Influence of the concentrations of d-xylose and yeast extract on ethanol production by Pachysolen tannophilus

To determine the most favorable conditions for the production of ethanol by Pachysolen tannophilus, this yeast was grown in batch cultures with various initial concentrations of two of the constituents of the culture medium: d-xylose (s_o), ranging from 1 g·l⁻¹ to 200 g·l⁻¹, and yeast extract (l_o), ranging from 0 g·l⁻¹ to 8 g·l⁻¹. The most favorable conditions proved to be initial concentrations of S_o=25 g·l⁻¹ and l_o=4 g·l⁻¹, which gave a maximum specific growth rate of 0.26 h⁻¹, biomass productivity of 0.023 g·l⁻¹·h⁻¹, overall biomass yield of 0.094 g·g⁻¹, specific xylose-uptake rate (q_s) of 0.3 g·g⁻¹·h⁻¹ (for t=50 h), specific ethanol-production rate (q_E) of 0.065 g·g⁻¹·h⁻¹ and overall ethanol yield of 0.34 g·g⁻¹; q_s values decreased after the exponential growth phase while q_E remained practically constant.     

Optimal C:N ratio for the production of red pigments by Monascus ruber

The carbon-to-nitrogen (C:N) ratio in the biomass of microfungi tends to be quite different (e.g. 10–15) compared with the C:N ratio in the red pigments (e.g. >20) of the fungus Monascus ruber. Therefore, determining an optimal C:N ratio in the culture medium for maximizing the production of the pigments is important. A culture medium composition is established for maximizing the production of the red pigment by the fungus M. ruber ICMP 15220 in submerged culture. The highest volumetric productivity of the red pigment was 0.023 AU L^?1 h^?1 in a batch culture (30 °C, initial pH of 6.5) with a defined medium of the following composition (g L^?1): glucose (10), monosodium glutamate (MSG) (10), MgSO₄·7H₂O (0.5), KH₂PO₄ (5), K₂HPO₄ (5), ZnSO₄·7H₂O (0.01), FeSO₄·7H₂O (0.01), CaCl₂ (0.1), MnSO₄·H₂O (0.03). This medium formulation had a C:N mole ratio of 9:1. Under these conditions, the specific growth rate of the fungus was 0.043 h^?1 and the peak biomass concentration was 6.7 g L^?1 in a 7-day culture. The biomass specific productivity of the red pigment was 1.06 AU g^?1 h^?1. The best nitrogen source proved to be MSG although four other inorganic nitrogen sources were evaluated.     

Effect of controlled oxygen limitation on Candida shehatae physiology for ethanol production from xylose and glucose

Carbon distribution and kinetics of Candida shehatae were studied in fed-batch fermentation with xylose or glucose (separately) as the carbon source in mineral medium. The fermentations were carried out in two phases, an aerobic phase dedicated to growth followed by an oxygen limitation phase dedicated to ethanol production. Oxygen limitation was quantified with an average specific oxygen uptake rate (OUR) varying between 0.30 and 2.48 mmolO₂ g dry cell weight (DCW)^?1 h^?1, the maximum value before the aerobic shift. The relations among respiration, growth, ethanol production and polyol production were investigated. It appeared that ethanol was produced to provide energy, and polyols (arabitol, ribitol, glycerol and xylitol) were produced to reoxidize NADH from assimilatory reactions and from the co-factor imbalance of the two-first enzymatic steps of xylose uptake. Hence, to manage carbon flux to ethanol production, oxygen limitation was a major controlled parameter; an oxygen limitation corresponding to an average specific OUR of 1.19 mmolO₂ g DCW^?1 h^?1 allowed maximization of the ethanol yield over xylose (0.327 g g^?1), the average productivity (2.2 g l^?1 h^?1) and the ethanol final titer (48.81 g l^?1). For glucose fermentation, the ethanol yield over glucose was the highest (0.411 g g^?1) when the specific OUR was low, corresponding to an average specific OUR of 0.30 mmolO₂ g DCW^?1 h^?1, whereas the average ethanol productivity and ethanol final titer reached the maximum values of 1.81 g l^?1 h^?1 and 54.19 g l^?1 when the specific OUR was the highest.     

CELL CYCLE AND ACCUMULATION OF ASTAXANTHIN IN HAEMATOCOCCUS LACUSTRIS (CHLOROPHYTA)1

Synchronous release of ellipsoidal biflagellated zoo-spores from thick-walled akinetes of Haematococcus lacustris (Gir.) Rostaf. (UTEX 16) was induced. After being released, the zoospores divided rapidly at a rate that depended on the initial concentration of urea in the culture medium. Cells fused after approximately five doublings, and the DNA content of most cells doubled within 50 h. Spherical nonmotile palmella cells and aplanospores appeared after 100 h of incubation in media containing high (1.7 g·L^?1) and low (0.85 g·L^?1) urea concentrations. Thereafter, the number of nonmotile cells increased with time, whereas motile cell numbers decreased with time. Nonmotile cells continued to grow and divide by forming 4–32 aplanospores, for up to 200 h of incubation in the high-urea medium. The size of the nonmotile cells and the number of daughter cells formed within was inversely proportional to the growth rate of the cultures. Within the first 100 h of incubation, dry weight biomass of the zoo-spores increased from about 0.3 to 0.8 g·L^?1. In the following 180 h, dry weight biomass reached 1.7 g·L^?1 in the low-urea medium and 2.5 g·L^?1 in the high-urea medium. The astaxanthin content of zoospores decreased with time, whereas there was a net accumulation of astaxanthin in the nonmotile cells. The specific rate of accumulation of astaxanthin in motile and nonmotile cells, however, was practically identical.     

The activity of beta-galactosidase and lactose metabolism in Kluyveromyces lactis cultured in cheese whey as a function of growth rate

Aims: Kluyveromyces lactis was cultured in cheese whey permeate on both batch and continuous mode to investigate the effect of time course and growth rate on β‐galactosidase activity, lactose consumption, ethanol production and protein profiles of the cells. Methods and Results: Cheese whey was the substrate to grow K. lactis as a batch or continuous culture. In order to precise the specific growth rate for maximum β‐galactosidase activity a continuous culture was performed at five dilution (growth) rates ranging from 0·06, 0·09, 0·12, 0·18 to 0·24 h^?1. The kinetics of lactose consumption and ethanol production were also evaluated. On both batch and continuous culture a respirofermentative metabolism was detected. The growth stage for maximum β‐gal activity was found to be at the transition between late exponential and entrance of stationary growth phase of batch cultures. Fractionating that transition stage in several growth rates at continuous culture a maximum β‐galactosidase activity at 0·24 h^?1 was observed. Following that stage β‐gal activity undergoes a decline which does not correlate to the density of its corresponding protein band on the gel prepared from the same samples. Conclusion: The maximum β‐galactosidase activity per unit of cell mass was found to be 341·18 mmol ONP min^?1 g^?1 at a dilution rate of 0·24 h^?1. Significance and Impact of the Study: The physiology of K. lactis growing in cheese whey permeate can proven useful to optimize the conversion of that substrate in biomass rich in β‐gal or in ethanol fuel. In addition to increasing the native enzyme the conditions established here can be set to increase yields of recombinant protein production based on the LAC4 promoter in K. lactis host.     

Enhanced production of erythritol by Yarrowia lipolytica on glycerol in repeated batch cultures

Erythritol is an important natural sweetener, industrially produced only by fermentation on glucose media. Glycerol is an important renewable feedstock as it is the major by-product of the biodiesel production process; here we present an alternative way to convert this low-cost substrate into value-added products, such as erythritol. Repeated batch cultures (RBC) were performed to improve the productivity of erythritol from pure and crude glycerol. An acetate negative mutant of Yarrowia lipolytica Wratislavia K1 was found to be applicable for the production of high amounts of erythritol in RBC. When 20 % of fresh replaced medium was added, the strain Wratislavia K1 was able to produce 220 g l ^?1 erythritol, which corresponded to a 0.43 g g^?1 yield and a productivity of 0.54 g l^?1 h^?1. Additionally, the activity of the culture remained stable for more than 1,000 h, i.e., 11 cycles of the repeated batch bioreactors.     

Kinetic study of Lactococcus lactis strains (SLT6 and SLT10) growth on papain-hydrolysed whey

The effect of controlled whey hydrolysis by papain on growth of two lactic acid bacteria isolated from artisanal Leben: Lactococcus lactis var. diacetylactis (SLT6 and SLT10) was investigated. The higher biomass and maximum specific growth rate (μ _max) were obtained after 30 min of hydrolysis. HPLC analysis of peptides showed that whey hydrolysis reduced the amount of peptides of MW > 400 Da and increased those peptides of MW < 400 Da. The two studied strains exhibited different peptide requirements. The pH-controlled batch cultures in 30 min hydrolysed whey followed the Monod kinetic for growth and for lactate production. The values of the key kinetic constants were: maximum specific growth rate (μ _max), 1.08 and 0.56 h^?1; yield biomass on lactose (Y _x/s), 0.20 and 0.18 g g^?1 and saturation constant K _s, 4.2 and 2.8 g L^?1 for SLT6 and SLT10, respectively. When compared with batch experimental data, the model provided good predictions for growth, lactose utilisation and lactate production profiles.     

Poly(β-hydroxybutyric acid) thermoplastic production by Alcaligenes latus: Behavior of fed-batch cultures

Fed-batch culture of Alcaligenes latus, ATCC 29713, was investigated for producing the intracellular bioplastic poly(β–hydroxybutyric acid), PHB. Constant rate feeding, exponentially increasing feeding rate, and pH-stat fed batch methods were evaluated. pH-stat fed batch culture reduced or delayed accumulation of the substrate in the broth and led to significantly enhanced PHB productivity relative to the other modes of feeding. Presence of excessive substrate appeared to inhibit PHB synthesis, but not the production of cells. In fed-batch culture, the maximum specific growth rate (0.265?h^?1) greatly exceeded the value (0.075?h^?1) previously observed in batch culture of the same strain. Similarly, the maximum PHB production rate (up to 1.15?g?·?l^?1?·?h^?1) was nearly 8-fold greater than values observed in batch operations. Fed-batch operation was clearly superior to batch fermentation for producing PHB. A low growth rate was not a prerequisite for PHB accumulation, but a reduced or delayed accumulation of substrate appeared to enhance PHB accumulation. Under the best conditions, PHB constituted up to 63% of dry cell mass after 12?h of culture. The average biomass yield coefficient on sucrose was about 0.35, or a little less than in batch fermentations. The highest PHB concentrations attained were about 18?g?·?l^?1.     

Evaluation of ethanol production by a new isolate of yeast during fermentation in synthetic medium and sugarcane bagasse hemicellulosic hydrolysate

A new xylose fermenting yeast was isolated from over-ripe banana by enrichment in xylose-containing medium. The phylogenetic analysis of ITS1-5.8S-ITS2 region sequences of ribosomal RNA of isolate BY2 revealed that it shows affiliation to genus Pichia and clades with Pichia caribbica. In batch fermentation, Pichia strain BY2 fermented xylose, producing 15 g l^?1 ethanol from 30 g l^?1 xylose under shaking conditions at 28°C, with ethanol yield of 0.5 g g^?1 and volumetric productivity of 0.31 g l^?1 h^?1. The optimum pH range for ethanol production from xylose by Pichia strain BY2 was 5–7. Pichia strain BY2 also produced 6.08 g l^?1 ethanol from 30 g l^?1 arabinose. Pichia strain BY2 can utilize sugarcane bagasse hemicellulose acid hydrolysate for alcohol production, efficiency of fermentation was improved by neutralization, and sequential use of activated charcoal adsorption method. Percent total sugar utilized and ethanol yield for the untreated hydrolysate was 17.14% w/v and 0.33 g g^?1, respectively, compared with 66.79% w/v and 0.45 g g^?1, respectively, for treated hemicellulose acid hydrolysate. This new yeast isolate showed ethanol yield of 0.45 g g^?1 and volumetric productivity of 0.33 g l^?1 h^?1 from sugarcane bagasse hemicellulose hydrolysate detoxified by neutralization and activated charcoal treatment, and has potential application in practical process of ethanol production from lignocellulosic hydrolysate.     

Recombinant Protein Production with Pichia pastoris in Continuous Fermentation – Kinetic Analysis of Growth and Product Formation

Continuous fermentation was applied to the production of recombinant human chymotrypsinogen B (hCTRB) by the methylotrophic yeast Pichia pastoris as a tool for the kinetic analysis of growth and product formation. Using methanol as the sole source of carbon, energy, and induction, cell growth could be described by a non‐competitive Monod approach. Maximum growth rate μ_max was determined to 0.084 h^‐‐1 and the K_M‐value for methanol to 0.22 g·L^‐‐1, respectively. With respect to product formation, a similar model was established exhibiting a methanol concentration of 0.13 g·L^‐‐1 as the K_M‐value and a maximum biomass‐specific product‐formation rate of π_max = 0.23 mg·g^‐‐1·h^‐‐1. The production of hCTRB was strictly growth‐coupled. The data provided covers the range of methanol concentrations between 0 and 4 g·L^‐‐1. Substrate concentrations exceeding this upper value led to a complete collapse of product formation. This change in phenotype turned out to be irreversible indicating a genetic instability of transformed Pichia pastoris caused by excess methanol.     

The citric acid production from raw glycerol by Yarrowia lipolytica yeast and its regulation

The optimal cultivation conditions ensuring the maximal rate of citric acid (CA) biosynthesis by glycerol-grown mutant Yarrowia lipolytica NG40/UV7 were found to be as follows: growth limitation by inorganic nutrients (nitrogen, phosphorus, or sulfur), 28 °C, pH 5.0, dissolved oxygen concentration (pO₂) of 50 % (of air saturation), and pulsed addition of glycerol from 20 to 80 g L^?1 depending on the rate of medium titration. Under optimal conditions of fed-batch cultivation, in the medium with pure glycerol, strain Y. lipolytica NG40/UV7 produced 115 g L^?1 of CA with the mass yield coefficient of 0.64 g g^?1 and isocitric acid (ICA) amounted to 4.6 g L^?1; in the medium with raw glycerol, CA production was 112 g L^?1 with the mass yield coefficient of 0.90 g g^?1 and ICA amounted to 5.3 g L^?1. Based on the activities of enzymes involved in the initial stages of raw glycerol assimilation, the tricarboxylic acid cycle and the glyoxylate cycle, the mechanism of increased CA yield from glycerol-containing substrates in Y. lipolytica yeast was explained.     

Metabolic,physiological and kinetic aspects of the alcoholic fermentation of whey permeate by Kluyveromyces fragilis NRRL 665 and Kluyveromyces lactis NCYC 571

Optimum growth conditions for the fermentation of non-concentrated whey permeate by Kluyveromyces fragilis NRRL 665 have been defined. Use of 3.75 g yeast extract l^?1, a growth temperature of 38°C and a pH of 4.0 allowed a maximum productivity of 5.23 g ethanol l^?1 h^?1 in continuous culture with a yield 91% of theoretical. Complete batch fermentation of permeate with 100 g lactose l^?1 was possible with a maximum specific growth rate of 0.276 h^?1 without any change in ethanol yield. Fermentation of concentrated permeate resulted, however, in a general decrease of specific substrate consumption rate, demonstrated by the inability to completely convert an initial 90 or 150 g lactose l^?1 in continuous culture, even at dilution rates as low as 0.05 and 0.08 h^?1, respectively. The decrease could be related to substrate inhibition, to an increase in osmotic pressure caused by lactose and salts, and to ethanol inhibition of both alcohol and biomass yield. The decrease in specific productivity could be counterbalanced by use of high cell density cultures, obtained by cell recycle of K. fragilis. Fermentation of a non-concentrated permeáte at a dilution rate of 1 h^?1 resulted in a productivity of 22 g l^?1 h^?1 at 22 g ethanol l^?1. Cell recycle using flocculating Kluyveromyces lactis NCYC 571 was also tested. With this strain a productivity of 9.3 g l^?1 h^?1 at 45 g product l^?1 was attained at a dilution rate of 0.2 h^?1, with an initial lactose concentration of 95 g l^?1.     

Diacetyl fermentation coupled with pervaporation using oleyl alcohol supported liquid membrane

Pervaporation using oleyl alcohol supported liquid membrane was successfully applied to diacetyl fermentation by immobilized lactic acid bacteria. Diacetyl productivity was about 10 g·m⁻³·h⁻¹, while productivity during batch fermentation was about 6 g·m⁻³·h⁻¹. Diacetyl yield from consumed glucose was about 0.04 g·g⁻¹ which was 4 times as large as that of batch fermentation. The pervaporation functioned favorably on actual fermentation broth. The flux of the permeate and the diacetyl separation factor for the pervaporation were about 9 g·m⁻²·h⁻¹ and 36, respectively, and these values were maintained at almost constant levels during fermentation. Diacetyl concentration in the permeate was about 2 kg·m⁻³, which is sufficiently high for commercial use.     

Prodigiosin formation by Serratia marcescens in a chemostat

In a study of the control of metabolite formation, prodigiosin production by Serratia marcescens was used as a model. Specific production rates of prodigiosin formation were determined using batch culture technique. Sucrose as carbon source and NH₄NO₃ as nitrogen source resulted in a specific production rate of 0.476 mg prodigiosin (g cell dry weight)⁻¹ h⁻¹. Prodigiosin formation and productivity was inversely correlated to growth rate when the bacterium was grown under carbon limitation on a defined medium in a chemostat culture. The maximum specific growth rate (μ_max) was 0.54 h⁻¹ and prodigiosin was formed in amounts over 1 mg l⁻¹ up to a growth rate (μ) of 0.3 h⁻¹ at steady state conditions. At a dilution rate of 0.1 h⁻¹ growth at steady state with carbon and phosphate limitation supported prodigiosin formation giving a similar specific yield [1.17 mg prodigiosin (g cell dry weight)⁻¹ and 0.94 mg g⁻¹, respectively], however, cells grown with nitrogen limitation [(NH₄)₂SO₄] did not form prodigiosin. Productivity in batch culture was 1.33 mg l⁻¹ h⁻¹ as compared to 0.57 mg l⁻¹ h⁻¹ in the chemostat.     

Anaerobic fermentation of fructose in a mixed culture of fermentative and methanogenic bacteria

Summary Two newly isolated strains of Methanosarcina, strains JKAD and DALS, were grown in monoculture and in mixed culture in combination with Acetobacterium woodii WB1. Methanosarcina strains convert acetate into methane and carbon dioxide while Acetobacterium woodii grows on fructose, producing acetate via homoacetate fermentation. Monocultures of A. woodii in continuous culture consumed up to 6 mmoles g^-1 dry weight (dw) h^-1 of fructose and produced up to 12.9 mmoles g^-1 dw h^-1 of acetate at a dilution rate (D) of 0.13 h^-1. In batch growth the methanogenic bacteria produced up to 12.1 mmoles g^-1 dw h^-1 of CH₄ at a specific growth rate of 0.043 h^-1. In continuous cultivation the specific growth rate and the specific methane production of Methanosarcina were lower than in batch cultures, with values of 0.031 h^-1 and 3.1 mmoles g^-1 dw h^-1 of methane, respectively. In combination, A. woodii and Methanosarcina strain DALS in batch cultures completely converted fructose to methane and carbon dioxide with a maximum specific methane production rate of 1.9 mmoles g^-1 dw h^-1 of methane. In continuous cultivation these mixed cultures produced between 1.2 and 2 mmoles g^-1 dw h^-1 of CH₄ at a dilution rate of up to 0.043 h^-1. The methanogens were washed out at D values higher than 0.043 h^-1 for A. woodii and Methanosarcina strain JKAD, and higher than 0.05 h^-1 for A. woodii and Methanosarcina strain DALS. Data obtained from defined mixed cultures allow one to follow interactions in a mixed population of two species with different growth constants.     

Optimization of gluconic acid synthesis by removing limitations and inhibitions

The optimization task was performed using the gluconic acid synthesis by the Acetobacter methanolicusMB 58 strain. The microorganisms were grown continuously on methanol as the growth substrate. After finishing the growth process by the deficiency of N and P, the gluconic acid synthesis was started by adding glucose. The synthesis process was performed continuously. The oxygen transfer rate depended on the gluconic acid concentration. During the growth process, the oxygen transfer rate reached a value of about 13 g O₂ · kg^?1 · h^?1using a 30-l glass fermenter equipped with a 6 blade stirrer and fully baffled. This rate declined to a value of between 2 and 5 g O₂ · kg^?1 · h^?1 in the presence of gluconic acid concentrations above 150 g gluconic acid · kg^?1medium. The yield (g gluconic acid · g^?1glucose) depended on the gluconic acid concentration and amounted to y = 0.7 in relation to 150 g gluconic acid · kg^?1medium and y = 0.8 in relation to 200 g · kg^?1medium, respectively. The fermenters were coupled with ultrafiltration moduls (Fa. ROMICON and Fa. SARTORIUS). The biomass concentrations amounted from 5 to 40 g dry mass kg^?1medium. The ultrafiltration modules retained the biomass within the fermentation system. A glucose solution (30 to 50 weight percent glucose) was continuously dosed into the fermenter. The retention time was chosen between 2 and 30 h. The gluconic acid synthesis rate reached values of up to 32 g gluconic acid · kg^?1 · h^?1. Within a range of up to 250 g gluconic acid · kg^?1medium, the acid concentration had no influence on the enzyme activity.     

A Review of: “North-Holland Publishing Company,Amsterdam, New York,Oxford, 1976; Softbound, 290 pages, $ 19.25.”

Several factors affecting erythritol production from glycerol by Yarrowia lipolytica Wratislavia K1 strain were examined in batch fermentations. Ammonium sulfate, monopotassium phosphate, and sodium chloride were identified as critical medium components that determine the ratio of polyols produced. The central composite rotatable experimental design was used to optimize medium composition for erythritol production. The concentrations of ammonium sulfate, monopotassium phosphate, and sodium chloride in the optimized medium were 2.25, 0.22, and 26.4 g L^?1, respectively. The C:N ratio was found as 81:1. In the optimized medium with 100 g L^?1 of glycerol the Wratislavia K1 strain produced 46.9 g L^?1 of erythritol, which corresponded to a 0.47 g g^?1 yield and a productivity of 0.85 g L^?1 hr^?1. In the fed-batch mode and medium with the total concentration of glycerol at 300 g L^?1 and C:N ratio at 81:1, 132 g L^?1 of erythritol was produced with 0.44 g g^?1 yield and a productivity of 1.01 g L^?1 hr^?1.     

COMPARISON OF DEVELOPMENT AND PHOTOSYNTHETIC GROWTH FOR FILAMENT CLUMPS AND REGENERATED MICROPLANTLET CULTURES OF AGARDHIELLA SUBULATA (RHODOPHYTA, GIGARTINALES)

Two axenic, in vitro liquid suspension cultures were established for Agardhiella subulata (C. Agardh) Kraft et Wynne, and their growth characteristics were compared. This study illustrated how reliable routes for the development of suspension cultures of macrophytic red algae of terete thallus morphology can be achieved for biotechnology applications. Undifferentiated filament clumps of 2–8 mm diameter were established by induction of callus-like tissue from thallus explants, and lightly branched microplantlets of 2–10 mm length were established by regeneration of filament clumps. The filament clumps were susceptible to regeneration. Adventitious shoot formation was reliably induced from 40% to 70% of the filament clumps by gentle mixing at 100 rev min^?1 on an orbital shaker. The specific growth rate of the microplantlets was higher than the filament clumps in nonagitated well plate culture (4%–6% per day for microplantlets vs. 2%–3% per day for filament clumps) at 24° C and 8–36 μmol photons·m^?2·s^?1 irradiance (10:14 h LD cycle) when grown on ASP12 artificial seawater medium at pH 8.6–8.9 with 20%–25% per day medium replacement. Oxygen evolution rate vs. irradiance measurements showed that relative to the filament clumps, microplantlets had a higher maximum specific oxygen evolution rate (P_o,max= 0.181 ± 0.035 vs. 0.130 ± 0.023 mmol O₂·g^?1 dry cell mass·h^?1), but comparable respiration rate (Q_o= 0.040 ± 0.013 vs. 0.033 ± 0.017 mmol O₂·g^?1 dry cell mass·h^?1), compensation point (I_c= 3.8 ± 2.4 vs. 5.7 ± 1.2 μmol photons·m^?2·s^?1), and light intensity at 63.2% of saturation (I_k= 17.5 ± 3.9 vs. 14.9 ± 2.6 μmol photons·m^?2·s^?1). The microplantlet culture was more suitable for suspension culture development than the filament clump culture because it was morphologically stable and exhibited higher growth rates.     

Improved β-carotene production of Rhodotorula glutinis in fermented radish brine by continuous cultivation

Fermentation kinetics of growth and β-carotene production by Rhodotorula glutinis DM28 in batch and continuous cultures using fermented radish brine, a waste generated from fermented vegetable industry, as a cultivation medium were investigated. The suitable brine concentration for β-carotene production by R. glutinis DM28 was 30 g l^?1. Its growth and β-carotene production obtained by batch culture in shake flasks were 2.2 g l^?1 and 87 μg l^?1, respectively, while, in a bioreactor were 2.6 g l^?1 and 186 μg l^?1, respectively. Furthermore, its maximum growth rate and β-carotene productivity in continuous culture obtained at the dilution rate of 0.24 h^?1 were 0.3 g l^?1 h^?1 and 19 μg l^?1 h^?1, respectively, which were significantly higher than those in the batch. Therefore, improved growth rate and β-carotene productivity of R. glutinis in fermented radish brine could be accomplished by continuous cultivation.     

Evaluation of the tolerance of acetic acid and 2-furaldehyde on the growth of Pichia stipitis and its respiratory deficient

The use of lignocellulosic residues for ethanol production is limited by toxic compounds in fermenting yeasts present in diluted acid hydrolysates like acetic acid and 2-furaldehyde. The respiratory deficient phenotype gives the cell the ability to resist several toxic compounds. So the aim of this work was to evaluate the tolerance to toxic compounds present in lignocellulosic hydrolysates like acetic acid and 2-furaldehyde in Pichia stipitis and its respiratory deficient strains. The respiratory deficient phenotype was induced by exposure to chemical agents such as acriflavine, acrylamide and rhodamine; 23 strains were obtained. The selection criterion was based on increasing specific ethanol yield (g ethanol g^?1 biomass) with acetic acid and furaldehyde tolerance. The screening showed that P. stipitis NRRL Y-7124 ACL 2-1RD (lacking cytochrome c), obtained using acrylamide, presented the highest specific ethanol production rate (1.82 g g^?1 h^?1). Meanwhile, the ACF8-3RD strain showed the highest acetic acid tolerance (7.80 g L^?1) and the RHO2-3RD strain was able to tolerate up to 1.5 g L^?1 2-furaldehyde with a growth and ethanol production inhibition of 23 and 22 %, respectively. The use of respiratory deficient yeast phenotype is a strategy for ethanol production improvement in a medium with toxic compounds such as hydrolysed sugarcane bagasse amongst others.