Interaction of SMKT, a killer toxin produced by Pichia farinosa, with the yeast cell membranes

Potential of Non-Saccharomyces Yeasts as Probiotics and Alternatives to Antibiotics in Animal Production

Probiotics are live yeast or bacterial organisms that have beneficial effects on the host. Several microorganisms exhibit probiotic properties, the most common types being lactic acid bacteria, Bifidobacteria, spore-forming bacteria, and some yeast strains. Saccharomyces cerevisiae var. boulardii is the most important probiotic yeast species. However, another group of foodborne microorganisms, the so-called non-Saccharomyces yeasts (NSYs), has recently been re-evaluated and shown to have enormous potential in various fields of application, ranging from food fermentation to human and animal applications. NSYs are able to produce a range of bioactive compounds such as antimicrobials, mannoproteins, enzymes, polyunsaturated fatty acids, essential amino acids, vitamins, and β-glucans, which increases their potential applications as a new class of probiotics and/or alternatives to antibiotics in animal husbandry. In this review, we aim to highlight the potential and benefits of NSYs as probiotics and natural antimicrobials to improve animal health. Furthermore, the use of NSYs as biological alternatives to antibiotics to control foodborne pathogens in animal production is discussed.

Wine Barrel Biofilm as a Source of Yeasts with Non-Conventional Properties

This study investigated the main microbial groups characterizing the interior surface of oak barrels from different years (1890, 1895, 1920, 1975, 2008) used in the production of vino cotto. The yeasts were characterized for the following properties: γ-aminobutyric acid (GABA) production, antioxidant activity, air-liquid interfacial biofilm formation, and anthocyanin adsorption capacity. Community-level physiological profile analysis revealed that the microbial communities inside the barrels used the tested carbon sources in different manners. The following yeast species were identified: Millerozyma farinosa, Zygosaccharomyces bisporus, Wickerhamiella versatilis, Zygosaccharomyces bailii, Starmerella lactis-condensi, and Zygosaccharomyces rouxii. All the strains were able to produce GABA, and S. lactis-condensi, Z. bisporus and Z. rouxii were the highest producers (more than 600 mg/L). The Z. rouxii and Z. bailii strains showed the highest antioxidant activity. Only seven strains out of ten M. farinosa formed air-liquid interfacial biofilm. None of the M. farinosa strains adsorbed anthocyanins on their cell wall. The other strains adsorbed anthocyanins in a strain-dependent way, and the highest adsorption was observed for the W. versatilis strains. The yeasts isolated in this study could be used to increase the functional properties and the quality of fermented foods and beverages.

Antimicrobial Activity of Bacillus amyloliquefaciens BS4 against Gram-Negative Pathogenic Bacteria

Worldwide, bacterial resistance is one of the most severe public health problems. Currently, the failure of antibiotics to counteract superbugs highlights the need to search for new molecules with antimicrobial potential to combat them. The objective of this research was to evaluate the antimicrobial activity of Bacillus amyloliquefaciens BS4 against Gram-negative bacteria. Thirty yeasts and thirty-two Bacillus isolates were tested following the agar well-diffusion method. Four Bacillus sp. strains (BS3, BS4, BS17, and BS21) showed antagonistic activity against E. coli ATCC 25922 using bacterial culture (BC) and the cell-free supernatant (CFS), where the BS4 strain stood out, showing inhibitory values of 20.50 ± 0.70 mm and 19.67 ± 0.58 mm for BC and CFS, respectively. The Bacillus sp. BS4 strain can produce antioxidant, non-hemolytic, and antimicrobial metabolites that exhibit activity against several microorganisms such as Salmonella enterica, Klebsiella pneumoniae, Shigella flexneri, Enterobacter aerogenes, Proteus vulgaris, Yersinia enterocolitica, Serratia marcescens, Aeromonas sp., Pseudomonas aeruginosa, Candida albicans, and Candida tropicalis. According to the characterization of the supernatant, the metabolites could be proteinaceous. The production of these metabolites is influenced by carbon and nitrogen sources. The most suitable medium to produce antimicrobial metabolites was TSB broth. The one-factor-at-a-time method was used to standardize parameters such as pH, agitation, temperature, carbon source, nitrogen source, and salts, resulting in the best conditions of pH 7, 150 rpm, 28 °C, starch (2.5 g/L), tryptone (20 g/L), and magnesium sulfate (0.2 g/L), respectively. Moreover, the co-culture was an excellent strategy to improve antimicrobial activity, achieving maximum antimicrobial activity with an inhibition zone of 21.85 ± 1.03 mm. These findings position the Bacillus amyloliquefaciens BS4 strain as a promising candidate for producing bioactive molecules with potential applications in human health.

Purification and characterization of a Metschnikowia pulcherrima killer toxin with antagonistic activity against pathogenic microorganisms

Yeasts can produce toxins in protein or glycoprotein structures that can act as an inhibitor on some bacteria and yeast species. The effects of those toxins on the growth of pathogenic and food spoilage microorganisms are subject to various studies. Metschnikowia pulcherrima was determined to be a killer toxin-producing yeast that was tested against three selected microorganisms, namely Escherichia coli Type-I, Micrococcus luteus and Candida albicans. The killer toxin only showed inhibitory activity against M. luteus. Different pH (5-6-7-8), temperature (20-25-30-35 °C) and carbon source (glucose-glycerol-ethanol-acetate) combinations were applied to stimulate the growth and toxin production of the killer yeast. The greatest increase among the different combinations was obtained at 20 °C and pH 7 when glycerol was used as the main carbon source. It was then also tested against other pathogen indicators or pathogens under these conditions. The killer toxin was partially purified by ethanol precipitation and showed inhibitory activity against M. luteus (36 mm). According to the protein profile obtained by SDS-PAGE, the molecular weight of the inhibitor toxin was measured about 7.4 kDa. The molecular weight with amino acid sequence of the killer toxin was 10.3 kDa and determined by MALDI-TOF mass spectrometry.

The synthesis of soluble and volatile bioactive compounds by selected brewer's yeasts: Antagonistic effect against enteropathogenic bacteria and food spoiler - toxigenic Aspergillus sp

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Brewing fermentation residue possesses bacteriostatic and fungicidal activity.

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Crude brewing fermentation residue is an antimicrobial agent.

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Brewer’s yeasts secrete soluble and volatile bioactive compounds.

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Ethanol and 2,3-butanediol possess bacteriostatic and antifungal properties.

Contamination by Aspergillus sp. and the accumulation of its mycotoxins in food and beverages have a high impact on human health and food safety. This investigation inquires the ability of brewer’s yeasts discarded after fermentation (brewing fermentation residue, BFR) to synthesize bioactive compounds and to biocontrol Aspergillus sp. BFRs of Saccharomyces cerevisiae MBELGA62 and Pichia kudriavzevii MBELGA61 proved to have bacteriostatic properties and to be efficient in fungal growth reduction, decreasing the growth rate of Aspergillus flavus and Aspergillus parasiticus up to 37.8% and 42.5%, respectively. Fungal mycelium degradation along with absentia of conidia was detected near the yeast inoculum. Moreover, the yeasts synthesize volatile bioactive compounds that extend Aspergillus sp. lag phase above 100% and decrease fungal growth rates from 20% towards 44%, along with the complete inhibition of conidia synthesis. These results indicate the potential of this residue to be used in biocontrol applications in the food industry.

Potential probiotic yeast isolated from an Indonesian indigenous fermented fish (Ikan Budu)

Budu is a fermented food resulting from the activities of microorganisms like lactic acid bacteria and yeast. Budu, therefore, serves as a source of probiotics that can have beneficial effects on livestock and humans. Nonetheless, their selection has to be done with caution. The current study purposed to find out whether budu has desirable probiotic properties. This was done by determining its pH, bile acid tolerance, hydrophobicity, and inhibition of pathogens such as Staphylococcus aureus, Salmonella enteritidis, and Escherichia coli. An in vitro experiment was conducted using three Saccharomyces cerevisiae (coded as SC 11, SC 12, and SC 21) in the preparation of budu. The whole experiment was repeated four times. The budus were tested for their probiotic properties (low pH, bile salts, hydrophobicity, and inhibition of pathogenic bacteria). The results showed that the three Saccharomyces cerevisiae survived in gastric juice and bile acid, exhibited good hydrophobicity, and could inhibit pathogenic bacteria, both gram-positive and negative pathogens. They were able to survive at pH 2 for 3 h (40.70 to 55.1%), at pH 2 for 5 h (35.25 to 46.88%), in 0.3% bile acid incubated for 3 h (69.69 to 86.56%), in 0.3% bile acid incubated for 5 h (82.22 to 88.18%) and hydrophobicity ability of 97.0 to 98.1%. The inhibition activity against pathogenic bacteria, that is, Escherichia coli was 2.50 to 3.81 mm, Staphylococcus aureus was 1.66 to 3.71 mm, and Salmonella enteritidis was 1.20 to 2.64 mm.

A natural approach, the use of killer toxin produced by Metschnikowia pulcherrima in fresh ground beef patties for shelf life extention

A novel killer toxin produced by yeast Metschnikowia pulcherrima was purified and added into ready to cook meatballs to enhance their microbial safety and extension of their shelf life. The agent was added into ready to cook meatballs at two different concentrations (1%-K1 and 2%-K2). The results of those two groups were compared to the control group (K0) lacking the killer toxin. Physical, chemical and microbiological analyses were carried out in meat dough and all analyses were repeated at two day intervals during 10 day-storage at +4 °C. Addition of inhibitor compound in meat dough decreased the numbers of total aerobic mesophillic bacteria, yeast and molds and lactic acid bacteria. Staphylococci/Micrococci, coliform bacteria and total psychrotrophic bacterial counts of the samples were determined as well. Results showed that all indicators of microbial deterioration were found to be higher in K1 group than K2 group, revealing that there was an inverse correlation between the concentration of killer toxin and the number of microorganisms causing spoilage. In addition to 1 log decrease in the number of microorganisms in toxin added groups, the high TBARS values of the control group also showed the effectiveness of the toxin. Toxic effect analysis results showed that the killer toxin had no toxic effect on L929 mouse fibroblast cells after 24h exposure.

From Birth and Throughout Life: Fungal Microbiota in Nutrition and Metabolic Health

The human gastrointestinal tract is home to a vibrant, diverse ecosystem of prokaryotic and eukaryotic microorganisms. The gut fungi (mycobiota) have recently risen to prominence due to their ability to modulate host immunity. Colonization of the gut occurs through a combination of vertical transmission from the maternal mycobiota and environmental and dietary exposure. Data from human and animal studies demonstrate that nutrition strongly affects the mycobiota composition and that changes in the fungal communities can aggravate metabolic diseases. The mechanisms pertaining to the mycobiota's influence on host health, pathology, and resident gastrointestinal communities through intrakingdom, transkingdom, and immune cross talk are beginning to come into focus, setting the stage for a new chapter in microbiota-host interactions. Herein, we examine the inception, maturation, and dietary modulation of gastrointestinal and nutritional fungal communities and inspect their impact on metabolic diseases in humans.

Potential of Yeasts as Biocontrol Agents of the Phytopathogen Causing Cacao Witches' Broom Disease: Is Microbial Warfare a Solution?

Plant diseases caused by fungal pathogens are responsible for major crop losses worldwide, with a significant socio-economic impact on the life of millions of people who depend on agriculture-exclusive economy. This is the case of the Witches’ Broom Disease (WBD) affecting cacao plant and fruit in South and Central America. The severity and extent of this disease is prospected to impact the growing global chocolate market in a few decades. WBD is caused by the basidiomycete fungus Moniliophthora perniciosa. The methods used to contain the fungus mainly rely on chemical fungicides, such as copper-based compounds or azoles. Not only are these highly ineffective, but also their utilization is increasingly restricted by the cacao industry, in part because it promotes fungal resistance, in part related to consumers’ health concerns and environmental awareness. Therefore, the disease is being currently tentatively controlled through phytosanitary pruning, although the full removal of infected plant material is impossible and the fungus maintains persistent inoculum in the soil, or using an endophytic fungal parasite of Moniliophthora perniciosa which production is not sustainable. The growth of Moniliophthora perniciosa was reported as being antagonized in vitro by some yeasts, which suggests that they could be used as biological control agents, suppressing the fungus multiplication and containing its spread. Concurrently, some yeast-based products are used in the protection of fruits from postharvest fungal spoilage, and the extension of diverse food products shelf-life. These successful applications suggest that yeasts can be regarded a serious alternative also in the pre-harvest management of WBD and other fungal plant diseases. Yeasts’ GRAS (Generally Recognized as Safe) nature adds to their appropriateness for field application, not raising major ecological concerns as do the present more aggressive approaches. Importantly, mitigating WBD, in a sustainable manner, would predictably have a high socioeconomic impact, contributing to diminish poverty in the cacao-producing rural communities severely affected by the disease. This review discusses the importance/advantages and the challenges that such a strategy would have for WBD containment, and presents the available information on the molecular and cellular mechanisms underlying fungi antagonism by yeasts.

Yeast killer toxins: from ecological significance to application

Killer toxins are proteins that are often glycosylated and bind to specific receptors on the surface of their target microorganism, which is then killed through a target-specific mode of action. The killer phenotype is widespread among yeast and about 100 yeast killer species have been described to date. The spectrum of action of the killer toxins they produce targets spoilage and pathogenic microorganisms. Thus, they have potential as natural antimicrobials in food and for biological control of plant pathogens, as well as therapeutic agents against animal and human infections. In spite of this wide range of possible applications, their exploitation on the industrial level is still in its infancy. Here, we initially briefly report on the biodiversity of killer toxins and the ecological significance of their production. Their actual and possible applications in the agro-food industry are discussed, together with recent advances in their heterologous production and the manipulation for development of peptide-based therapeutic agents.

Successful Treatment of Catheter Related Blood Stream Infection By Millerozyma farinosa with Micafungin: A Case Report

Millerozyma farinosa (formerly Pichia farinosa) is halotolerant yeast mainly found in food and ubiquitous in the environment. It was a rare yeast pathogen, but it has recently emerged as a cause of fungemia in immunocompromised patients. Optimal therapy for invasive fungal infection by this pathogen remains unclear. We report a case of catheter related blood stream infection caused by M. farinosa in a 71-year-old patient who recovered successfully after removal of the central venous catheter and treatment with micafungin.

Edible Films and Coatings as Carriers of Living Microorganisms: A New Strategy Towards Biopreservation and Healthier Foods

Edible films and coatings have been extensively studied in recent years due to their unique properties and advantages over more traditional conservation techniques. Edible films and coatings improve shelf life and food quality, by providing a protective barrier against physical and mechanical damage, and by creating a controlled atmosphere and acting as a semipermeable barrier for gases, vapor, and water. Edible films and coatings are produced using naturally derived materials, such as polysaccharides, proteins, and lipids, or a mixture of these materials. These films and coatings also offer the possibility of incorporating different functional ingredients such as nutraceuticals, antioxidants, antimicrobials, flavoring, and coloring agents. Films and coatings are also able to incorporate living microorganisms. In the last decade, several works reported the incorporation of bacteria to confer probiotic or antimicrobial properties to these films and coatings. The incorporation of probiotic bacteria in films and coatings allows them to reach the consumers' gut in adequate amounts to confer health benefits to the host, thus creating an added value to the food product. Also, other microorganisms, either bacteria or yeast, can be incorporated into edible films in a biocontrol approach to extend the shelf life of food products. The incorporation of yeasts in films and coatings has been suggested primarily for the control of the postharvest disease. This work provides a comprehensive review of the use of edible films and coatings for the incorporation of living microorganisms, aiming at the biopreservation and probiotic ability of food products.

[Yeasts from the CTG clade (Candida clade): Biology, impact in human health, and biotechnological applications]

Among the subdivision of Saccharomycotina (ascomycetes budding yeasts), the CTG clade (formerly the Candida clade) includes species that display a particular genetic code. In these yeasts, the CTG codon is predominantly translated as a serine instead of a leucine residue. It is now well-known that some CTG clade species have a major impact on human and its activities. Some of them are recognized as opportunistic agents of fungal infections termed candidiasis. In addition, another series of species belonging to the CTG clade draws the attention of some research groups because they exhibit a strong potential in various areas of biotechnology such as biological control, bioremediation, but also in the production of valuable biocompounds (biofuel, vitamins, sweeteners, industrial enzymes). Here we provide an overview of recent advances concerning the biology, clinical relevance, and currently tested biotechnological applications of species of the CTG clade. Future directions for scientific research on these particular yeasts are also discussed.

Candida pyralidae killer toxin disrupts the cell wall of Brettanomyces bruxellensis in red grape juice

AIMS

The control of the wine spoilage yeast Brettanomyces bruxellensis using biological methods such as killer toxins (instead of the traditional chemical methods, e.g. SO₂ ) has been the focus of several studies within the last decade. Our previous research demonstrated that the killer toxins CpKT1 and CpKT2 isolated from the wine yeast Candida pyralidae were active and stable under winemaking conditions. In this study, we report the possible mode of action of CpKT1 on B. bruxellensis cells in red grape juice.

METHODS AND RESULTS

Brettanomyces bruxellensis cells were exposed to CpKT1 either directly or through co-inoculation with C. pyralidae. This exposure yielded a temporary or permanent decline of the spoilage yeast population depending on the initial cell concentration. Scanning electron microscopy revealed cell surface abrasion while propidium iodide viability staining showed that CpKT1 caused plasma membrane damage on B. bruxellensis cells. Our data show that the exposure to CpKT1 resulted in increased levels of β-glucan, suggesting a compensatory response of the sensitive cells.

CONCLUSIONS

The toxin CpKT1 causes cell membrane and cell wall damage in B. bruxellensis.

SIGNIFICANCE AND IMPACT OF THE STUDY

Candida pyralidae shows potential to be used as a biocontrol agent against B. bruxellensis in grape juice/wine.

Identification and Partial Characterization of Antilisterial Compounds Produced by Dairy Yeasts

Food-grade yeasts make significant contributions to flavor development in fermented foods. Some yeast species also inhibit undesirable bacteria, yeasts and molds, apparently by producing antimicrobial compounds called mycocins. The aim of this study was to evaluate the ability of wild yeasts, isolated from raw milk and cheese in the Quebec province area, to produce antilisterial compounds. Based on an agar-membrane screening test, 22 of 95 isolates, namely one Candida catenulata, one Candida parapsilosis, five Candida tropicalis, four Debaryomyces hansenii, one Geotrichum candidum, nine Pichia fermentans and one Pichia anomala, exhibited a significant inhibitory effect against Listeria ivanovii HPB28. Four in particular, namely C. tropicalis LMA-693, D. hansenii LMA-916, P. fermentans LMA-256 and P. anomala LMA-827, produced substances extractable from culture supernatant and capable of decreasing 18-h growth of L. ivanovii by, respectively, 97, 92, 84 and 78 %. Heating the extracted material (100 °C for 10 min) decreased these values to 72, 62, 58 and 31 %, respectively, while treatment with trypsin or pronase E decreased them to as little as 27 %. The extracts reduced the numbers of viable Listeria monocytogenes by as much as four log cycles within an hour. Transmission electron microscopy revealed a high proportion of lysis among the cells, apparently due to pore formation. This study clearly shows the potential of these four yeast isolates for use as bio-preservatives in a variety of dairy products.

Bioprotective Role of Yeasts

The yeasts constitute a large group of microorganisms characterized by the ability to grow and survive in different and stressful conditions and then to colonize a wide range of environmental and human ecosystems. The competitive traits against other microorganisms have attracted increasing attention from scientists, who proposed their successful application as bioprotective agents in the agricultural, food and medical sectors. These antagonistic activities rely on the competition for nutrients, production and tolerance of high concentrations of ethanol, as well as the synthesis of a large class of antimicrobial compounds, known as killer toxins, which showed clearly a large spectrum of activity against food spoilage microorganisms, but also against plant, animal and human pathogens. This review describes the antimicrobial mechanisms involved in the antagonistic activity, their applications in the processed and unprocessed food sectors, as well as the future perspectives in the development of new bio-drugs, which may overcome the limitations connected to conventional antimicrobial and drug resistance.

Towards defining the substrate of orphan P5A-ATPases

BACKGROUND

P-type ATPases are ubiquitous ion and lipid pumps found in cellular membranes. P5A-ATPases constitute a poorly characterized subfamily of P-type ATPases present in all eukaryotic organisms but for which a transported substrate remains to be identified.

SCOPE OF REVIEW

This review aims to discuss the available evidence which could lead to identification of possible substrates of P5A-ATPases.

MAJOR CONCLUSIONS

The complex phenotypes resulting from the loss of P5A-ATPases in model organisms can be explained by a role of the P5A-ATPase in the endoplasmic reticulum (ER), where loss of function leads to broad and unspecific phenotypes related to the impairment of basic ER functions such as protein folding and processing. Genetic interactions in Saccharomyces cerevisiae point to a role of the endogenous P5A-ATPase Spf1p in separation of charges in the ER, in sterol metabolism, and in insertion of tail-anchored proteins in the ER membrane. A role for P5A-ATPases in vesicle formation would explain why sterol transport and distribution are affected in knock out cells, which in turn has a negative impact on the spontaneous insertion of tail-anchored proteins. It would also explain why secretory proteins destined for the Golgi and the cell wall have difficulties in reaching their final destination. Cations and phospholipids could both be transported substrates of P5A-ATPases and as each carry charges, transport of either might explain why a charge difference arises across the ER membrane.

GENERAL SIGNIFICANCE

Identification of the substrate of P5A-ATPases would throw light on an important general process in the ER that is still not fully understood. This article is part of a Special Issue entitled Structural biochemistry and biophysics of membrane proteins.

The biology of habitat dominance; can microbes behave as weeds?

Competition between microbial species is a product of, yet can lead to a reduction in, the microbial diversity of specific habitats. Microbial habitats can resemble ecological battlefields where microbial cells struggle to dominate and/or annihilate each other and we explore the hypothesis that (like plant weeds) some microbes are genetically hard-wired to behave in a vigorous and ecologically aggressive manner. These 'microbial weeds' are able to dominate the communities that develop in fertile but uncolonized--or at least partially vacant--habitats via traits enabling them to out-grow competitors; robust tolerances to habitat-relevant stress parameters and highly efficient energy-generation systems; avoidance of or resistance to viral infection, predation and grazers; potent antimicrobial systems; and exceptional abilities to sequester and store resources. In addition, those associated with nutritionally complex habitats are extraordinarily versatile in their utilization of diverse substrates. Weed species typically deploy multiple types of antimicrobial including toxins; volatile organic compounds that act as either hydrophobic or highly chaotropic stressors; biosurfactants; organic acids; and moderately chaotropic solutes that are produced in bulk quantities (e.g. acetone, ethanol). Whereas ability to dominate communities is habitat-specific we suggest that some microbial species are archetypal weeds including generalists such as: Pichia anomala, Acinetobacter spp. and Pseudomonas putida; specialists such as Dunaliella salina, Saccharomyces cerevisiae, Lactobacillus spp. and other lactic acid bacteria; freshwater autotrophs Gonyostomum semen and Microcystis aeruginosa; obligate anaerobes such as Clostridium acetobutylicum; facultative pathogens such as Rhodotorula mucilaginosa, Pantoea ananatis and Pseudomonas aeruginosa; and other extremotolerant and extremophilic microbes such as Aspergillus spp., Salinibacter ruber and Haloquadratum walsbyi. Some microbes, such as Escherichia coli, Mycobacterium smegmatis and Pseudoxylaria spp., exhibit characteristics of both weed and non-weed species. We propose that the concept of nonweeds represents a 'dustbin' group that includes species such as Synodropsis spp., Polypaecilum pisce, Metschnikowia orientalis, Salmonella spp., and Caulobacter crescentus. We show that microbial weeds are conceptually distinct from plant weeds, microbial copiotrophs, r-strategists, and other ecophysiological groups of microorganism. Microbial weed species are unlikely to emerge from stationary-phase or other types of closed communities; it is open habitats that select for weed phenotypes. Specific characteristics that are common to diverse types of open habitat are identified, and implications of weed biology and open-habitat ecology are discussed in the context of further studies needed in the fields of environmental and applied microbiology.

Antimicrobial and probiotic properties of yeasts: from fundamental to novel applications

The yeasts constitute a large and heterogeneous group of microorganisms that are currently attracting increased attention from scientists and industry. Numerous and diverse biological activities make them promising candidates for a wide range of applications not limited to the food sector. In addition to their major contribution to flavor development in fermented foods, their antagonistic activities toward undesirable bacteria, and fungi are now widely known. These activities are associated with their competitiveness for nutrients, acidification of their growth medium, their tolerance of high concentrations of ethanol, and release of antimicrobial compounds such as antifungal killer toxins or "mycocins" and antibacterial compounds. While the design of foods containing probiotics (microorganisms that confer health benefits) has focused primarily on Lactobacillus and Bifidobacterium, the yeast Saccharomyces cerevisiae var. boulardii has long been known effective for treating gastroenteritis. In this review, the antimicrobial activities of yeasts are examined. Mechanisms underlying this antagonistic activity as well as recent applications of these biologically active yeasts in both the medical and veterinary sectors are described.

Ca2+ induces spontaneous dephosphorylation of a novel P5A-type ATPase

P5 ATPases constitute the least studied group of P-type ATPases, an essential family of ion pumps in all kingdoms of life. Although P5 ATPases are present in every eukaryotic genome analyzed so far, they have remained orphan pumps, and their biochemical function is obscure. We show that a P5A ATPase from barley, HvP5A1, locates to the endoplasmic reticulum and is able to rescue knock-out mutants of P5A genes in both Arabidopsis thaliana and Saccharomyces cerevisiae. HvP5A1 spontaneously forms a phosphorylated reaction cycle intermediate at the catalytic residue Asp-488, whereas, among all plant nutrients tested, only Ca(2+) triggers dephosphorylation. Remarkably, Ca(2+)-induced dephosphorylation occurs at high apparent [Ca(2+)] (K(i) = 0.25 mM) and is independent of the phosphatase motif of the pump and the putative binding site for transported ligands located in M4. Taken together, our results rule out that Ca(2+) is a transported substrate but indicate the presence of a cytosolic low affinity Ca(2+)-binding site, which is conserved among P-type pumps and could be involved in pump regulation. Our work constitutes the first characterization of a P5 ATPase phosphoenzyme and points to Ca(2+) as a modifier of its function.

Structural divergence between the two subgroups of P5 ATPases

Evolution of P5 type ATPases marks the origin of eukaryotes but still they remain the least characterized pumps in the superfamily of P-type ATPases. Phylogenetic analysis of available sequences suggests that P5 ATPases should be divided into at least two subgroups, P5A and P5B. P5A ATPases have been identified in the endoplasmic reticulum and seem to have basic functions in protein maturation and secretion. P5B ATPases localize to vacuolar/lysosomal or apical membranes and in animals play a role in hereditary neuronal diseases. Here we have used a bioinformatical approach to identify differences in the primary sequences between the two subgroups. P5A and P5B ATPases appear have a very different membrane topology from other P-type ATPases with two and one, respectively, additional transmembrane segments inserted in the N-terminal end. Based on conservation of residues in the transmembrane region, the two P5 subgroups most likely have different substrate specificities although these cannot be predicted from their sequences. Furthermore, sequence differences between P5A and P5B ATPases are identified in the catalytic domains that could influence key kinetic properties differentially. Together these findings indicate that P5A and P5B ATPases are structurally and functionally different.

Pichia farinosa bloodstream infection in a lymphoma patient

We describe a case of Pichia farinosa bloodstream infection in a lymphoma patient. Phenotypic methods failed to identify the isolate, which was identified by sequence-based methods. This case highlights the importance of implementing molecular methods for the identification of rare fungal pathogens.

The role of the histidine-35 residue in the cytocidal action of HM-1 killer toxin

Diethylpyrocarbonate modification and site-directed mutagenesis studies of histidine-35 in HM-1 killer toxin (HM-1) have shown that a specific feature, the imidazole side chain of histidine-35, is essential for the expression of the killing activity. In subcellular localization experiments, wild-type HM-1 was in the membrane fraction of Saccharomyces cerevisiae BJ1824, but not the HM-1 analogue in which histidine-35 was replaced by alanine (H35A HM-1). Neither wild-type nor H35A HM-1 was detected in cellular fractions of HM-1-resistant yeast S. cerevisiae BJ1824 rhk1Δ : : URA3 and HM-1-insensitive yeast Candida albicans even after 1 h incubation. H35A HM-1 inhibited the activity of partially purified 1,3-β-glucan synthase from S. cerevisiae A451, and its extent was almost the same as wild-type HM-1. Co-immunoprecipitation experiments showed that wild-type and H35A HM-1 directly interact with the 1,3-β-glucan synthase complex. These results strongly suggest that histidine-35 has an important role in the cytocidal action of HM-1 that participates in the binding process to the HM-1 receptor protein on the cell membrane, but it is not essential for the interaction with, and inhibition of, 1,3-β-glucan synthase.

The endoplasmic reticulum cation P-type ATPase Cta4p is required for control of cell shape and microtubule dynamics

Here we describe the phenotypic characterization of the cta4+ gene, encoding a novel member of the P4 family of P-type ATPases of fission yeast. The cta4Delta mutant is temperature sensitive and cold sensitive lethal and displays several morphological defects in cell polarity and cytokinesis. Microtubules are generally destabilized in cells lacking Cta4p. The microtubule length is decreased, and the number of microtubules per cell is increased. This is concomitant with an increase in the number of microtubule catastrophe events in the midzone of the cell. These defects are likely due to a general imbalance in cation homeostasis. Immunofluorescence microscopy and membrane fractionation experiments revealed that green fluorescent protein-tagged Cta4 localizes to the ER. Fluorescence resonance energy transfer experiments in living cells using the yellow cameleon indicator for Ca2+ indicated that Cta4p regulates the cellular Ca2+ concentration. Thus, our results reveal a link between cation homeostasis and the control of cell shape, microtubule dynamics, and cytokinesis, and appoint Ca2+ as a key ion in controlling these processes.