Distribution of antigenic oligomannosyl side chains in the cell wall mannans of several strains of<Emphasis Type="Italic"> Candida tropicalis</Emphasis>

In order to clarify the distribution of antigenic oligomannosyl side chains in the cell wall mannans of the pathogenic yeast Candida tropicalis, the chemical structure of mannans isolated from four C. tropicalis strains was investigated using nuclear magnetic resonance, two-dimensional homonuclear Hartmann-Hahn (2D-HOHAHA) spectroscopy. Two-dimensional maps of the 2D-HOHAHA clearly showed the distribution of oligomannosyl side chains in the mannans. The linear side chain Manalpha1-3Manalpha1-(2Manalpha1-)(n)2Man [n> or =2] is present in the mannans from C. tropicalis IFO 0589 and IFO 1400, but not in the mannans from IFO 0199 and IFO 1647. The mannan of IFO 0589 is the only mannan with the branched side chains, Manalpha1-3[Manalpha1-6]Manalpha1-(2Manalpha1-)(n)2Man and Manalpha1-2Manalpha1-3[Manalpha1-6]Manalpha1-(2Manalpha1-)(n)2Man [n> or =2]. However, this mannan lacked the phosphate group and the beta-1,2-linked oligomannosyl side chain which are features of this group. The mannans of the C. tropicalis strains IFO 0589 and IFO 1400 possessed the side chains containing an alpha-1,3-linked mannose residue previously observed in Candida albicans.     

Detection of specificity of a new antigen in Candida tropicalis and its evaluation by taxonomic DNA analyses

Monospecific factor serum for identifying Candida tropicalis was obtained either from rabbit antiserum to heated cells of C. tropicalis M 1519 (S 96) or from antiserum to C. tropicalis IFO 1400, by adsorption with heated cells of Candida albicans serotype A, or C. albicans (A) and Candida krusei, respectively. We designated this adsorbed serum factor t serum. The monospecific factor serum reacted with 31 out of 32 strains of C. tropicalis, only when tested on heat-treated cell antigens, whereas it did not react with any of 72 strains of the six other medically important species of Candida. The morphological and physiological characteristics of the one strain of C. tropicalis that did not react with the factor t serum, designated the t- -strain, were shown to be similar to those of the type strain of C. tropicalis by most of the methods employed for identifying Candida. Therefore, cell wall mannan from the t- -strain was compared with that from several typical strains of C. tropicalis for its specificity by the precipitation reaction and also for its 1H-nuclear magnetic resonance spectrum. The results showed that these mannans are similar to each other serologically and physicochemically, suggesting that the new antigen t is not mannan. Taxonomic characterization of the t-- and several typical strains of C. tropicalis was carried out by determining the mol% G+C of their DNA and also their DNA homology. Although the mol% G+C values of four typical strains of C. tropicalis were fairly similar (35.2 to 36.2 mol% by the Tm method and 35.5 to 36.4 mol% by the HPLC method), the t- -strain had a G+C content of 44.1 (Tm) and 43.3 (HPLC) mol%. Furthermore, the DNAs of the t- -strain and the type strain of C. tropicalis showed only 18.2% relatedness. These results suggest that the antigen corresponding to serum factor t exists only in the cell wall of C. tropicalis strains, not in those of the other medically important Candida, and that the t- -strain should not be classified as C. tropicalis. In conclusion, the taxonomic value and usefulness of factor t serum is primarily for differentiating C. tropicalis from C. albicans serotype A serologically.     

甘蔗糖蜜酒精废液混菌发酵菌体蛋白的研究

本文报导利用甘蔗糖蜜酒精废液混菌发酵高质量菌体蛋白的研究,通过热带假丝酵母Ｃａｎｄｉｄａ ｔｒｏｐｉｃａｌｉｓ种合融合株Ｃｔ－３配伍其他菌株,混菌发酵时间缩短２￣４ｈ,生物量可达２０ｇ／Ｌ,粗蛋白质含量５０￣５３％,灰份≤１０％,水分为５￣８％,与Ｃｔ－３单菌发酵相比,蛋白质提高４￣６％。     

Isolation and characterization of thermotolerant Gluconobacter strains catalyzing oxidative fermentation at higher temperatures

Thermotolerant acetic acid bacteria belonging to the genus Gluconobacter were isolated from various kinds of fruits and flowers from Thailand and Japan. The screening strategy was built up to exclude Acetobacter strains by adding gluconic acid to a culture medium in the presence of 1% D-sorbitol or 1% D-mannitol. Eight strains of thermotolerant Gluconobacter were isolated and screened for D-fructose and L-sorbose production. They grew at wide range of temperatures from 10 degrees C to 37 degrees C and had average optimum growth temperature between 30-33 degrees C. All strains were able to produce L-sorbose and D-fructose at higher temperatures such as 37 degrees C. The 16S rRNA sequences analysis showed that the isolated strains were almost identical to G. frateurii with scores of 99.36-99.79%. Among these eight strains, especially strains CHM16 and CHM54 had high oxidase activity for D-mannitol and D-sorbitol, converting it to D-fructose and L-sorbose at 37 degrees C, respectively. Sugar alcohols oxidation proceeded without a lag time, but Gluconobacter frateurii IFO 3264T was unable to do such fermentation at 37 degrees C. Fermentation efficiency and fermentation rate of the strains CHM16 and CHM54 were quite high and they rapidly oxidized D-mannitol and D-sorbitol to D-fructose and L-sorbose at almost 100% within 24 h at 30 degrees C. Even oxidative fermentation of D-fructose done at 37 degrees C, the strain CHM16 still accumulated D-fructose at 80% within 24 h. The efficiency of L-sorbose fermentation by the strain CHM54 at 37 degrees C was superior to that observed at 30 degrees C. Thus, the eight strains were finally classified as thermotolerant members of G. frateurii.     

Essential Roles of Cell Surface Protein and Carbohydrate Components in Flocculation of a Brewer’s Yeast

Co-flocculation between cells of beer yeast IFO 2018, a flocculent strain, and non-flocculent strains was investigated by means of a chemical modification method. Treatment with periodate deprived non-flocculent cells, but not flocculent cells, of the ability to co-flocculate. Treatment with mercaptoethanol or photo-irradiation in the presence of methylene blue deprived flocculent cells, but not non-flocculent cells, of the co-flocculating ability. Mercaptoethanol-treated or photoirradiated flocculent cells (beer yeast IFO 2018) co-flocculated with periodate-treated flocculent cells, but periodate-treated cells subsequently subjected to mercaptoethanol treatment or photoirradiation neither flocculated by themselves nor co-flocculated with other cells. Thus, it is likely that both protein and carbohydrate components of the yeast cell surface play important roles in the mutual recognition and intercellular interaction involved in flocculation. It is strongly suggested that the essential carbohydrate which is widely distributed among Saccharomyces species is the mannan fraction on the cell wall, and that a flocculent yeast strain produces surface protein component(s) which recognize and bind the mannan component of adjacent cells.     

Characterization of thermotolerant Acetobacter pasteurianus strains and their quinoprotein alcohol dehydrogenases

We isolated several thermotolerant Acetobacter species of which MSU10 strain, identified as Acetobacter pasteurianus, could grow well on agar plates at 41°C, tolerate to 1.5% acetic acid or 4% ethanol at 39°C, similarly seen with A. pasteurianus SKU1108 previously isolated. The MSU10 strain showed higher acetic acid productivity in a medium containing 6% ethanol at 37°C than SKU1108 while SKU1108 strain could accumulate more acetic acid in a medium supplemented with 4–5% ethanol at the same temperature. The fermentation ability at 37°C of these thermotolerant strains was superior to that of mesophilic A. pasteurianus IFO3191 strain having weak growth and very delayed acetic acid production at 37°C even at 4% ethanol. Alcohol dehydrogenases (ADHs) were purified from MSU10, SKU1108, and IFO3191 strains, and their properties were compared related to the thermotolerance. ADH of the thermotolerant strains had a little higher optimal temperature and heat stability than that of mesophilic IFO3191. More critically, ADHs from MSU10 and SKU1108 strains exhibited a higher resistance to ethanol and acetic acid than IFO3191 enzyme at elevated temperature. Furthermore, in this study, the ADH genes were cloned, and the amino acid sequences of ADH subunit I, subunit II, and subunit III were compared. The difference in the amino acid residues could be seen, seemingly related to the thermotolerance, between MSU10 or SKU1108 ADH and IFO 3191 ADH.     

Immunochemical study on the mannans of Candida albicans NIH A-207, NIH B-792, and J-1012 strains prepared by fractional precipitation with cetyltrimethylammonium bromide

The mannans of Candida albicans NIH A-207 (A strain, serotype A), C. albicans NIH B-792 (B strain, serotype B), and C. albicans J-1012 (J strain, serotype C) prepared by fractional precipitation with cetyltrimethylammonium bromide (Cetavlon) were investigated for their immunochemical properties. Upon treatment with 10 mM HCl at 100 degrees C for 60 min, the mannans of A and B strains each released a mixture of manno-oligosaccharides ranging from hexaose to mannose together with (for each one) an acid-modified mannan, while J-strain mannan released lower oligosaccharides, tetraose to mannose. The acid-modified mannan of B strain did not show antibody-precipitating activity against homologous antiserum, whereas acid-modified A- and J-strain mannans retained most of this activity. The acid-released oligosaccharides were assumed to consist of beta-1,2-linked D-mannopyranosyl residues from the results of specific rotation and proton magnetic resonance studies.     

Yeast whole-cell biocatalyst constructed by intracellular overproduction of Rhizopus oryzae lipase is applicable to biodiesel fuel production

Yeast whole-cell biocatalysts for lipase-catalyzed reactions were constructed by intracellularly overproducing Rhizopus oryzae lipase (ROL) in Saccharomvces cerevisiae MT8-1. The gene encoding lipase from R. orvzae IFO4697 was cloned, and intracellular overproduction systems of a recombinant ROL with a pro-sequence (rProROL) were constructed. When rProROL from R. oryzae IFO4697 was produced under the control of the 5'-upstream region of the isocitrate lyase gene of Candida tropicalis (UPR-ICL) at 30 degrees C for 98 h by two-stage cultivation using SDC medium (SD medium with 2% casamino acids) containing 2.0% and 0.5% glucose, intracellular lipase activity reached levels up to 474.5 IU/l. These whole-cell biocatalysts were permeabilized by air-drying and used for the synthesis of methyl esters (MEs), a potential biodiesel fuel, from plant oil and methanol in a solvent-free and water-containing system. The ME content in the reaction mixture was 71 wt% after a 165-h reaction at 37 degrres C with stepwise addition of methanol. These results indicate that an efficient whole-cell biocatalyst can be prepared by intracellular overproduction of lipase in yeast cells and their permeabilization.     

Acetolysis of Pichia pastoris IFO 0948 strain mannan containing alpha-1,2 and beta-1,2 linkages using acetolysis medium of low sulfuric acid concentration

To obtain manno-oligosaccharides containing beta-1,2-linked nonreducing terminal groups from the mannan of Pichia pastoris IFO 0948 strain by acetolysis, an attempt was made to establish the reaction conditions under which cleavage of the alpha-1,6 linkage took place preferentially leaving manno-oligosaccharides composed largely of beta-1,2 linkages. By the action of an ordinary acetolysis medium, a 10/10/1 (v/v) mixture of acetic anhydride, acetic acid, and sulfuric acid at 40 degrees C for 13 h or at 25 degrees C for 120 h, the O-acetyl derivative of this mannan gave mannose, mannobiose, mannotriose, and mannopentaose. However, treatment of the same O-acetyl mannan with a 50/50/1 (v/v) acetolysis medium at 40 degrees C for 15 h gave a mannotetraose in addition to mannose, mannobiose, mannotriose, and mannopentaose. Use of a 100/100/1 (v/v) acetolysis medium at 40 degrees C for 36 h gave a more satisfactory result, a mixture of oligosaccharides, from mannose to mannopentaose, which contained more mannotetraose than mannopentaose. Because both mannotetraose and mannopentaose contained alpha-1,2 and beta-1,2 linkages, it was concluded that an acetolysis medium containing a low concentration of sulfuric acid, up to 0.5% (v/v), facilitates the preferential cleavage of the alpha-1,6 linkage, leaving manno-oligosaccharides containing the beta-1,2 linkage which was found to be labile to the action of the 10/10/1 (v/v) acetolysis medium.     

Cellular characterisation of Candida tropicalis presenting fluconazole-related trailing growth

We assessed fluconazole susceptibility in 52 Candida tropicalis clinical strains using seven antifungal susceptibility methods, including broth microdilution (BMD) [standard M27 A3 (with neutral and acid pH), ATB Fungus 3, Vitek 2 system and flow cytometric analysis] and agar-based methods (disk diffusion and E-test). Trailing growth, detection of cell-associated secreted aspartic proteases (Saps) and morphological and ultrastructural traits of these clinical strains were also examined. The ranges of fluconazole 24 h-minimum inhibitory concentration (MIC) values were similar among all methods. The essential agreement among the methods used for MIC determinations was excellent and all methods categorised all strains as susceptible, except for one strain that showed a minor error. The presence of the trailing effect was assessed by six methods. Trailing positivity was observed for 86.5-100% of the strains. The exception was the BMD-Ac method where trailing growth was not observed. Morphological and ultrastructural alterations were detected in C. tropicalis trailing cells, including mitochondrial swelling and cell walls with irregular shapes. We tested the production of Saps in 13 C. tropicalis strains expressing trailing growth through flow cytometry. Our results showed that all of the C. tropicalis strains up-regulated surface Sap expression after 24 h or 48 h of exposure to fluconazole, which was not observed in untreated yeast strains. We concluded that C. tropicalis strains expressing trailing growth presented some particular features on both biological and ultrastructural levels.     

Susceptibility of three different strains of juvenile Atlantic halibut (Hippoglossus hippoglossus L.) cultured at two different temperatures to Vibrio anguillarum and temperature effect on antibody response

Three geographically distinct-reared strains (Canadian, Icelandic, Norwegian) of juvenile Atlantic halibut (Hippoglossus hippoglossus L.) cultured at optimal and super-optimal growth temperatures (12 and 18 degrees C respectively), were challenged with a virulent isolate of Vibrio anguillarum by injection. The halibut were injected intraperitoneally with 100 microl of the bacterial suspension (1 x 10(6) cells per fish). After challenge, temperature and strain-related differences in survival were observed. Canadian and Icelandic halibut cultured at the super-optimal temperature of 18 degrees C were significantly more susceptible to infection than those strains cultured at 12 degrees C. Total mortality at 18 degrees C for the Canadian and Icelandic strains was 56.4 and 61.85% respectively, compared to 32 and 26.6% respectively at 12 degrees C. Norwegian halibut were significantly more resistant to infection with V. anguillarum at 18 degrees C compared to the other strains, with total mortality of 13.3%. There was no significant difference in total mortality of Norwegian halibut at 18 or 12 degrees C (13.3, 25% respectively). The specificity of the antibodies in sera from challenged halibut cultured at 18 degrees C was primarily to LPS. Immunoblots showed the presence of antibodies against O-side chain antigens. This reaction was strongest in sera from the Norwegian halibut strain compared with the Canadian and Icelandic halibut, which suggests that the difference in resistance to challenge may be ascribable to the presence of antibodies to LPS. Specific antibody levels, as measured by ELISA, increased with increasing temperature and strain differences were apparent, however these did not relate to disease resistance.     

提高产抗生素链霉菌紫外诱变正变率的研究

将UV诱变了的产抗生素链霉菌（Streptomyces sp.）AP 19-1菌株之孢子,置于适宜的生长温度27℃与接近抑制生长的胁迫温度33℃下培养,结果表明：在33℃下生长获得的子代菌株中,产抗生素水平超过其出发菌株的正向突变体所占的比例,明显比在27℃下培养的高。27℃下培养,正向突变体占总子代菌株数的25.8%,而在33℃下培养则为58.1%。用17种随机引物对出发菌株与UV诱变子代菌株进行总DNA的RAPD测验证明,在接近抑制生长的温度33℃下培养获得的子代,发生在其DNA水平上的变异程度比在27℃的要高得多。这一方法能较大幅度提高链霉菌紫外诱变育种的工作效率,同时也为链霉菌经紫外诱变后突变形成机制的进一步研究提供了新途径。Abstract: UV irradiated spores of Streptomyces sp. AP 19 -1 strain that can produce antibiotics were incubated at 27 ℃, and 33 ℃ which is close to inhibiting growth temperature, respectively. The results showed that there were much more forward mutants, whose level of producing antibiotics is higher than that of original strain, among the offspring of UV irradiated spores grown at 33 ℃, compared to that grown at 27 ℃. The percentage of the forward mutants was 25.8 % at 27 ℃ and 58.1% at 33 ℃. The progeny strains and the original strain were tested by RAPD using total DNA with 17 primers. It was demonstrated that more variations occurred in the chromosomal DNA of the progeny strains grown at 33 ℃ than in that at 27 ℃. This method facilitates increasing the efficiency of induced mutagenesis in breeding and provides a new way to study the mechanisms of mutation formation in UV irradiated Streptomyces sp. cells.     

The attachment to, and invasion of HeLa cells by Salmonella typhimurium: the contribution of mannose-sensitive and mannose-resistant haemagglutinating activities

The association of the haemagglutinating activities of Salmonella typhimurium cultures with bacterial adhesion to HeLa cells, and the internalization of the bacteria by HeLa cells, was studied. Adhesion was not inhibited by alpha-methyl-D-mannoside (i.e. adhesion was mannose-resistant), and only four of the six strains tested produced type 1 fimbriae and the associated mannose-sensitive haemagglutinin (MSHA). The other two strains belonged to the non-fimbriate FIRN biogroup. Cultures of all six strains contained a mannose-resistant haemagglutinating (MRHA) activity when grown at 37 degrees C, but cultures of only one fimbriate and one non-fimbriate strain did so when grown at 18 degrees C. From the comparison of cultures grown at 18 degrees C and 37 degrees C, and of mutant strains with the phenotypes MRHA-negative/MSHA-positive, or MRHA-positive/MSHA-negative, it was concluded that the MRHA activity was responsible for the attachment of salmonellae to HeLa cells. Only bacterial adhesion that was resistant to mannose resulted in the internalization of the bacteria by the HeLa cells.     

Phylogenetic identification of n-alkane assimilating Candida yeasts based on nucleotide divergence in the 59 end of LSU rDNA gene

Phylogenetic relationships of several species within the n-alkane assimilating Candida yeasts were investigated by using characters from the nucleotide sequence of the variable D1/D2 region at the 5' end of a large-subunit (26S) ribosomal DNA (rDNA) gene. First the nucleotide sequences of D1/D2 domain of Candida sp. 1098 (formerly identified as C. tropicalis 1098) and its dicarboxylic acid-producing-mutant strain M1210 were investigated. These two nucleotide sequences were identical and lacked only one base pair compared with that of C. maltosa CBS 5611 (type strain), and they were identified as C. maltosa. We then showed that C. maltosa IFO 1978 (formerly identified as C. cloacae) and C. maltosa IFO 1975 (formerly identified as C. subtropicalis) had the same nucleotide sequence and had only one base pair substitution compared with C. maltosa CBS 5611 (type strain), which is consistent with conventional classification. We also found that another widely studied n-alkane assimilating Candida yeast, C. tropicalis pk233, to be C. viswanathii.     

Influence of elevated temperature on starch hydrolysis by enterotoxin-positive and enterotoxin-negative strains of Clostridium perfringens type A.

Enterotoxin-positive (Ent+) and enterotoxin-negative (Ent-) strains of Clostridium perfringens were cultured in Duncan-Strong sporulation medium containing starch at 37 and 46 degrees C. At 37 degrees C, all strains degraded starch and sporulated well. However, only Ent- strains could hydrolyze starch, grow extensively, and sporulate at 46 degrees C. Growth, sporulation, and starch hydrolysis by Ent+ strains at 46 degrees C were equivalent to those obtained at 37 degrees C when alpha-amylase was added to the cultures during growth. The total amount of extracellular plus intracellular amylase in cultures of Ent+ strains was significantly less in cells incubated at 46 degrees C than in cells incubated at 37 degrees C. These results contradict an earlier report that Ent+ strains cannot sporulate well near their optimal growth temperature (R. G. Labbe and C. L. Duncan, Can. J. Microbiol. 20:1493-1501, 1974) and suggest that synthesis of alpha-amylase in Ent+ strains is regulated by temperature.     

Influence of elevated temperature on starch hydrolysis by enterotoxin-positive and enterotoxin-negative strains of Clostridium perfringens type A.

Enterotoxin-positive (Ent+) and enterotoxin-negative (Ent-) strains of Clostridium perfringens were cultured in Duncan-Strong sporulation medium containing starch at 37 and 46 degrees C. At 37 degrees C, all strains degraded starch and sporulated well. However, only Ent- strains could hydrolyze starch, grow extensively, and sporulate at 46 degrees C. Growth, sporulation, and starch hydrolysis by Ent+ strains at 46 degrees C were equivalent to those obtained at 37 degrees C when alpha-amylase was added to the cultures during growth. The total amount of extracellular plus intracellular amylase in cultures of Ent+ strains was significantly less in cells incubated at 46 degrees C than in cells incubated at 37 degrees C. These results contradict an earlier report that Ent+ strains cannot sporulate well near their optimal growth temperature (R. G. Labbe and C. L. Duncan, Can. J. Microbiol. 20:1493-1501, 1974) and suggest that synthesis of alpha-amylase in Ent+ strains is regulated by temperature.     

Protein Arp and protein H from group A streptococci. Ig binding and dimerization are regulated by temperature.

Cell surface proteins that bind to the Fc part of Ig are expressed by many strains of group A streptococci, an important human pathogen. Two such bacterial strains, AP4 and AP1, were shown to bind IgA and IgG, respectively, in a temperature-dependent manner. The binding of radiolabeled Ig to the bacterial cells was lower at 37 degrees C than at 22 and 4 degrees C. Similarly, protein Arp, the IgA-binding protein isolated from strain AP4, and protein H, the IgG-binding protein isolated from strain AP1, displayed a strong Ig-binding at 22 degrees C and lower temperatures, and virtually no binding at all at 37 degrees C. The effect was reversible: lowering of the temperature restored the binding and vice versa. A gradual shift between binding and nonbinding took place between 27 and 37 degrees C. Gel chromatography and velocity sedimentation centrifugation showed that protein Arp and protein H appeared as noncovalently associated dimers at 10 and 22 degrees C, and as monomers at 37 degrees C. These results strongly suggest that the dimerization of protein Arp and protein H, rather than the low temperature itself, yielded the strong Ig-binding of the proteins at 10 and 22 degrees C. Indeed, after covalent cross-linking of the dimers at 10 degrees C by incubation with low concentrations of glutaraldehyde, full Ig-binding was achieved even at 37 degrees C. A carboxyl-terminal proteolytic fragment of protein Arp, which completely lacked the IgA-binding capacity at any temperature, showed the same temperature-dependent dimerization as intact protein Arp, suggesting that the Ig-binding part of the protein is not required for dimerization. The implications of these results for the function of Ig-binding group A streptococcal proteins, and their role in the host-parasite relationship are discussed.     

Polymorphism of Sporothrix schenckii surface polysaccharides as a function of morphological differentiation.

The alkali-extractable polysaccharides from different morphological types of two Sporothrix schenckii strains (1099.12 and 1099.18) were investigated. Dissociation of morphological phase transition and temperature effects was possible in a synthetic medium which produced cultures with 100% yeast forms either at 25 or at 37 degrees C. Only rhamnomannans with single-unit alpha-L-rhamnopyranosyl side chains were formed by the yeast forms irrespective of the incubation temperature. The higher temperature inhibited formation of 4-O- and 2,4-di-O-substituted alpha-D-mannopyranose units in the rhamnomannan. An apparently unsporulated mycelium culture of one S. schenckii strain (1099.12) synthesized a galactomannan whose structure was partially determined by methylation analysis and by proton and 13C nuclear magnetic resonance spectroscopy. In another strain (1099.18), a mannan was excreted in the medium of an apparently conidia-less mycelial form at 25 degrees C with short incubation. Its structure was also partially determined. An apparent mixture of this mannan and a rhamnomannan rich in alpha-L-rhamnopyranosyl-(1 leads to 2)-alpha-L-rhamnopyranose side chains formed in these cultures on prolonged incubation. The proportion of the excreted rhamnomannan increased as the mycelium sporulated and conidia were more numerous. Mannans or galactomannans may be transient polysaccharides in the young mycelium of S. schenckii. As the culture develops, rhamnomannans are formed in amounts usually masking the presence of other mannose-containing polysaccharides. It is suggested that in S. schenckii different polysaccharides are formed with side chains containing different proportions of rhamnose, mannose, or galactose, as a function of morphological differentiation.     

Comparison of Saccharomyces cerevisiae strains of clinical and nonclinical origin by molecular typing and determination of putative virulence traits

Saccharomyces cerevisiae strains of clinical and nonclinical origin were compared by pulse field gel electrophoresis. Complete separation between strains of clinical origin and food strains by their chromosome length polymorphism was not obtained even though there was a tendency for the clinical and food strains to cluster separately. All the investigated strains, except for one food strain, were able to grow at temperatures > or =37 degrees C but not at 42 degrees C. Great strain variations were observed in pseudohyphal growth and invasiveness, but the characters were not linked to strains of clinical origin. The adhesion capacities of the yeast strains to a human intestinal epithelial cell line (Caco-2) in response to different nutritional availabilities were determined, as were the effects of the strains on the transepithelial electrical resistance (TER) across polarized monolayers of Caco-2 cells. The yeast strains displayed very low adhesion capacities to Caco-2 cells (0.6-6.2%), and no significant difference was observed between the strains of clinical and nonclinical origin. Both S. cerevisiae strains of clinical and non-clinical origin increased the TER of polarized monolayers of Caco-2 cells. Based on the results obtained in this study, no specific virulence factor was found that clearly separated the strains of clinical origin from the strains of nonclinical origin. On the contrary, all investigated strains of S. cerevisiae were found to strengthen the epithelial barrier function.     

Correlation between polyploidy and auxotrophic segregation in the imperfect yeast Candida albicans.

In order to clarify the relationship between polyploidization and the capability of phenotypic switching in the imperfect yeast Candida albicans, two types of variants were isolated as segregants from a fusant, which produced a proportion of the cell population with a higher ploidy than the rest, either in a temperature-dependent or -independent manner, when incubated at low (28 degrees C) and high (37 degrees C) temperatures. In the case of the temperature-dependent type of variants, high-ploidy cells appeared at 37 degrees C but rarely at 28 degrees C. This phenotype was named Pldts (temperature-sensitive polyploidization), and the temperature-independent phenotype was called Pld-. The appearance of high-ploidy cells in the culture of the Pldts strain at 37 degrees C was accompanied by a significant increase in the frequency of auxotrophic variants; these variants probably occur as a result of segregation of auxotrophic markers from the heterozygous to the homozygous state. Both Pldts and Pld- phenotypes were recessive in a fusion with a Pld+ parent. An adenine auxotrophic marker (ade1) was introduced into a Pldts strain in a heterozygous state, and the individual high-ploidy cells of this strain, grown at 37 degrees C, were micromanipulated to form colonies, which consisted of red and white sectors appearing at high frequency on a pink background. When the ade1 auxotrophy was introduced into Pld- strains, frequently sectored colonies were produced. These results suggested an increased level of chromosome missegregation in both types of Pld mutants. Analyses by pulsed-field gel electrophoresis of Ade-segregants, derived from a micromanipulated high-ploidy cell of a Pld(ts) strain, suggested the occurrence of nonreciprocal recombination, some of which includes chromosome loss.