre-treatment.

The use of flow cytometry to assess Rhodosporidium toruloides NCYC 921 performance for lipid production using Miscanthus sp. hydrolysates.

The yeast Rhodosporidium toruloides NCYC 921 was used for lipid production, using Miscanthus biomass hydrolysate as carbon source. The hydrolysate was obtained by enzymatic hydrolysis of Miscanthus biomass (at high solids loading) previously subjected to a hydrothermal pre-treatment. Afterwards R. toruloides was grown on Miscanthus sp. hydrolysate (MH), undiluted and diluted, at the ratios of 1:4 (20 % v/v), 1:2 (33.3 % v/v) and 3:1 (75 % v/v). The best yeast performance was observed for MH 1:2 medium dilution, reaching the maximal biomass concentration of 6.3 g/L, the lipid content of 30.67 % w/w dry cell weight and the lipid concentration of 1.64 g/L. Flow cytometry demonstrated that R. toruloides cell membrane was massively damaged when the yeast was grown on undiluted MH, due to the presence of phenolic compounds; however, when the yeast was grown on diluted MH 1:2 and 1:4, the proportion of intact cells has increased during the yeast cultivation.

A Thermotolerant Xylan-Degrading Enzyme Is Produced by Streptomyces malaysiensis AMT-3 Using by-Products From the Food Industry

Abstract This study evaluated the production of endoxylanases by Streptomyces malaysiensis AMT-3 in submerged fermentation using by-products of the food industry at 28ºC. In shake-flasks experiments, the highest endoxylanase activity of 45.8 U.mL-1 was observed within 6 days in a medium containing (w/v) 2.5% wheat bran and 1.2% corn steep liquor. The same culture conditions were used to evaluate the enzyme production in a 2 L stirred tank reactor under different agitation (300, 450 and 600 rev.min-1) and aeration (30 and 60 L.h-1) conditions. The use of 450 rev.min-1 coupled to an aeration of 90 L.h-1 resulted on 81.3 U.mL-1 endoxylanase activity within 5 days. The effect of temperature and pH on endoxylanase activity and stability showed the highest activity at 60 ºC and pH 6.0. Zymography showed the presence of three xylanolytic bands with molecular masses of 690, 180 and 142 kDa. The results showed that the thermotolerant actinobacterial endoxylanase can be produced in high titers using by-product of the food industry.

The Effect of the Chemical Character of Ionic Liquids on Biomass Pre-Treatment and Posterior Enzymatic Hydrolysis.

Ionic liquids have been recognised as interesting solvents applicable in efficient lignocellulosic biomass valorisation, especially in biomass fractionation into individual polymeric components or direct hydrolysis of some biomass fractions. Considering the chemical character of ionic liquids, two different approaches paved the way for the fractionation of biomass. The first strategy integrated a pre-treatment, hydrolysis and conversion of biomass through the employment of hydrogen-bond acidic 1-ethyl-3-methyimidazolim hydrogen sulphate ionic liquid. The second strategy relied on the use of a three-step fractionation process with hydrogen-bond basic 1-ethyl-3-methylimidazolium acetate to produce high purity cellulose, hemicellulose and lignin fractions. The proposed approaches were scrutinised for wheat straw and eucalyptus residues. These different biomasses enabled an understanding that enzymatic hydrolysis yields are dependent on the crystallinity of the pre-treated biomass. The use of acetate based ionic liquid allowed crystalline cellulose I to change to cellulose II and consequently enhanced the glucan to glucose yield to 93.1 ± 4.1 mol% and 82.9 ± 1.2 mol% for wheat straw and eucalyptus, respectively. However, for hydrogen sulphate ionic liquid, the same enzymatic hydrolysis yields were 61.6 ± 0.2 mol% for wheat straw and only 7.9 ± 0.3 mol% for eucalyptus residues. These results demonstrate the importance of both ionic liquid character and biomass type for efficient biomass processing.

Evaluation of the ethanol tolerance for wild and mutant Synechocystis strains by flow cytometry.

Flow cytometry was used to evaluate the effect of initial ethanol concentrations on cyanobacterial strains of Synechocystis PCC 6803 [wild-type (WT), and ethanol producing recombinants (UL 004 and UL 030)] in batch cultures. Ethanol recombinants, containing one or two metabolically engineered cassettes, were designed towards the development of an economically competitive process for the direct production of bioethanol from microalgae through an exclusive autotrophic route. It can be concluded that the recombinant Synechocystis UL 030 containing two copies of the genes per genome was the most tolerant to ethanol. Nevertheless, to implement a production process using recombinant strains, the bioethanol produced will be required to be continuously extracted from the culture media via a membrane-based technological process for example to prevent detrimental effects on the biomass. The results presented here are of significance in defining the maximum threshold for bulk ethanol concentration in production media.

Exploring xylose metabolism in Spathaspora species: XYL1.2 from Spathaspora passalidarum as the key for efficient anaerobic xylose fermentation in metabolic engineered Saccharomyces cerevisiae.

BACKGROUND: The production of ethanol and other fuels and chemicals from lignocellulosic materials is dependent of efficient xylose conversion. Xylose fermentation capacity in yeasts is usually linked to xylose reductase (XR) accepting NADH as cofactor. The XR from Scheffersomyces stipitis, which is able to use NADH as cofactor but still prefers NADPH, has been used to generate recombinant xylose-fermenting Saccharomyces cerevisiae. Novel xylose-fermenting yeasts species, as those from the Spathaspora clade, have been described and are potential sources of novel genes to improve xylose fermentation in S. cerevisiae. RESULTS: Xylose fermentation by six strains from different Spathaspora species isolated in Brazil, plus the Sp. passalidarum type strain (CBS 10155(T)), was characterized under two oxygen-limited conditions. The best xylose-fermenting strains belong to the Sp. passalidarum species, and their highest ethanol titers, yields, and productivities were correlated to higher XR activity with NADH than with NADPH. Among the different Spathaspora species, Sp. passalidarum appears to be the sole harboring two XYL1 genes: XYL1.1, similar to the XYL1 found in other Spathaspora and yeast species and XYL1.2, with relatively higher expression level. XYL1.1p and XYL1.2p from Sp. passalidarum were expressed in S. cerevisiae TMB 3044 and XYL1.1p was confirmed to be strictly NADPH-dependent, while XYL1.2p to use both NADPH and NADH, with higher activity with the later. Recombinant S. cerevisiae strains expressing XYL1.1p did not show anaerobic growth in xylose medium. Under anaerobic xylose fermentation, S. cerevisiae TMB 3504, which expresses XYL1.2p from Sp. passalidarum, revealed significant higher ethanol yield and productivity than S. cerevisiae TMB 3422, which harbors XYL1p N272D from Sc. stipitis in the same isogenic background (0.40 vs 0.34 g gCDW (-1) and 0.33 vs 0.18 g gCDW (-1) h(-1), respectively). CONCLUSION: This work explored a new clade of xylose-fermenting yeasts (Spathaspora species) towards the engineering of S. cerevisiae for improved xylose fermentation. The new S. cerevisiae TMB 3504 displays higher XR activity with NADH than with NADPH, with consequent improved ethanol yield and productivity and low xylitol production. This meaningful advance in anaerobic xylose fermentation by recombinant S. cerevisiae (using the XR/XDH pathway) paves the way for the development of novel industrial pentose-fermenting strains.

Life cycle assessment of advanced bioethanol production from pulp and paper sludge.

This work evaluates the environmental performance of using pulp and paper sludge as feedstock for the production of second generation ethanol. An ethanol plant for converting 5400 tons of dry sludge/year was modelled and evaluated using a cradle-to-gate life cycle assessment approach. The sludge is a burden for pulp and paper mills that is mainly disposed in landfilling. The studied system allows for the valorisation of the waste, which due to its high polysaccharide content is a valuable feedstock for bioethanol production. Eleven impact categories were analysed and the results showed that enzymatic hydrolysis and neutralisation of the CaCO3 are the environmental hotspots of the system contributing up to 85% to the overall impacts. Two optimisation scenarios were evaluated: (1) using a reduced HCl amount in the neutralisation stage and (2) co-fermentation of xylose and glucose, for maximal ethanol yield. Both scenarios displayed significant environmental impact improvements.

Biorefining strategy for maximal monosaccharide recovery from three different feedstocks: eucalyptus residues, wheat straw and olive tree pruning.

This work proposes the biorefining of eucalyptus residues (ER), wheat straw (WS) and olive tree pruning (OP) combining hydrothermal pretreatment (autohydrolysis) with acid post-hydrolysis of the liquid fraction and enzymatic hydrolysis of the solid fraction towards maximal recovery of monosaccharides from those lignocellulose materials. Autohydrolysis of ER, WS and OP was performed under non-isothermal conditions (195-230°C) and the non-cellulosic saccharides were recovered in the liquid fraction while cellulose and lignin remained in the solid fraction. The acid post-hydrolysis of the soluble oligosaccharides was studied by optimizing sulfuric acid concentration (1-4%w/w) and reaction time (10-60 min), employing a factorial (2(2)) experimental design. The solids resulting from pretreatment were submitted to enzymatic hydrolysis by applying commercial cellulolytic enzymes Celluclast® 1.5L and Novozyme® 188 (0.225 and 0.025 g/g solid, respectively). This strategy provides high total monosaccharide recovery or high glucose recovery from lignocellulosic materials, depending on the autohydrolysis conditions applied.

Hydrothermal pretreatment of several lignocellulosic mixtures containing wheat straw and two hardwood residues available in Southern Europe.

This work studied the processing of biomass mixtures containing three lignocellulosic materials largely available in Southern Europe, eucalyptus residues (ER), wheat straw (WS) and olive tree pruning (OP). The mixtures were chemically characterized, and their pretreatment, by autohydrolysis, evaluated within a severity factor (logR0) ranging from 1.73 up to 4.24. A simple modeling strategy was used to optimize the autohydrolysis conditions based on the chemical characterization of the liquid fraction. The solid fraction was characterized to quantify the polysaccharide and lignin content. The pretreatment conditions for maximal saccharides recovery in the liquid fraction were at a severity range (logR0) of 3.65-3.72, independently of the mixture tested, which suggests that autohydrolysis can effectively process mixtures of lignocellulosic materials for further biochemical conversion processes.

Identification and characterisation of xylanolytic yeasts isolated from decaying wood and sugarcane bagasse in Brazil.

In this study, yeasts associated with lignocellulosic materials in Brazil, including decaying wood and sugarcane bagasse, were isolated, and their ability to produce xylanolytic enzymes was investigated. A total of 358 yeast isolates were obtained, with 198 strains isolated from decaying wood and 160 strains isolated from decaying sugarcane bagasse samples. Seventy-five isolates possessed xylanase activity in solid medium and were identified as belonging to nine species: Candida intermedia, C. tropicalis, Meyerozyma guilliermondii, Scheffersomyces shehatae, Sugiyamaella smithiae, Cryptococcus diffluens, Cr. heveanensis, Cr. laurentii and Trichosporon mycotoxinivorans. Twenty-one isolates were further screened for total xylanase activity in liquid medium with xylan, and five xylanolytic yeasts were selected for further characterization, which included quantitative analysis of growth in xylan and xylose and xylanase and ß-D-xylosidase activities. The yeasts showing the highest growth rate and cell density in xylan, Cr. laurentii UFMG-HB-48, Su. smithiae UFMG-HM-80.1 and Sc. shehatae UFMG-HM-9.1a, were, simultaneously, those exhibiting higher xylanase activity. Xylan induced the highest level of (extracellular) xylanase activity in Cr. laurentii UFMG-HB-48 and the highest level of (intracellular, extracellular and membrane-associated) ß-D-xylosidase activity in Su. smithiae UFMG-HM-80.1. Also, significant ß-D-xylosidase levels were detected in xylan-induced cultures of Cr. laurentii UFMG-HB-48 and Sc. shehatae UFMG-HM-9.1a, mainly in extracellular and intracellular spaces, respectively. Under xylose induction, Cr. laurentii UFMG-HB-48 showed the highest intracellular ß-D-xylosidase activity among all the yeast tested. C. tropicalis UFMG-HB 93a showed its higher (intracellular) ß-D-xylosidase activity under xylose induction and higher at 30 °C than at 50 °C. This study revealed different xylanolytic abilities and strategies in yeasts to metabolise xylan and/or its hydrolysis products (xylo-oligosaccharides and xylose). Xylanolytic yeasts are able to secrete xylanolytic enzymes mainly when induced by xylan and present different strategies (intra- and/or extracellular hydrolysis) for the metabolism of xylo-oligosaccharides. Some of the unique xylanolytic traits identified here should be further explored for their applicability in specific biotechnological processes.

Use of interdelta polymorphisms of Saccharomyces cerevisiae strains to monitor population evolution during wine fermentation.

The industrial use of starter cultures containing a consortium of different strains from the same species is nowadays seen as a possible strategy to enhance the organoleptic complexity of wines. To assess the relative contribution of each strain to the final product it is essential to quantify population evolution during the wine fermentation process, which requires strain-specific methods to identify and differentiate each strain. In the present study, a molecular method based on analysis of the polymorphisms exhibited by the PCR-amplification of the delta regions of three Saccharomyces cerevisiae strains was developed. A set of three pairs of primers (delta1-delta2, delta12-delta2, delta12-delta21) was used for each strain, and analysis of the resulting polymorphism patterns showed that the delta12-delta2 primer pair exhibited the highest resolution and discriminatory power. Thus, this pair of primers was selected to monitor the population evolution of a laboratory-scale wine fermentation performed in synthetic grape juice that was inoculated with similar amounts of each strain. The results showed that all strains grew together during the exponential growth phase (2-3 days) and maintained high cell density values (10(6)-10(7) cfu ml(-1)) throughout the stationary growth phase without significantly changing their relative population proportion, thus indicating that each strain can influence the chemical composition and final flavor of wine, albeit at different levels. This study also showed that PCR-amplification of DNA delta sequences of S. cerevisiae strains is a reproducible, strain-specific and simple method that can be used successfully to monitor yeast strain population dynamics during wine fermentations.

Mannitol production by lactic acid bacteria grown in supplemented carob syrup.

Detailed kinetic and physiological characterisation of eight mannitol-producing lactic acid bacteria, Leuconostoc citreum ATCC 49370, L. mesenteroides subsp. cremoris ATCC19254, L. mesenteroides subsp. dextranicum ATCC 19255, L. ficulneum NRRL B-23447, L. fructosum NRRL B-2041, L. lactis ATCC 19256, Lactobacillus intermedius NRRL 3692 and Lb. reuteri DSM 20016, was performed using a carob-based culture medium, to evaluate their different metabolic capabilities. Cultures were thoroughly followed for 30 h to evaluate consumption of sugars, as well as production of biomass and metabolites. All strains produced mannitol at high yields (>0.70 g mannitol/g fructose) and volumetric productivities (>1.31 g/l h), and consumed fructose and glucose simultaneously, but fructose assimilation rate was always higher. The results obtained enable the studied strains to be divided mainly into two groups: one for which glucose assimilation rates were below 0.78 g/l h (strains ATCC 49370, ATCC 19256 and ATCC 19254) and the other for which they ranged between 1.41 and 1.89 g/l h (strains NRRL B-3692, NRRL B-2041, NRRL B-23447 and DSM 20016). These groups also exhibited different mannitol production rates and yields, being higher for the strains with faster glucose assimilation. Besides mannitol, all strains also produced lactic acid and acetic acid. The best performance was obtained for L. fructosum NRRL B-2041, with maximum volumetric productivity of 2.36 g/l h and the highest yield, stoichiometric conversion of fructose to mannitol.

Saccharomyces cerevisiae CCMI 885 secretes peptides that inhibit the growth of some non-Saccharomyces wine-related strains.

The nature of the toxic compounds produced by Saccharomyces cerevisiae CCMI 885 that induce the early death of Hanseniaspora guilliermondii during mixed fermentations, as well as their ability to inhibit the growth of other non-Saccharomyces wine-related strains, was investigated. The killing effect of mixed supernatants towards H. guilliermondii was inactivated by protease treatments, thus revealing the proteinaceous nature of the toxic compounds. Analysis of the protein pattern of mixed supernatants on Tricine SDS-PAGE showed that this S. cerevisiae strain secretes peptides (<10 kDa), which were detected only when death of H. guilliermondii was already established. Death-inducing supernatants were ultrafiltrated by 10 and 2 kDa membranes, respectively, and the inhibitory effect of those permeates were tested in H. guilliermondii cultures. Results indicated that the (2-10) kDa protein fraction of those supernatants seemed to contain antimicrobial peptides active against H. guilliermondii. Thus, the (2-10) kDa protein fraction was concentrated and its inhibitory effect tested against strains of Kluyveromyces marxianus, Kluyveromyces thermotolerans, Torulaspora delbrueckii and H. guilliermondii. Under the growth conditions used for these tests, the (2-10) kDa protein fraction of S. cerevisiae CCMI 885 supernatants exhibited a fungistatic effect against all the strains and a fungicidal effect against K. marxianus.

Wheat straw autohydrolysis: process optimization and products characterization.

Wheat straw was subjected to autohydrolysis treatments in order to selectively hydrolyze the hemicellulose fraction. The effects of temperature (150-240 degrees C) and non-isothermal reaction time on the composition of both liquid and solid phases were evaluated and interpreted using the severity factor (log R0). The operational conditions leading to the maximum recovery of hemicellulose-derived sugars were established for log R0 = 3.96 and correspond to 64% of the original (arabino)xylan with 80% of sugars as xylooligosaccharides. Under these conditions, a solubilization of 58% xylan, 83% arabinan, and 98% acetyl groups occurred. Glucan was mainly retained in the solid phase (maximum solubilization 16%), which enables an enrichment of the solid phase to contain up to 61% glucan. Delignification was not extensive, being utmost 15%. The yields of soluble products, including sugars, acetic acid, and degradation compounds, such as, furfural, 5-hydroxymethylfurfural furfural obtained suggest the fitness of liquid stream for fermentation purposes or to obtain xylooligosaccharides with potential applications in food, pharmaceutical, and cosmetic industries.

Dilute acid hydrolysis of wheat straw oligosaccharides.

The dilute acid posthydrolysis of wheat straw hemicellulosic oligosaccharides obtained by autohydrolysis was evaluated. An empirical model was used to describe the effect of catalyst concentration (sulfuric acid, 0.1-4% w/w) and reaction time (0-60 min) based on data from a Doehlert experimental design. Catalyst concentration is the main variable influencing posthydrolysis performance, as both its linear and quadratic coefficients are statistically significant for the majority of the studied variables, namely, the ones related to sugar and byproducts production. Reaction time influences xylose and furan derivatives concentrations but not phenolics or acetic acid content. Catalyst concentration and reaction time interact synergistically, minimizing sugar recovery and promoting furan derivatives production. Based on the proposed models, it was possible to delimit an operational range that enables to obtain high monosaccharides recovery together with a slight decrease in inhibitors content as compared to the standard acid hydrolysis treatment. Furthermore, this is achieved with up to 70% less acid spending or considerable savings on reaction time.

Assessment on the fermentability of xylooligosaccharides from rice husks by probiotic bacteria.

Liquors from rice husk autohydrolysis, containing xylooligosaccharides (XOS), other saccharides, and nonsaccharide compounds, were refined by membrane processing to increase the proportion of substituted XOS in refined liquors. XOS were assayed for composition and degree of polymerization (DP) distribution and hydrolyzed with commercial enzymes for obtaining XOS with DP in the range of 2-6. Nanofiltered, hydrolyzed liquors were subjected to ion exchange processing to yield a final product containing monosaccharides, XOS (accounting for 55.6% of the nonvolatile solutes), and other nonvolatile compounds. The solution obtained after enzymatic hydrolysis with commercial xylanases (in which 82.8% of XOS were in the DP range of 2-6) was examined as a medium for promoting the growth of Bifidobacterium adolescentis CECT 5781, B. longum CECT 4503, B. infantis CECT 4551, and B. breve CECT 4839. The growth rate of B. adolescentis (0.58 h(-1)) was higher than the ones determined for B. longum, B. infantis, and B. breve (0.37, 0.30, and 0.40 h(-1), respectively). The percentage of total XOS consumption by B. adolescentis was 77% after 24 h, the highest percentage of utilization corresponding to xylotriose (90%), followed by xylobiose (84%), xylotetraose (83%), and xylopentaose (71%).

Yeast biomass production in brewery's spent grains hemicellulosic hydrolyzate.

Yeast single-cell protein and yeast extract, in particular, are two products which have many feed, food, pharmaceutical, and biotechnological applications. However, many of these applications are limited by their market price. Specifically, the yeast extract requirements for culture media are one of the major technical hurdles to be overcome for the development of low-cost fermentation routes for several top value chemicals in a biorefinery framework. A potential biotechnical solution is the production of yeast biomass from the hemicellulosic fraction stream. The growth of three pentose-assimilating yeast cell factories, Debaryomyces hansenii, Kluyveromyces marxianus, and Pichia stipitis was compared using non-detoxified brewery's spent grains hemicellulosic hydrolyzate supplemented with mineral nutrients. The yeasts exhibited different specific growth rates, biomass productivities, and yields being D. hansenii as the yeast species that presented the best performance, assimilating all sugars and noteworthy consuming most of the hydrolyzate inhibitors. Under optimized conditions, D. hansenii displayed a maximum specific growth rate, biomass yield, and productivity of 0.34 h(-1), 0.61 g g(-1), and 0.56 g l(-1) h(-1), respectively. The nutritional profile of D. hansenii was thoroughly evaluated, and it compares favorably to others reported in literature. It contains considerable amounts of some essential amino acids and a high ratio of unsaturated over saturated fatty acids.