Population changes of indigenous murine Candida pintolopesii under various experimental conditions and routes of inoculation.

Fecal Candida pintolopesii population levels were found to be significantly affected by laparotomy-inoculation-Bollman apparatus restraint, laparotomy-inoculation, and a milk diet. Gastrectomized rats could not support yeast populations; in intact animals, yeast cells failed to colonize the gastrointestinal tract distal to the stomach. Copraphagia contributed little to stomach yeast populations, supporting the notion that stomach yeast growth occurs at fairly rapid rates.     

Gastric Infection with Kazachstania heterogenica Influences the Outcome of a Helicobacter suis Infection in Mongolian Gerbils

Background:  The Mongolian gerbil model is often used to investigate the interactions between different gastric Helicobacter species and the gastric tissue. A preliminary screening of a gerbil population intended for use in Helicobacter suis infection studies revealed a natural yeast infection in the stomach of these animals. After identification, we have investigated the effect of the gastric yeast infection on the outcome of an experimental H. suis infection in Mongolian gerbils.
Materials and methods:  Yeast cells were isolated from the stomachs of Mongolian gerbils. Identification was done by Internally Transcribed rRNA Spacer 2 Region PCR fragment length analysis. To investigate a possible pathologic role of this yeast, Mongolian gerbils were infected experimentally with this yeast. Co-infection with the newly isolated H. suis was performed to investigate possible interactions between both micro-organisms.
Results:  Kazachstania heterogenica was found colonizing the stomach of Mongolian gerbils, mainly in the antrum. Few pathologic changes were seen in the stomachs of infected animals. Experimental co-infection of gerbils with this yeast and the newly isolated H. suis showed a significant increase in inflammation in animals infected with both micro-organisms compared to animals infected only with H. suis .
Conclusions:  K. heterogenica colonizes the stomach of Mongolian gerbils in exactly the same regions as gastric Helicobacter species. The uncontrolled presence of this yeast in the gerbil stomach can lead to an overestimation of the inflammation caused by Helicobacter in this animal model.     

Genetic analysis of the gastric precancer-cancer system. I. Research in different populations

Heredity predisposition was analysed in cancer and precancer stomach diseases in distinct populations. Some phenotypic and genetic characters of the stomach "precancer--cancer" system were studied. Similarity in the degree of stomach cancer inheritance, its segregation frequency and recurrent risk was revealed for populations. However, the degree of correlation between cancer and precancer stomach disease was different in distinct populations, this being more pronounced in "cancer--gastric ulcer" system.     

Cyniclomyces guttulatus (Saccharomycopsis guttulata) — culture,ultrastructure and physiology

Organisms that form an essential extra inner lining of selected areas of the stomach mucosa occur in mice, rats and some other animals. The yeast Cyniclomyces guttulatus (Saccharomycopsis guttulata) was shown in this study to line the stomach of domestic and feral rabbits, guinea pigs, and chinchillas. The layer of yeast cells formed a loose barrier between lumen contents and mucosal surface. A rapid rate of multiplication in the stomach provided yeast cells that blended in with stomach lumen contents, passed throught the gut, and were finally excreted in large numbers in fecal pellets. Ascospore formation occurred during passage through the large intestine. The layer of yeast cells lining the stomach had no evident salubrious nor deleterious effect on the animal. C. guttulatus grew rapidly from stomach contents or single fecal pellets in a new enriched semisolid medium. Growth was good at pH 1 through 8 on the solidified enriched medium. A very unusual characteristic of C. guttulatus is optimal growht at 38° C, and growth at 42° C, with failure to grow below 30° C. TEM demonstrated a very thick, laminated cell wall which had a thick, filamentous external coating. There were mitochondria, polyribosomes, lipid droplets, and an unusually large central nucleus. The developing spore nucleus became extremely electron dense and encapsulated, along with condensed mitochondria, ribosomes, short membrane sections and other organelles, in a dense lamellar covering.     

A yeast in the stomach of the mouse

Summary The high incidence (100 %) ofTorulopsis pintolopesi in the stomach of the mouse and the absence of any type of inflammatory response show the existance of an adaptation between the yeast and the mouse. This is in agreement with the opinion ofParle that the yeast belongs to the normal flora of the digestive tract. According to our studiesT. pintolopesi is an acidophilic species which is a normal host in the stomach and a transient organism in the intestine.     

High degree of correlation between molecular polymorphism and geographic origin of wine yeast strains

AIMS: To guarantee the endemic genetic background of the isolates obtained in yeast isolation programs, it is necessary to differentiate between endemic and commercial strains because the progressive use of commercial yeast in wine areas around the world would affect the autochthonous yeast populations. METHODS AND RESULTS: Mitochondrial DNA restriction analysis, electrophoretic karyotyping and random amplification of polymorphic DNA (RAPD) were evaluated as experimental approaches to correlate genomic polymorphism and geographic origin of native wine yeast strains. The three molecular methods were capable of detecting a European commercial strain among native Chilean strains; however, RAPD proved to have the best performance. CONCLUSIONS: The molecular polymorphism analysis is useful to evaluate the geographical origin of native yeast isolates and confirms or refutes the genetic background of currently marketed strains. SIGNIFICANCE AND IMPACT OF THE STUDY: This study permits a genetic characterization of native yeast populations and confirms its utility as a tool for evaluating if a native isolate derives from the region where it was collected, permitting, furthermore, to develop studies on the evolution of native yeast populations and to evaluate the effect of introduced yeasts on these populations.     

Variable adhesion and diurnal population patterns of epiphytic yeasts on creeping bentgrass

Irrigation and an in vitro agitation assay were used to determine the percentage of the epiphytic yeast community (Cryptococcus, Pseudozyma, Rhodotorula, and Sporobolomyces) adhering to the phylloplane of creeping bentgrass (Agrostis palustris (Huds.) Pers.). Colony-forming units (cfu) of total epiphytic yeast populations (adherent and nonadherent cells) and of adherent populations (cells not removed by agitation) were determined by leaf washing and dilution plating. In an in vitro assay, 40.0% and 57.1% of the yeast adhered to the leaves, whereas, in initial field trials the percentage of adherent yeasts ranged from 40.0% to 71.9% of the total population. Adherent yeast cfu on leaves in the morning were significantly lower on bentgrass (8.0 x 103 to 3.1 x 104 cfu.cm(-2)) compared with total yeast cfu (1.4 x 104 to 4.7 x 104 cfu.cm(-2)) on the nonirrigated control. No differences in yeast populations were observed between irrigated and nonirrigated plots 2 h after the 0900 treatments. Yeast populations followed a diurnal pattern, with larger cfu recovered from bentgrass leaves in the morning and significantly lower populations recovered in the afternoon. At 1400 the adherent yeast were 83.1%-100% of the total yeast population recovered from the leaves. The relative adhesiveness of the epiphytic yeast community on bentgrass leaves is dynamic with nonadherent cells making up a larger percentage of the population in the mornings than the afternoons.     

Morphologically-structured models of growing budding yeast populations

It has been well recognized that many key aspects of cell cycle regulation are encoded into the size distributions of growing budding yeast populations due to the tight coupling between cell growth and cell division present in this organism. Several attempts have been made to model the cell size distribution of growing yeast populations in order to obtain insight on the underlying control mechanisms, but most were based on the age structure of asymmetrically dividing populations. Here we propose a new framework that couples a morphologically-structured representation of the population with population balance theory to formulate a dynamic model for the size distribution of growing yeast populations. An advantage of the presented framework is that it allows derivation of simpler models that are directly identifiable from experiments. We show how such models can be derived from the general framework and demonstrate their utility in analyzing yeast population data. Finally, by employing a recently proposed numerical scheme, we proceed to integrate numerically the full distributed model to provide predictions of dynamics of the cell size structure of growing yeast populations.     

An analysis of resource allocation in response to dietary yeast in Drosophila melanogaster

Drosophila melanogaster exhibit an increase in fecundity and a decrease in length of life and starvation resistance when the diet is enriched through the addition of live yeast. It has been proposed that this represents a necessary energetic trade-off between reproductive and somatic functions. We examined the metabolic aspects of this trade-off. We measured egg production, dry wt, somatic lipid and carbohydrate storage, and metabolic rate in response to changing amounts of live dietary yeast. These variables were measured in five replicate populations selected for postponed aging and five replicate short lived control populations. We find that all ten populations show an overall increase in egg production and decrease in the amount of stored metabolites in the presence of increasing amounts of yeast. All populations increase metabolic rate in response to increasing amounts of live dietary yeast. The energetics of this phenomenon suggest that increased egg production results from increased acquisition of nutrients available in yeast with only a small redirection of resources from storage to egg production.     

Molecular polymorphism distribution in phenotypically distinct populations of wine yeast strains.

Electrophoretic karyotyping and mitochondrial DNA restriction analysis were used to analyze natural yeast populations from fermenting musts in El Penedès, Spain. Both analyses revealed a considerable degree of polymorphism, indicating heterogeneous natural populations. By specifically designed genetic selection protocols, strains showing potentially interesting phenotypes, such as high tolerance to ethanol and temperature or the ability to grow and to ferment in wine-water-sugar mixtures, were isolated from these natural populations. Genetic analysis showed a strong correlation between the selected phenotypes and mitochondrial DNA polymorphisms. Karyotype analysis revealed several genetically similar yeast lineages in the natural yeast microflora, which we interpret as genetically isolated subpopulations of yeast strains with distinct genetic traits, which may correspond to specific microenvironments. Thus, molecular polymorphism analysis may be useful not only to study the geographical distribution of natural yeast strains but also to identify strains with specific phenotypic properties.     

Ethanol tolerance and the variation of plasma membrane composition of yeast floc populations with different size distribution

The ethanol tolerance of a self-flocculating yeast strain SPSC01 was investigated in an oxygen-limited fed-batch bioreactor. Employing Focused Beam Reflectance Measurement (FBRM) on-line monitoring system, four yeast floc populations with the average size ranging from 100 to 400mum were obtained. It was found that ethanol tolerance increased with the increasing floc size in the 100, 200, and 300mum floc populations, while increasing the average floc size further to 400mum resulted in lower ethanol tolerance. Examination of the membrane composition of different floc populations revealed that the plasma membrane composition of the floc populations was significantly different in the contents of ergosterol, phosphatidylinositol, as well as phospholipid palmitoleic acid. What's more, the plasma membrane of more ethanol tolerant floc population was less permeable when subjected to 15% (v/v) ethanol shock treatment, and the plasma membrane ATPase activities were higher in the floc populations with higher ethanol tolerance. These results indicate that the average size distribution of the floc populations exerted great influence on the physiological status of yeast cells during the ethanol production process, leading to the changes in plasma membrane composition that contributed to improved ethanol tolerance in self-flocculating yeast SPSC01.     

The dynamics of the yeast community of the Tagus river estuary: testing the hypothesis of the multiple origins of estuarine yeasts

Yeasts are common inhabitants of different types of aquatic habitats, including marine and estuarine waters and rivers. Although numerous studies have surveyed yeast occurrence in these habitats, the identification of autochthonous populations has been problematic because several yeast species seem to be very versatile and therefore mere presence is not sufficient to establish an ecological association. In the present study we investigated the dynamics of the yeast community in the Tagus river estuary (Portugal) by combining a microbiological study involving isolation, quantification, and molecular identification of dominant yeast populations with the analysis of hydrological and hydrographical data. We set out to test the hypothesis of the multiple origins of estuarine yeast populations in a transect of the Tagus estuary and we postulate four possible sources: open sea, terrestrial, gastrointestinal and the estuary itself in the case of populations that have become resident. Candida parapsilosis and Pichia guilliermondii were correlated with Escherichia coli, which indicated an intestinal origin. Other cream-colored yeasts like Debaryomyces hansenii and Candida zeylanoides had similar dynamics, but no association with E. coli and quite distinct ecological preferences. They might represent a group of resident estuarine populations whose primary origin is diverse and can include marine, terrestrial, and gastrointestinal habitats. Another major yeast population was represented by Rhodotorula mucilaginosa. The cosmopolitan nature of that species and its moderate association with E. coli point to terrestrial sources as primary habitats.     

Protective effects of oral administration of yeast thioredoxin against gastric mucosal injury

Thioredoxin (TRX) is a redox regulating protein which has protective effects against oxidative stress-induced damage to cells and tissues. In this study, we investigated the effects of orally administered TRX derived from edible yeast, Saccharomyces cerevisiae, on gastric mucosa. First, we examined the digestibility of orally administered yeast TRX in mice, and detected yeast TRX in the stomach for 4?h after administration. Next, we investigated the mitigation of gastric mucosal injury after the oral administration of yeast TRX in water-immersion restraint stress and HCl/ethanol-induced gastric ulcer models. Furthermore, we conducted DNA microarray analysis, using the HCl/ethanol-induced model, which revealed that several groups of genes related to tissue repair were upregulated in ulcer regions in the stomachs of rats administered with yeast TRX. These results demonstrated the viability of the use of oral administrations of yeast TRX to protect the gastric mucosa.     

Effects of different protein concentrations on longevity and feeding behavior of two adult populations of Ceratitis capitata Wiedemann (Diptera: Tephritidae)

The effects of protein intake on two adult male and female populations of Ceratitis capitata Wiedemann were assessed. One population consisted of flies reared for twenty years in the laboratory (Lab-pop); the other population consisted both of flies reared in the laboratory for approximately fifteen years and of the periodically introduced wild flies (Hybrid-pop). Three diets were tested: a no-yeast diet and two diets containing yeast (protein source) at the concentrations 6.5 g or 1.5 g per 100 ml diet. The parameters analyzed were: adult longevity, diet intake with and without yeast, and discrimination threshold for yeast. Protein intake increased Lab-pop adult longevity and did not affect longevity of the Hybrid-pop. Longevity in each population was similar for males and females fed on the same diet. Food behavior were similar for male and female adults of both populations; all preferred diets containing protein (yeast). Males and females in both populations ingested similar amounts of each diet. The discrimination threshold for yeast was similar for all males (0.5 g yeast/100 ml diet); Lab-pop females were able to detect the presence of smaller quantities of yeast in their diet, thus having a higher discrimination capacity (0.4 g/100 ml diet) as compared to the Hybrid-pop females (0.6 g/ 100 ml diet).     

The effects of fungicides on the phylloplane yeast populations of creeping bentgrass

The effects of fungicides on population size and the development of fungicide resistance in the phylloplane yeast flora of bentgrass was investigated. In the spring of 2001, azoxystrobin, chlorothalonil, flutolanil, and propiconazole were applied separately over a 6-week period to creeping bentgrass (Agrostis palustris Huds.). Total and fungicide-resistant yeast populations were assessed by dilution plating onto either potato dextrose agar or potato dextrose agar amended with the test fungicides. Total yeast populations in the fungicide-treated plots were significantly lower than the check plots on three out of four sample dates. In the fall, azoxystrobin or propiconazole were applied twice to the bentgrass over 3 weeks. Significantly larger total yeast populations were observed compared with resistant or highly resistant populations for each treatment on every sample date. Total yeast populations were significantly higher in the check plots compared with either the propiconazole- or azoxystrobin-treated plots on the first three of five sample dates. A collection of yeasts (N = 114) with no prior exposure to fungicides were more sensitive to chlorothalonil, propiconazole, flutolanil, and iprodione than a second group (N = 115) isolated from fungicide-treated turfgrass. These results suggest that fungicide resistance among phylloplane yeasts is widespread and could be an important factor in the development of biological control agents for turfgrass diseases.     

Use of flow cytometry with fluorescent antibodies in real-time monitoring of simultaneously inoculated alcoholic-malolactic fermentation of Chardonnay

AIMS: To monitor in real-time the changes in microbial populations and chemistry of grape juice simultaneously inoculated with Saccharomyces cerevisiae and Oenococcus oeni. METHODS AND RESULTS: Viable populations of S. cerevisiae and O. oeni in Chardonnay fermentations were identified and quantified using fluorescent dyes and fluorescently labelled antibodies in a flow cytometric assay. Fermentation chemistry was monitored using Fourier transform infrared (FTIR) spectroscopy, except for malic acid which was measured enzymatically. Malic acid utilization by O. oeni was greatest in the presence of the yeast Cepage. Growth of O. oeni was substantially slower in the presence of the yeast VL1. The three yeasts had similar fermentation rates in the presence and absence of O. oeni. CONCLUSIONS: Viable and nonviable yeast and bacterial populations can be rapidly discriminated in simultaneous malolactic-alcoholic wine fermentations using antibodies, fluorescent dyes and flow cytometry. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first study using fluorescently labelled antibodies to discriminate and monitor yeast and bacterial populations in wine fermentations and offers a new approach to investigating microbial interactions in wine fermentations.     

Insertion of nonhomologous DNA into the yeast genome mediated by homologous recombination with a cotransforming plasmid

Bacterial plasmids containing no detectable homology with yeast DNA sequences were inserted into the yeast genome by cotransforming with a plasmid containing a yeast gene. Analysis of the yeast transformants confirmed that recombination events occurred between the prokaryotic sequences shared by the two plasmids and between the yeast sequences common to the cotransforming plasmid and to the genome. Multiple copies of the two plasmids, in both tandem and interspersed arrays, are inserted by this method. Populations of cells grown from individual transformants are heterogenous for the number of integrated sequences. The number of integrated bacterial sequences is greatly reduced after 100 generations of growth in the populations that initially contained large numbers of sequences, while it is stable in those populations that initially contained either a single or a small number of copies.     

Stability of high cell density brewery fermentations during serial repitching

The volumetric productivity of the beer fermentation process can be increased by using a higher pitching rate (i.e. higher inoculum size). However, the decreased yeast net growth observed in these high cell density brewery fermentations can adversely affect the physiological stability throughout subsequent yeast generations. Therefore, different O₂ conditions (wort aeration and yeast preoxygenation) were applied to high cell density fermentation and eight generations of fermentations were evaluated together with conventional fermentations. Freshly propagated high cell density populations adapted faster to the fermentative conditions than normal cell density populations. Preoxygenating the yeast was essential for the yeast physiological and beer flavor compound stability of high cell density fermentations during serial repitching. In contrast, the use of non-preoxygenated yeast resulted in inadequate growth which caused (1) insufficient yield of biomass to repitch all eight generations, (2) a 10% decrease in viability, (3) a moderate increase of yeast age, (4) and a dramatic increase of the unwanted flavor compounds acetaldehyde and total diacetyl during the sequence of fermentations. Therefore, to achieve sustainable high cell density fermentations throughout the economical valuable process of serial repitching, adequate yeast growth is essential.     

Possible use of Biolog methodology for monitoring yeast presence in alcoholic fermentation for wine‐making

Aims: A research was undertaken to explore the possibility to use Biolog system of microbial metabolic characterization for the monitoring of yeast population evolution during alcoholic fermentation for wine production. Methods and Results: An application of Biolog system was employed for the characterization of yeasts of oenological interest, in pure cultures and mixed consortia, in various cell concentrations. The system’s capacity to discriminate among different cell concentrations of the same yeast strain was ascertained, along with the capacity to discriminate between mixed and pure populations. Conclusions: The tested application of Biolog system resulted suitable for a quick recognition (24 h) of the presence of starter cultures within mixed populations of autochthonous yeasts. Such discrimination was confirmed with the one resulting from molecular techniques. Significance and Impact of the Study: The study suggests the possibility to employ Biolog system for an early monitoring of yeast evolution in modern wine‐making fermentations, where specialized yeasts are more and more frequently used as starters and their ability to overcome autochthonous yeast populations is crucial.     

A population study of killer viruses reveals different evolutionary histories of two closely related Saccharomyces sensu stricto yeasts

Microbes have evolved ways of interference competition to gain advantage over their ecological competitors. The use of secreted killer toxins by yeast cells through acquiring double‐stranded RNA viruses is one such prominent example. Although the killer behaviour has been well studied in laboratory yeast strains, our knowledge regarding how killer viruses are spread and maintained in nature and how yeast cells co‐evolve with viruses remains limited. We investigated these issues using a panel of 81 yeast populations belonging to three Saccharomyces sensu stricto species isolated from diverse ecological niches and geographic locations. We found that killer strains are rare among all three species. In contrast, killer toxin resistance is widespread in Saccharomyces paradoxus populations, but not in Saccharomyces cerevisiae or Saccharomyces eubayanus populations. Genetic analyses revealed that toxin resistance in S. paradoxus is often caused by dominant alleles that have independently evolved in different populations. Molecular typing identified one M28 and two types of M1 killer viruses in those killer strains. We further showed that killer viruses of the same type could lead to distinct killer phenotypes under different host backgrounds, suggesting co‐evolution between the viruses and hosts in different populations. Taken together, our data suggest that killer viruses vary in their evolutionary histories even within closely related yeast species.