FACTORS PRODUCING HIGH YEAST YIELDS IN SYNTHETIC MEDIA

Comparison of microplate- and bottle-based methods to age yeast for chronological life span assays

This study compared the chronological life span and survival of Saccharomyces cerevisiae aged in a microplate or bottle, under different aeration and calorie restriction conditions. Our data shows that limited aeration in the microplate-aged culture contributed to slower outgrowth but extended yeast CLS compared to the bottle-aged culture.

Lipolytic Enzymes with Hydrolytic and Esterification Activities Produced by Filamentous Fungi Isolated from Decomposition Leaves in an Aquatic Environment

Microbial lipases are prominent biocatalysts able to catalyze a wide variety of reactions in aqueous and nonaqueous media. In this work, filamentous fungi isolated from leaves decomposed in an aquatic environment were screened for lipase production with hydrolytic activity and esterification. Agar plates with Tween 20 and Rhodamine B were used for selection, while submerged cultures with olive oil were subsequently used to select 38 filamentous fungi. Trichoderma harzianum, Fusarium solani, Trichoderma harzianum F5, and Penicillium sp. F36 were grown in six different culture media. F. solani presented the highest lipase production (2.37 U/mL) with esterification activity of 0.07 U/mL using medium composed of (g.L-1) KH2PO4 1.00, MgSO4 H2O 1.123, and CuSO4 0.06. Supplementation of this culture medium with organic nitrogen sources increased lipase production by 461.3% using tryptone and by 419.4% using yeast extract. Among the vegetable oils from the Amazon region, degummed cotton oil induced lipase production up to 8.14 U/mL. The lipase produced by F. solani F61 has great potential to application in conventional processes and biodiesel production by transesterification of vegetable oils, as well as food industries in the production of fatty acid esters by hydrolysis and esterification.

Yeast synthetic biology for the production of recombinant therapeutic proteins

The production of recombinant therapeutic proteins is one of the fast-growing areas of molecular medicine and currently plays an important role in treatment of several diseases. Yeasts are unicellular eukaryotic microbial host cells that offer unique advantages in producing biopharmaceutical proteins. Yeasts are capable of robust growth on simple media, readily accommodate genetic modifications, and incorporate typical eukaryotic post-translational modifications. Saccharomyces cerevisiae is a traditional baker's yeast that has been used as a major host for the production of biopharmaceuticals; however, several nonconventional yeast species including Hansenula polymorpha, Pichia pastoris, and Yarrowia lipolytica have gained increasing attention as alternative hosts for the industrial production of recombinant proteins. In this review, we address the established and emerging genetic tools and host strains suitable for recombinant protein production in various yeast expression systems, particularly focusing on current efforts toward synthetic biology approaches in developing yeast cell factories for the production of therapeutic recombinant proteins.

Design of an efficient medium for heterologous protein production in Yarrowia lipolytica: case of human interferon alpha 2b

Background

The non conventional yeast Yarrowia lipolytica has aroused a strong industrial interest for heterologous protein production. However most of the studies describing recombinant protein production by this yeast rely on the use of complex media, such media are not convenient for large scale production particularly for products intended for pharmaceutical applications. In addition medium composition can also affect the production yield. Hence it is necessary to design an efficient medium for therapeutic protein expression by this host.

Results

Five different media, including four minimal media and a complex medium, were assessed in shake flasks for the production of human interferon alpha 2b (hIFN α2b) by Y. lipolytica under the control of POX2 promoter inducible with oleic acid. The chemically defined medium SM4 formulated by Invitrogen for Pichia pastoris growth was the most suitable. Using statistical experimental design this medium was further optimized. The selected minimal medium consisting in SM4 supplemented with 10 mg/l FeCl₃, 1 g/l glutamate, 5 ml/l PTM1 (Pichia Trace Metals) solution and a vitamin solution composed of myo-inositol, thiamin and biotin was called GNY medium. Compared to shake flask, bioreactor culture in GNY medium resulted in 416-fold increase of hIFN α2b production and 2-fold increase of the biological activity.

Furthermore, SM4 enrichment with 5 ml/l PTM1 solution contributed to protect hIFN α2b against the degradation by the 28 kDa protease identified by zymography gel in culture supernatant. The screening of the inhibitory effect of the trace elements present in PTM1 solution on the activity of this protease was achieved using a Box-Behnken design. Statistical data analysis showed that FeCl₃ and MnSO₄ had the most inhibitory effect.

Conclusion

We have designed an efficient medium for large scale production of heterologous proteins by Y. lipolytica. The optimized medium GNY is suitable for the production of hIFN α2b with the advantage that no complex nitrogen sources with non-defined composition were required.

Critical analysis of engineering aspects of shaken flask bioreactors

Shaking bioreactors are the most frequently used reaction vessels in biotechnology. Since their inception, shaking bioreactors have been playing a significant role in medicine, agriculture, food, environmental, and industrial research. In spite of their huge practical importance, very little is known about the characteristic properties of shaken cultures from an engineering point of view. In this paper, a critical analysis is presented of the mixing characteristics, aeration, mass and heat transfer, power consumption, and suitability for on-line monitoring and control of various environmental and other operating parameters in aerated and anaerobic/anoxic conditions. Aspects of cell damage due to shear stress generated in shaken flask and loss of sterility due to contamination are also discussed.

Enhancement of oxygen transfer by pressure pulsation in aqueous glycerol fermentation

Aeration plays an important role in the production of glycerol by fermentation with yeast. Effective aeration depends on a number of factors, such as amount of air, fineness of air dispersion, rate of agitation, and time of gas-liquid contact. This investigation dealt with the effect of periodic variation in gas pressure on oxygen transfer measured by sulfite oxidation and glycerol fermentation in stirred tanks. The oxygen transfer rate measured with the sulfite oxidation method was improved by 20-30% under the condition of pressure pulsation (PP) at 30 degrees C. The yield and productivity of glycerol were increased by about 26 and 6.8%, respectively, in 48 h by employing a glucose concentration of 250 g/L with PP at 30 degrees C.

Yeast cell attachment: a tool modulating wall composition and resistance to 5-bromo-6-azauracil

The attachment of Candida utilis, Kluyveromyces lactis, and Saccharomyces cerevisiae cells stimulates an increase in the content of cell wall polysaccharides and mannoproteins, accompanied by increased resistance to the inhibitory effect of 5-bromo-6-azauracil. The covalent attachment of viable yeasts was accomplished (via dialdehyde-amino spacers) by reaction of aldehyde groups of the carrier with reactive amino groups in accessible cell surface proteins. The employed technique enables the optimization of yeast sources of beta-1,3-, beta-1,6- glucans, mannan, and mannoprotein. The modulatory effect of the cell attachment is discussed.

Boron stimulates yeast (Saccharomyces cerevisiae) growth

Boron is required for the growth of vascular plants and embryonic development in fish. The molecular basis of boron's essentiality, however, remains unknown for both. The objective of this study was to determine whether yeast (Saccharomyces cerevisiae) could be used as a model for the evaluation of intracellular boron trafficking. Three experiments were conducted to assess the effect of boron supplementation on yeast growth. Cultures were grown in low boron media containing 0.04 micromol B/L. After 24 h, a new flask was inoculated with this culture; it was allowed to reach early log phase growth (9 h) and was then divided between two flasks. One flask was supplemented with ultrapure boric acid to achieve a concentration of 185 micromol B/L (+B); the other was supplemented with an equivalent volume of ultrapure water (NB). Boron significantly stimulated cell growth rate into the stationary phase of growth. Yeast cell boron concentrations decreased in both treatments over the course of the experiment, but analysis by inductively coupled plasma-mass spectrometry (ICPMS) did not detect differences in cellular concentration between the boron supplemented (B) and nonsupplemented (NB) groups. Ethanol concentrations did not differ between the two treatments, demonstrating that boron-stimulated growth was not a secondary effect of alcohol dehydrogenase inhibition. The demonstration of boron-dependent growth stimulation in yeast suggests that Saccharomyces cerevisiae can be used as a model system for the study of intracellular boron trafficking.

Citric acid fermentation of sugars purified with chelating resin

Noguchi, Yuichi (University of Wisconsin, Madison), and Marvin J. Johnson. Citric acid fermentation of sugars purified with chelating resin. J. Bacteriol. 82:538-541. 1961.-A new, independently isolated strain of Aspergillus niger capable of giving high yields of citric acid in submerged culture was found to show the same behavior toward iron, zinc, and manganese as a previously studied strain. Citric acid accumulation did not occur in the presence of manganese. Best citric acid production was obtained in the presence of limited amounts of iron and zinc. Use of a chelating ion exchange resin was found to be an excellent method of removing polyvalent metals from sugars, either for analytical purposes or for fermentation. Commercial glucose, after resin treatment, gave citric acid yields of more than 80% when supplemented with iron and zinc. Unpurified glucose was converted to citric acid in good yields by mycelium grown on resin-treated glucose.

MULTIPLE SCARS, A NEW TYPE OF YEAST SCAR IN APICULATE YEASTS

Streiblová, Eva (Czechoslovak Academy of Sciences, Prague, Czechoslovakia), K. Beran, and V. Pokorný. Multiple scars, a new type of yeast scar in apiculate yeasts. J. Bacteriol. 88:1104-1111. 1964.-A new type of yeast scar is described in apiculate yeasts: Saccharomycodes, Nadsonia, Hanseniaspora, and Kloeckera. These scars are formed on the distal poles of the cell walls in the course of vegetative reproduction, and are the cause of the formation of the apiculate form of the cells. The structure of multiple scars was studied by fluorescence microscopy and by electron microscopy on carbon replicas and isolated cell walls. The discussion deals with the importance of described cytological structures for the morphogenesis of cells and for determining individual reproductive capacity of cells, and considers some questions related to the interpretation of the development of multiple scars.

EFFECT OF OXYGEN-SUPPLY RATES ON GROWTH OF ESCHERICHIA COLI. II. COMPARISON OF RESULTS IN SHAKE FLASKS AND 50-LITER FERMENTOR

Growth of Escherichia coli and chemical changes in the medium were very similar in highly baffled flasks and in a 50-liter fermentor run under the same oxygen-supply conditions, based on sulfite-oxidation rates. Flasks with stainless-steel baffles (Biotech) gave growth patterns and rates of glucose and NH(4)-N utilization almost identical to those of the fermentor; results with Bellco 598 flasks (with 6 to 7 mm deep indentations) were quite similar. Unbaffled and Bellco 600 flasks (3 to 4 mm indentations) were similar to the fermentor at very high and very low oxygen-transfer rates, but gave much less growth than the fermentor at intermediate levels. Maximal oxygen-uptake rates occurred in the fermentor at the end of the logarithmic-growth phase when growth was 40 to 75% of maximum. In the fermentor, both sulfite-oxidation rates and rates of oxygen uptake correlated reasonably well with the total amount of growth produced.

D-ARABITOL PRODUCTION BY ENDOMYCOPSIS CHODATI

Endomycopsis chodati in an aerated fermentation produced d-arabitol in yields of 35 to 40% of the sugar supplied. Glucose, mannose, and sucrose were suitable substrates. A synthetic medium was developed for the fermentation that showed that nitrogen in the medium must be limiting to obtain high yields of arabitol. Excess phosphate also tended to lower arabitol yields, although the effect was not so great as with nitrogen. Pilot plant-size fermentations were made in which all the nutrients were supplied by blackstrap molasses and urea. Arabitol yields in these fermentations were about 40% of the sugar supplied.

ERYTHRITOL PRODUCTION BY A YEASTLIKE FUNGUS

A yeastlike fungus, probably belonging to the genus Torula, was isolated from fresh pollen and was shown to produce erythritol in yields of 35 to 40% of the sugar utilized. The ability to produce erythritol is an inherent characteristic of the isolate, but unfavorable fermentation conditions can lead to the production of glycerol at the expense of erythritol. By the use of a synthetic medium, it was shown that the concentrations of both nitrogen and phosphorous in the medium must be closely controlled to obtain satisfactory erythritol yields.

Covalent immobilization as a stimulus of cell wall composition changes

Covalent immobilization of yeast cells by an activated diamine spacer is accompanied by increased levels of cell wall proteins, lipids, amino sugars, amino acids and acid phosphatase leakage, and by altered composition of mannoproteins. The observed changes in cell wall composition are attributed to the effect of cell-solid surface contact.

Regulation of sterol biosynthesis in Saccharomyces cerevisiae

Sterol synthesis in Saccharomyces cerevisiae was primarily controlled by the growth rate. At low specific growth rates the intermediates of ergosterol biosynthesis prevailed in cells. At the same time, the total sterol content reached about 6% of dry matter whereas the content of ergosterol was only 2-2.5%, which seems to be the maximum value for S. cerevisiae. After esterification with fatty acids these sterol intermediates are stored in lipid globules together with reserve triacylglycerols. The sporulating S. cerevisiae cells contained 3.5% sterols and 1.5% ergosterol of dry matter.

Dimorphic growth and lipase production in lipolytic yeasts

N-Acetylglucosamine and citrate promoted intensive dimorphic growth and significant lipase synthesis in Yarrowia lipolytica. In contrast, use of a phosphate buffer instead of citrate for buffering the medium stimulated only dimorphic growth. No correlation between dimorphic growth and a high lipase synthesis studied in five different species of lipolytic yeasts was demonstrated. The data provide evidence against the inevitable linkage between the capability (and/or intensity) of mycelium formation and a high level of extracellular lipase in lipolytic yeasts.

Turnover of canavanine-containing proteins in Saccharomyces cerevisiae

Saccharomyces cerevisiae grown for 2 h in the presence of 0.5 mmol/L canavanine in a synthetic medium with ethanol as the sole carbon source (OEC) exhibited a slowing down of protein synthesis for 3-4 h after a shift to fresh ethanol-based medium containing 1.0 mmol/L arginine (OEA) in comparison with untreated cells grown on OEA. The change of carbon source from ethanol to glucose (OGA) after growth in the OEC medium resulted in an even deeper decline of protein synthesis. The degradation of canavanine-containing proteins in cells pregrown and labelled in an OEC medium after transfer to OEA was more rapid than in the OGA medium. The initial rate of protein degradation during the first hour in the OGA medium was less than 1%/h whereas in the OEA medium it reached almost 10%/h. The fraction of proteins with high turnover (half-life 0.46 h) constituted 8.3% on OEA, while during subsequent growth on OGA it was only 0.75% with a half-life of 0.12 h.

Effect of nitrogen limitation and sporulation on sterol and lipid formation in Saccharomyces cerevisiae

The content of sterols and lipids was compared in the cells of Saccharomyces cerevisiae cultivated in sporulation and the sterol-induction nitrogen-limited media. After 24 h the measured values in the two cultivations did not significantly differ. However, after subsequent 24 h, further formation of lipid globules and a corresponding increase of lipid and sterol content was detected only in the sterol-induction medium. To demonstrate the similarity of physiological state during the first day of the two cultivations, the combined cultivations were performed. Maximum sporulation, suggesting maximum similarity, of the two processes was achieved when the cells were grown in the sterol-induction medium for 15 h and then transferred to a sporulation medium.

Effect of growth rate on ethanol tolerance of Saccharomyces cerevisiae

delta 5,7-Sterol-accumulating Saccharomyces cerevisiae cells growing in chemostat at a specific growth rate of 0.075/h exhibited higher ethanol tolerance measured as ethanol-induced death and anaerobic growth inhibition than the cells growing at 0.2/h, the difference being dependent on the carbon-to-nitrogen molar proportion in the medium. The observed difference in sensitivity to ethanol of anaerobic growth between the slowly and rapidly-growing cells was completely reversed as a result of a block in sterol synthesis causing a negligible synthesis of delta 5,7-sterols. Two physiological parameters, budding frequency and membrane composition, evidently affected ethanol tolerance. Differences between the delta 5,7-sterol-synthesizing and deficient strains documented a profound effect of the quality of the sterol present on the physiological state of the cell.

Increased sterol formation in Saccharomyces cerevisiae. Analysis of cell components and ultrastructure of vacuoles

In Saccharomyces cerevisiae nitrogen limitation under aerobic conditions (low specific growth rate) provokes an enhanced synthesis of sterols. Analysis of east cultures during the enhanced sterol biosynthesis showed a temporary decrease of protein content and a simultaneous increase in polysaccharide and lipid levels. This was reflected in the ultrastructure of cells where numerous lipid globules (spherosomes, oleosomes) appeared around extensive membrane-bound compartments containing membrane vesicles and lipoprotein material. Electronograms showed that such compartments were formed between the layers of endoplasmic reticulum and belonged to the vacuome phase of the yeast cell. It appears that vacuoles formed in yeast during enhanced synthesis of sterols have a storage rather than a lysosomal function.