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PubMed1999

Differentiation between brewing and non-brewing yeasts using a combination of PCR and RFLP.

In order to differentiate brewing from non-brewing yeasts, a specific polymerase chain reaction (PCR) which targeted the open reading frame of FLO1 was employed. Non-brewing yeasts include 'non-brewing Saccharomyces yeasts' and 'non-Saccharomyces yeasts'. The molecular sizes of the PCR products differed between brewing and non-brewing Saccharomyces yeasts. No FLO1 PCR products were obtained from non-Saccharomyces yeasts. Specific PCR, using oligonucleotide primers that targeted the region between the 5S and 26S rRNA genes, could be used to differentiate brewing yeasts from some non-brewing yeasts. These PCR products were digested with restriction enzymes, Scr FI and Msp I. Different restriction profiles were obtained from brewing and non-brewing yeasts which could not be differentiated using specific PCR of rDNA. These results suggest that it is possible to identify brewing from non-brewing yeasts using specific PCR of FLO1 and rDNA, and detection of restriction fragment polymorphism of rDNA.

Beer↗
PubMed1993

Identification and functional analysis of chaperonin 10, the groES homolog from yeast mitochondria.

Chaperonin 60 (cpn60) and chaperonin 10 (cpn10) constitute the chaperonin system in prokaryotes, mitochondria, and chloroplasts. In Escherichia coli, these two chaperonins are also termed groEL and groES. We have used a functional assay to identify the groES homolog cpn10 in yeast mitochondria. When dimeric ribulose-1,5-bisphosphate carboxylase (Rubisco) is denatured and allowed to bind to yeast cpn60, subsequent refolding of Rubisco is strictly dependent upon yeast cpn10. The heterologous combination of cpn60 from E. coli plus yeast cpn10 is also functional. In contrast, yeast cpn60 plus E. coli cpn10 do not support refolding of Rubisco. In the presence of MgATP, yeast cpn60 and yeast cpn10 form a stable complex that can be isolated by gel filtration and that facilitates refolding of denatured Rubisco. Although the potassium-dependent ATPase activity of E. coli cpn60 can be inhibited by cpn10 from either E. coli or yeast, neither of these cpn10s inhibits the ATPase activity of yeast cpn60. Amino acid sequencing of yeast cpn10 reveals substantial similarity to the corresponding cpn10 proteins from rat mitochondria and prokaryotes.

Adenosine Triphosphatases↗
PubMed1996

Immunosuppressant target protein FKBP12 is required for P-glycoprotein function in yeast.

The mammalian P-glycoprotein (Pgp) is a approximately 170-kDa membrane protein that mediates multidrug resistance in many chemotherapy-resistant tumors by effluxing toxic compounds from the cell. Pgp homologs are expressed in many organisms, from bacteria to yeast and mammals. Previous studies established a model system to analyze the function of murine, human, and Plasmodium falciparum Pgp by heterologous expression in the yeast Saccharomyces cerevisiae. However, such studies have been hampered by the inherent resistance of yeast cells to chemotherapeutic agents. We find that an erg6 mutation, which blocks the final synthetic step of the membrane sterol ergosterol, renders yeast sensitive to anthracyclines and dactinomycin, clinically relevant Pgp substrates. We demonstrate that expression of the murine mdr3 gene confers dactinomycin resistance in both the erg6 mutant yeast strain and in an erg6 rad52 DNA repair mutant yeast strain. Similarly, murine mdr3 expression confers resistance to the immunosuppressants cyclosporin A (CsA) and FK506 in a CsA-FK506-sensitive vph6 mutant yeast strain. CsA and FK506 are known to partially overcome Pgp-mediated drug resistance, suggesting the targets of these drugs might regulate Pgp function. We find that both murine mdr3 and the yeast Pgp homolog STE6 function in yeast mutants lacking the CsA target proteins cyclophilin A and calcineurin. In contrast, murine mdr3 function was severely compromised in yeast mutants lacking the FK506/rapamycin target protein FKBP12. Both wild-type FKBP12 and an F43Y FKBP12 mutant with reduced prolyl isomerase activity supported mdr3 function. Our results support the model that immunosuppressants reverse multidrug resistance by competing with other Pgp substrates but reveal that inhibition of FKBP12-dependent Pgp function may also contribute to reversal of multidrug resistance by FK506 and rapamycin.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2005

Surface modifying substances that reduce apparent yeast cell hydrophobicity.

OBJECTIVE: To determine whether several topical compounds and other chemical entities are able to diminish the surface hydrophobicity of yeast cells. METHOD: Hydrophobicity of yeast cells was determined by binding styrene microspheres to the surface of untreated yeast or yeast pre-incubated with various substances with potential for cell surface modification. The degree of microsphere adherence to yeast cells was measured by flow cytometry. RESULTS: A significant reduction in cell surface hydrophobicity was observed when yeast was incubated in protein-containing media. Other compounds that effectively reduced microsphere binding were various formulations of K-Y and heparin. Divalent cations (Ca+ + , Mg+ + , Zn+ + , Cu + + ) were also potent inhibitors of microsphere adherence. It was possible to remove substances contributing to microsphere binding by chemical extraction of the yeast. Yeast having reduced microsphere binding activity also showed diminished binding of concanavalin A. CONCLUSIONS: Several commercially available compounds were able to block binding of styrene microspheres to yeast. Some of the binding activity appeared to be attributable to mannose-containing surface components. These findings have implications for formulating therapeutic products that might block yeast binding to tissues.

Candida albicans↗
PubMed1987

The plant vacuolar protein, phytohemagglutinin, is transported to the vacuole of transgenic yeast.

Phytohemagglutinin (PHA), the major seed lectin of the common bean, Phaseolus vulgaris, accumulates in the parenchyma cells of the cotyledons. It has been previously shown that PHA is cotranslationally inserted into the endoplasmic reticulum with cleavage of the NH2-terminal signal peptide. Two N-linked oligosaccharide side chains are added, one of which is modified to a complex type in the Golgi apparatus. PHA is then deposited in membrane-bound protein storage vacuoles which are biochemically and functionally equivalent to the vacuoles of yeast cells and the lysosomes of animal cells. We wished to determine whether yeast cells would recognize the vacuolar sorting determinant of PHA and target the protein to the yeast vacuole. We have expressed the gene for leukoagglutinating PHA (PHA-L) in yeast under control of the yeast acid phosphatase (PHO5) promoter. Under control of this promoter, PHA-L accumulates to 0.1% of the total yeast protein. PHA-L produced in yeast is glycosylated as expected for a yeast vacuolar glycoprotein. Cell fractionation studies show that PHA-L is efficiently transported to the yeast vacuole. This is the first demonstration that vacuolar targeting information is recognized between two highly divergent species. A small proportion of yeast PHA-L is secreted which may be due to inefficient recognition of the vacuolar sorting signal because of the presence of an uncleaved signal peptide on a subset of the PHA-L polypeptides. This system can now be used to identify the vacuolar sorting determinant of a plant vacuolar protein.

Biological Transport↗
PubMed2001

An analysis of nine proprietary Chinese red yeast rice dietary supplements: implications of variability in chemical profile and contents.

OBJECTIVES: Some strains of Chinese red yeast rice, when prepared by solid fermentation, produce compounds called monacolins that inhibit cholesterol production. When used as a dietary supplement to achieve and maintain healthy cholesterol levels, Chinese red yeast rice has significant potential to reduce health care costs and contribute to public health by reducing heart disease risk in individuals with moderate elevations of circulating cholesterol levels. Whereas one proprietary strain of Chinese red yeast rice has been demonstrated to lower cholesterol levels significantly in clinical trials, other strains being sold as Chinese red yeast rice dietary supplements have not undergone similar evaluation. In order to determine whether the results of a clinical trial conducted with one strain of Chinese red yeast rice could be generalized to other preparations of Chinese red yeast rice, nine different commercially available dietary supplements were purchased tested for chemical constituents. DESIGN: Monacolins were measured by high performance liquid chromatography (HPLC) that separates the various monacolins in Chinese red yeast rice. Citrinin concentration, a toxic fermentation byproduct, was measured by radioimmunoassay. RESULTS: Total monacolin content varied from 0% to 0.58% w/w and only 1 of 9 preparations had the full complement of 10 monacolin compounds. Citrinin was found at measurable concentrations in 7 of the 9 preparations. CONCLUSIONS: The findings from clinical trials demonstrating significant and clinically relevant cholesterol reduction using a defined Chinese red yeast rice preparation containing 10 different monacolins cannot be generalized to preparations that do not contain the same levels and profile of monacolins. Standardized manufacturing practices should be established for Chinese red yeast rice sold as a dietary supplement in order ensure equivalence of content of active ingredients in preparations being sold to the public and to limit the production of unwanted byproducts of fermentation such as citrinin. In common with other botanical dietary supplements, the full potential of this product will not be realized until standards for production and labeling of Chinese red yeast rice are further developed.

Anticholesteremic Agents↗
PubMed1981

Plasmid vectors capable of transferring large DNA fragments to yeast.

We have constructed several cloning vectors which can be used in vitro packaging and yeast transformation. These plasmids have been designed for the convenient cloning of large segments of DNA and their transfer to yeast. They contain bacterial plasmid DNA sequences for replication and selection in Escherichia coli, yeast 2-microns plasmid DNA sequences or chromosomal replicators and yeast markers necessary for replication and selection in yeast, and the cohesive ends of bacteriophage lambda which allow packaging of recombinant molecules into lambda phage heads. Large fragments (22-38 kb) of Klebsiella pneumoniae and Zea mays DNA were ligated into plasmid vector pBTI-1 to make complete genome libraries. One clone from the K. pneumoniae library was amplified in E. coli and the purified DNA used to transform yeast cells. Transformation of yeast by large DNA fragments occurred at high frequencies. The recombinant plasmid was stably maintained in yeast, provided selective pressure for Leu+ transformants was maintained. The structurally complete recombinant plasmid can be recovered from yeast by transforming E. coli to ampicillin resistance. Fewer than 5% of the recovered plasmids had undergone recombination with endogenous yeast 2-microns plasmid.

Bacteriophage lambda↗
PubMed1993

Direct cloning of yeast genes from an ordered set of lambda clones in Saccharomyces cerevisiae by recombination in vivo.

We describe a technique that facilitates the isolation of yeast genes that are difficult to clone. This technique utilizes a plasmid vector that rescues lambda clones as yeast centromere plasmids. The source of these lambda clones is a set of clones whose location in the yeast genome has been determined by L. Riles et al. in 1993. The Escherichia coli-yeast shuttle plasmid carries URA3, ARS4 and CEN6, and contains DNA fragments from the lambda vector that flank the cloned yeast insert. When yeast is cotransformed with linearized plasmid and lambda clone DNA, Ura+ transformants are obtained by a recombination event between the lambda clone and the plasmid vector that generates an autonomously replicating plasmid containing the cloned yeast DNA sequences. Genes whose genetic map positions are known can easily be identified and recovered in this plasmid by testing only those lambda clones that map to the relevant region of the yeast genome for their ability to complement the mutant phenotype. This technique facilitates the isolation of yeast genes that resist cloning either because (1) they are underrepresented in yeast genomic libraries amplified in E. coli, (2) they provide phenotypes that are too marginal to allow selection of the gene by genetic complementation or (3) they provide phenotypes that are laborious to score. We demonstrate the utility of this technique by isolating three genes, GAL83, SSN2 and MAK7, each of which presents one of these problems for cloning.

Bacteriophage lambda↗
PubMed1997

Release of Candida albicans yeast antigens upon interaction with human neutrophils in vitro.

Candida albicans is the leading cause of invasive candidosis. As conventional tests do not reliably detect invasive infection, attention has turned to the detection of C. albicans antigens circulating in blood. As antigen tests for invasive candidosis could be improved if C. albicans antigens released upon phagocytosis were defined, this study was undertaken to characterise antigens released during the interaction of yeasts and human neutrophils in vitro. An enzyme immunoassay developed previously to detect what were believed to be predominantly C. albicans cytoplasmic antigens in patients with invasive candidosis was used to follow the neutrophil-mediated release of yeast antigens. Serum opsonisation enhanced antigen release, which was rapid and essentially complete by 1 h. When fresh C. albicans yeasts were added to medium from cultures of neutrophils plus yeasts or neutrophils plus latex beads, additional yeast antigens were released. Medium from neutrophils plus yeasts or from yeasts alone had similar immunoblot patterns with rabbit antibodies to a C. albicans cytoplasmic antigen preparation, with the reactive antigens generally being of higher mol. wt than the reactive antigens in the antigen mixture used for preparation of the antiserum. The two supernates also had similar immunoblot patterns with rabbit anti-C. albicans cell-wall mannan antibodies. These results suggest that yeast surface antigens are released quickly during phagocytosis by neutrophils. Detection of such yeast surface antigens, possibly together with selected yeast cytoplasmic antigens, should improve the sensitivity of C. albicans antigen assays.

Animals↗
PubMed1992

Optimization of yeast-expressed human liver cytochrome P450 3A4 catalytic activities by coexpressing NADPH-cytochrome P450 reductase and cytochrome b5.

Human liver P450 NF25 (CYP3A4) had been previously expressed in Saccharomyces cerevisiae using the inducible GAL10-CYC1 promoter and the phosphoglycerate kinase gene terminator [Renaud, J. P., Cullin, C., Pompon, D., Beaune, P. and Mansuy, D. (1990) Eur. J. Biochem. 194, 889-896]. The use of an improved expression vector [Urban, P., Cullin, C. and Pompon, D. (1990) Biochimie 72, 463-472] increased the amounts of P450 NF25 produced/culture medium by a factor of five, yielding up to 10 nmol/l. The availability of recently developed host cells that simultaneously overexpress yeast NADPH-P450 reductase and/or express human liver cytochrome b5, obtained through stable integration of the corresponding coding sequences into the yeast genome, led to biotechnological systems with much higher activities of yeast-expressed P450 NF25 and with much better ability to form P450 NF25-iron-metabolite complexes. 9-fold, 8-fold, and 30-fold rate increases were found respectively for nifedipine 1,4-oxidation, lidocaine N-deethylation and testosterone 6 beta-hydroxylation between P450 NF25-containing yeast microsomes from the basic strain and from the strain that both overexpresses yeast NADPH-P450 reductase and expresses human cytochrome b5. Even higher turnovers (15-fold, 20-fold and 50-fold rate increases) were obtained using P450 NF25-containing microsomes from the yeast just overexpressing yeast NADPH-P450 reductase in the presence of externally added, purified rabbit liver cytochrome b5. This is explained by the fact that the latter strain contained the highest level of NADPH-P450 reductase activity. It is noteworthy that for the three tested substrates, the presence of human or rabbit cytochrome b5 always showed a stimulating effect on the catalytic activities and this effect was saturable. Indeed, addition of rabbit cytochrome b5 to microsomes from a strain expressing human cytochrome b5 did not further enhance the catalytic rates. The yeast expression system was also used to study the formation of a P450-NF25-iron-metabolite complex. A P450 Fe(II)-(RNO) complex was obtained upon oxidation of N-hydroxyamphetamine, catalyzed by P450-NF25-containing yeast microsomes. In microsomes from the basic strain expressing P450 NF25, 10% of the starting P450 NF25 was transformed into this metabolite complex, whereas more than 80% of the starting P450 NF25 led to complex formation in microsomes from the strain overexpressing yeast NADPH-P450 reductase.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

High-gravity brewing: effects of nutrition on yeast composition, fermentative ability, and alcohol production.

A number of economic and product quality advantages exist in brewing when high-gravity worts of 16 to 18% dissolved solids are fermented. Above this level, production problems such as slow or stuck fermentations and poor yeast viability occur. Ethanol toxicity has been cited as the main cause, as brewers' yeasts are reported to tolerate only 7 to 9% (vol/vol) ethanol. The inhibitory effect of high osmotic pressure has also been implicated. In this report, it is demonstrated that the factor limiting the production of high levels of ethanol by brewing yeasts is actually a nutritional deficiency. When a nitrogen source, ergosterol, and oleic acid are added to worts up to 31% dissolved solids, it is possible to produce beers up to 16.2% (vol/vol) ethanol. Yeast viability remains high, and the yeasts can be repitched at least five times. Supplementation does not increase the fermentative tolerance of the yeasts to ethanol but increases the length and level of new yeast cell mass synthesis over that seen in unsupplemented wort (and therefore the period of more rapid wort attenuation). Glycogen, protein, and sterol levels in yeasts were examined, as was the importance of pitching rate, temperature, and degree of anaerobiosis. The ethanol tolerance of brewers' yeast is suggested to be no different than that of sake or distillers' yeast.

Journal Article↗
PubMed1995

Yeast succession in the Amazon fruit Parahancornia amapa as resource partitioning among Drosophila spp.

The succession of yeasts colonizing the fallen ripe amapa fruit, from Parahancornia amapa, was examined. The occupation of the substrate depended on both the competitive interactions of yeast species, such as the production of killer toxins, and the selective dispersion by the drosophilid guild of the amapa fruit. The yeast community associated with this Amazon fruit differed from those isolated from other fruits in the same forest. The physiological profile of these yeasts was mostly restricted to the assimilation of a few simple carbon sources, mainly L-sorbose, D-glycerol, DL-lactate, cellobiose, and salicin. Common fruit-associated yeasts of the genera Kloeckera and Hanseniaspora, Candida guilliermondii, and Candida krusei colonized fruits during the first three days after the fruit fell. These yeasts were dispersed and served as food for the invader Drosophila malerkotliana. The resident flies of the Drosophila willistoni group fed selectively on patches of yeasts colonizing fruits 3 to 10 days after the fruit fell. The killer toxin-producing yeasts Pichia kluyveri var. kluyveri and Candida fructus were probably involved in the exclusion of some species during the intermediate stages of fruit deterioration. An increase in pH, inhibiting toxin activity and the depletion of simple sugars, may have promoted an increase in yeast diversity in the later stages of decomposition. The yeast succession provided a patchy environment for the drosophilids sharing this ephemeral substrate.

Animals↗
PubMed2003

Yeast-derived human immunodeficiency virus type 1 p55(gag) virus-like particles activate dendritic cells (DCs) and induce perforin expression in Gag-specific CD8(+) T cells by cross-presentation of DCs.

To evaluate the immunogenicity of human immunodeficiency virus (HIV) type 1 p55(gag) virus-like particles (VLPs) released by budding from yeast spheroplasts, we have analyzed the effects of yeast VLPs on monocyte-derived dendritic cells (DCs). Yeast VLPs were efficiently incorporated into DCs via both macropinocytosis and endocytosis mediated by mannose-recognizing receptors, but not the mannose receptor. The uptake of yeast VLPs induced DC maturation and enhanced cytokine production, notably, interleukin-12 p70. We showed that yeast membrane components may contribute to DC maturation partly through Toll-like receptor 2 signaling. Thus, Gag particles encapsulated by yeast membrane may have an advantage in stimulating Gag-specific immune responses. We found that yeast VLPs, but not the control yeast membrane fraction, were able to activate both CD4(+) and CD8(+) T cells of HIV-infected individuals. We tested the effect of cross-presentation of VLP by DCs in two subjects recruited into a long-term nonprogressor-slow progressor cohort. When yeast VLP-loaded DCs of these patients were cocultured with peripheral blood mononuclear cells for 7 days, approximately one-third of the Gag-specific CD8(+) T cells were activated and became perforin positive. However, some of the Gag-specific CD8(+) T cells appeared to be lost during in vitro culture, especially in a patient with a high virus load. Our results suggest that DCs loaded with yeast VLPs can activate Gag-specific memory CD8(+) T cells to become effector cells in chronically HIV-infected individuals, but there still remain unresponsive Gag-specific T-cell populations in these patients.

Antigen Presentation↗
PubMed1995

Six human RNA polymerase subunits functionally substitute for their yeast counterparts.

To assess functional relatedness of individual components of the eukaryotic transcription apparatus, three human subunits (hsRPB5, hsRPB8, and hsRPB10) were tested for their ability to support yeast cell growth in the absence of their essential yeast homologs. Two of the three subunits, hsRPB8 and hsRPB10, supported normal yeast cell growth at moderate temperatures. A fourth human subunit, hsRPB9, is a homolog of the nonessential yeast subunit RPB9. Yeast cells lacking RPB9 are unable to grow at high and low temperatures and are defective in mRNA start site selection. We tested the ability of hsRPB9 to correct the growth and start site selection defect seen in the absence of RPB9. Expression of hsRPB9 on a high-copy-number plasmid, but not a low-copy-number plasmid, restored growth at high temperatures. Recombinant human hsRPB9 was also able to completely correct the start site selection defect seen at the CYC1 promoter in vitro as effectively as the yeast RPB9 subunit. Immunoprecipitation of the cell extracts from yeast cells containing either of the human subunits that function in place of their yeast counterparts in vivo suggested that they assemble with the complete set of yeast RNA polymerase II subunits. Overall, a total of six of the seven human subunits tested previously or in this study are able to substitute for their yeast counterparts in vivo, underscoring the remarkable similarities between the transcriptional machineries of lower and higher eukaryotes.

Amino Acid Sequence↗
PubMed1996

Identifying a species-specific region of yeast TF11B in vivo.

The general transcription factor IIB (TFIIB) is required for RNA polymerase II transcription in eukaryotes. It provides a physical link between the TATA-binding protein (TBP) and the RNA polymerase and is a component previously suggested to respond to transcriptional activators in vitro. In this report, we compare the yeast (Saccharomyces cerevisiae) and human forms of the protein in yeast cells to study their functional differences. We demonstrate that human TFIIB fails to functionally replace yeast TFIIB in yeast cells. By analyzing various human-yeast hybrid TFIIB molecules, we show that a 14-amino-acid region at the amino terminus of the first repeat of yeast TFIIB plays an important role in determining species specificity in vivo. In addition, we identify four amino acids in this region that are critical for an amphipathic helix unique to yeast TFIIB. By site-directed mutagenesis analyses we demonstrate that these four amino acids are important for yeast TFIIB's activity in vivo. Finally, we show that mutations in the species-specific region of yeast TFIIB can differentially affect the expression of genes activated by different activators in vivo. These results provide strong evidence suggesting that yeast TFIIB is involved in the process of transcriptional activation in living cells.

Amino Acid Sequence↗
PubMed2003

Transcriptional activation by estrogen receptor (ERalpha) and steroid receptor coactivator (SRC1) involves distinct mechanisms in yeast and mammalian cells.

Steroid receptors activate transcription in yeast cells via interactions with endogenous coactivators and/or basal factors. We examined the effects of mutations in the ligand binding domain on the transcriptional activity of ERalpha in yeast. Our results show that mutations in Helix 3 (K366A) and Helix 12 (M547A, L548A) disrupt transcriptional activity of ERalpha in yeast, as previously observed in mammalian cells. However, replacement of a conserved tyrosine residue in Helix 12 with alanine or aspartate (Y541A and Y541D), which renders ERalpha constitutively active in mammalian cells, had only a weak stimulatory effect on ligand-independent reporter activation by ERalpha in yeast. Two-hybrid interaction experiments revealed that a Y541A mutant expressed in yeast was capable of ligand-independent binding to a mammalian coactivator, suggesting that there is a subtle difference in how this mutant interacts with mammalian and yeast cofactors. We also show that the ligand-dependent activities of ERalpha and progesterone receptor (PR) in yeast cells were strongly enhanced by the human p160 protein steroid receptor coactivator (SRC1), but not by CREB-Binding Protein (CBP) or the p300/CBP associated factor (P/CAF). Although the SRC1 activation domains AD1 and AD2 are functional in yeast, deletion of these sequences only partially impaired SRC1 coactivator function in this organism; this is in contrast to similar experiments in mammalian cells. Thus SRC1 sequences involved in recruitment of CBP/p300 and Co-Activator-Associated Arginine Methyltransferase (CARM-1) in mammalian cells are not essential for its function in yeast, suggesting that SRC1 operates via distinct mechanisms in yeast and mammalian cells.

Histone Acetyltransferases↗
PubMed2000

Effect of cultivation mode on a bioprocess for chromium yeast biomass enrichment.

Defined cultivation media for yeast growth which contained 278.8 mM of glucose and 0.1 mM of chromium(III) added as K2Cr(SO4)2 x 12 H2O was used in batch and combined batch/fed-batch cultivation mode. In fed batch cultivation mode the rate of substrate addition remained constant during growth of yeast and corresponded to a growth rate of 0.25 h(-1). In both cases the growth and yeast activity was followed by on line measurement of optical density, pH and pO2 at 30 degrees C. At the end of the bioprocess the concentration of protein in yeast biomass was determined off line by the biuret reaction. Total and organically bound chromium was detected by ETA-AAS. Different cultivation modes affected the total cell protein concentration of yeast grown in media supplemented with chromium. In batch process the protein content represented 25.7% of dry yeast biomass, in contrast in the mixed bioprocess this value was 16.9% one the same period of time. The influence of cultivation mode on chromium uptake was seen in total chromium accumulation which reached 8.68 +/- 0.16 micromol g(-1) d.wt. in batch and 1.92 +/- 0.04 micromol of chromium g(-1) of dry yeast biomass in combined batch/fed-batch cultivation mode. The opposite was observed for organically bound chromium. The 60% of total accumulated chromium was organically bound during yeast growth in combined batch/fed-batch mode. When yeast was grown in batch mode this value attained 13.5%. Results suggested that a combined batch/fed-batch mode of cultivation was more effective over a batch system in chromium biotransformation to organically bound chromium, regardless of the lower protein ratio determined in the yeast biomass.

Biomass↗
PubMed2001

Mortality caused by experimental infection with the yeast Candida haemulonii in the adults of Ornithodoros moubata (Acarina: Argasidae).

A relatively high rate of mortality among engorged females of Ornithodoros moubata (Murray, 1877) was observed in our laboratory colony. The general aim of the study was to identify the causative agent responsible for this mortality. The diagnostic tests were performed by Yeast Identification Service (CBS-Delft, Netherlands) and the pathogen was identified as the yeast Candida haemulonii (van Uden et Kolipinski, 1962) Meyer et Yarrovi, 1978. The artificial infection study was performed by intrahaemocoelic inoculation of yeast suspension, resulting in a mortality of 37%. The maximum mortality of ticks infected per os by contaminated blood meal was 13%. Re-isolated yeast cells from haemolymph of dead and paralysed ticks were apparently identical with primary yeast cells, without loosing reproductive abilities. An occasional formation of elongated chains of yeast cells (pseudomycelium) was recorded. The majority of ticks infected in both experiments mentioned above survived and displayed no evident symptoms of the infection. The presence of yeast cells in the haemolymph of surviving ticks was not detected. The in vitro phagocytosis assay performed with FITC-labelled yeast cells showed that about 4% of tick haemocytes were phagocytically active against the pathogenic yeast cells. Thus phagocytosis seems to be a potent defence reaction against spreading and multiplying of the yeast C. haemulonii within the tick haemocoel.

Animals↗