Pichia Kluyveri Research Articles

Modeling mixed fermentation of gowé using selected Lactobacillus plantarum and Pichia kluyveri strains

This paper describes a mixed fermentation model made by assembling block hosting models for the growth of lactic acid bacteria (Lactobacillus plantarum) and a yeast strain (Pichia kluyveri), metabolic production and the physical-chemical changes which occur during the fermentation of gowé. The growth model for P. kluyveri was developed on a synthetic medium following the gamma concept taking into account the effect of pH, temperature, concentrations in glucose, lactic acid and ethanol. Additional parameters for the previously defined L. plantarum growth model were also determined (glucose and ethanol concentrations). The model was validated in three different gowé processing conditions. Even if the model underestimates LAB growth, it explains what occurs in the product and enables in silico extrapolation to various fermentation conditions. The predicted hydrolysis rates of native and gelatinised starches showed that increasing malt content is not an efficient way to increase the sweetness of gowé in contrast to increasing the level of pre-cooking. The builing-block model developed in this study could be applied to many other fermented foods and particularly to non-alcoholic but acid and sweet cereal based beverages.

Modulating Fermentative, Varietal and Aging Aromas of Wine Using non-Saccharomyces Yeasts in a Sequential Inoculation Approach.

The goal of this study is to assess to what extent non-Saccharomyces yeasts can introduce aromatic changes of industrial interest in fermentative, varietal and aged aromas of wine. Aroma precursors from Riesling and Garnacha grapes were extracted and used in two independent sequential experiments. Synthetic musts were inoculated, either with Saccharomyces cerevisiae (Sc) or with Pichia kluyveri (Pk), Torulaspora delbrueckii (Td) or Lachancea thermotolerans (Lt), followed by Sc. The fermented samples were subjected to anoxic aging at 50 °C for 0, 1, 2 or 5 weeks before an aroma analysis. The fermentative aroma profiles were consistently changed by non-Saccharomyces: all strains induced smaller levels of isoamyl alcohol; Pk produced huge levels of aromatic acetates and can induce high levels of fatty acids (FA) and their ethyl esters (EE); Td produced large levels of branched acids and of their EE after aging, and induced smaller levels of FA and their EE; Lt produced reduced levels of FA and their EE. The varietal aroma was also deeply affected: TDN (1,1,6-trimethyl-1,2- dihydronaphthalene) levels in aged wines were reduced by Pk and enhanced by Lt in Garnacha; the levels of vinylphenols can be much reduced, particularly by Lt and Pk. TD and Lt can increase linalool and geraniol in young, but not in aged wines.

Gut yeasts do not improve desiccation survival in Drosophila melanogaster

A healthy gut microbiota generally improves the performance of its insect host. Although the effects can be specific to the species composition of the microbial community, the role of gut microbiota in determining water balance has not been well explored. We used axenic and gnotobiotic (reared with a known microbiota) Drosophila melanogaster to test three hypotheses about the effects of gut yeasts on the water balance of adult flies: 1) that gut yeasts would improve desiccation survival in adult flies; 2) that larval yeasts would improve adult desiccation survival; 3) that the effects would be species-specific, such that yeasts closely associated with D. melanogaster in nature are more likely to be beneficial than those rarely found in association with D. melanogaster. We used Saccharomyces cerevisiae (often used in Drosophila cultures, but rarely associated with D. melanogaster in nature), Lachancea kluyveri (associated with some species of Drosophila, but not D. melanogaster), and Pichia kluyveri (associated with D. melanogaster in nature). Adult inoculation with yeasts had no effect on survival of desiccating conditions. Inoculation with P. kluyveri as larvae did not change desiccation survival in adults; however, rearing with L. kluyveri or S. cerevisiae reduced adult desiccation survival. We conclude that adult inoculation with gut yeasts has no impact on desiccation survival, but that rearing with yeasts can have either no or detrimental effect. The effects appear to be species-specific: P. kluyveri did not have a negative impact on desiccation tolerance, suggesting some level of co-adaptation with D. melanogaster. We note that S. cerevisiae may not be an appropriate species for studying the effects of gut yeasts on D. melanogaster.

Grape Pomace Extracts as Fermentation Medium for the Production of Potential Biopreservation Compounds.

Microbial spoilage causes food losses in the food industry and as such, the use of synthetic chemical preservatives is still required. The current study proposes the use of agro-waste, i.e., grape pomace extracts (GPE), as production medium for biopreservation compounds. Production kinetics, subsequent to optimization using response surface methodology (RSM) for biopreservation compounds production was studied for three yeasts using GPE broth as a fermentation medium. The results showed that the highest volumetric zone of inhibition (VZI) was 1.24 L contaminated solidified media (CSM) per mL biopreservation compounds used (BCU) when Candida pyralidae Y1117 was inoculated in a pH 3-diluted GPE broth (150 g L−1) incubated at 25 °C for 24 h. Similar conditions were applied for Pichia kluyveri Y1125 and P. kluyveri Y1164, albeit under slightly elongated fermentation periods (up to 28 h), prior to the attainment of a maximum VZI of only 0.72 and 0.76 L CSM mL−1 ACU, respectively. The potential biopreservation compounds produced were identified to be isoamyl acetate, isoamyl alcohol, 2-phenyl ethylacetate and 2-phenyl ethanol.

The utilisation of nitrogenous compounds by commercial non-Saccharomyces yeasts associated with wine

Commercial wine fermentation is commonly conducted by inoculated strains of Saccharomyces cerevisiae. However, other non-Saccharomyces yeast species have recently become popular co-inoculants. Co-inoculated yeast species compete with each other for nutrients, and such competition may impact fermentation kinetics and aroma production. Understanding the specific nutrient requirements of non-Saccharomyces strains therefore is essential to better characterize the competitive potential of each strain, and to support rational decision making for nutrient supplementation during wine making. This study investigated the nitrogen source preference of commercial non-Saccharomyces yeasts by conducting pure culture and sequential culture fermentations in synthetic grape musts with adjusted nitrogen contents. Amino acid and ammonium uptake varied between yeast species. Lachancea thermotolerans and Torulaspora delbrueckii assimilated more nitrogen at a faster rate than Pichia kluyveri and Metschnikowia pulcherrima. Significant variation in amino acid preference between species was observed. Sequential fermentations confirmed the more competitive behaviour of L. thermotolerans and T. delbrueckii, with consequences for fermentation kinetics and aroma production. Furthermore, the data suggest that declining populations of non-Saccharomyces yeasts release nitrogen and supports the activity of S. cerevisiae. The data provide the most detailed assessment of nitrogen utilisation by the investigated yeast strains in a wine environment.

Characteristic fruit wine production via reciprocal selection of juice and non-Saccharomyces species

This study examines the effect of juices and non-Saccharomyces yeasts on physicochemical properties and sensory quality for fruit wines. Here, fruit wines produced from six kinds of fruit juices and eight non-Saccharomyces yeasts were evaluated, and the results show significant phenotypic diversity within these yeasts for wine fermentation on a range of substrates. Substantial variations in indicators such as total acid, sugar content and organic acid content were observed, which were caused by selection of both yeasts and juice types. These differences in characteristics had an impact on consumer preference. Considering overall acceptance by the panelists, correspondence analysis showed that Pichia kluyveri X31-10 (Pk31) was the most suitable strain for apple juice fermentation, and Fuji apple juice was the best substrate for this fermentation. A partial least-squares regression model of aroma characteristics against aroma components revealed that acetate esters were the primary contributors to tropical fruit aroma notes of ciders from Pk31. Additionally, 1-butanol, 3-methyl-, acetate; acetic acid, hexyl ester; and acetic acid, pentyl ester have been implicated as characteristic volatiles associated with Pk31.

Community structures and genomic features of undesirable white colony-forming yeasts on fermented vegetables.

White colony-forming yeasts (WCFYs) often appear in fermented foods, depending on the storage method. Despite the ongoing research on fermented foods, the community and genome features of WCFYs have not been well studied. In this study, the community structures of WCFYs on fermented vegetables (kimchi) prepared with various raw materials were investigated using deep sequencing. Only eight operational taxonomic units (OTUs) were detected, indicating that the community structure of WCFYs on kimchi is very simple. The five most abundant OTUs represented Pichia kluyveri, Yarrowia lipolytica, Candida sake, Hanseniaspora uvarum, and Kazachstania servazzii. Using a culture-dependent method, 41 strains representing the five major OTUs were isolated from the surface of the food samples. Whole genomes of the five major yeast strains were sequenced and annotated. The total genome length for the strains ranged from 8.97 Mbp to 21.32 Mbp. This is the first study to report genome sequences of the two yeasts Pichia kluyveri and Candida sake. Genome analysis indicated that each yeast strain had core metabolic pathways such as oxidative phosphorylation; purine metabolism; glycolysis/gluconeogenesis; aminoacyl-tRNA biosynthesis; citrate cycle; but strain specific pathways were also found. In addition, no toxin or antimicrobial resistance genes were identified. Our study provides genome information for five WCFY strains that may highlight their potential beneficial or harmful metabolic effects in fermented vegetables.

Development of air-blast dried non-Saccharomyces yeast starter for improving quality of Korean persimmon wine and apple cider

A total of 512 yeasts, including 422 non-Saccharomyces yeasts, were isolated from various fruits including apple, aronia, Muscat Bailey A grapes, and persimmon. These were used to prepare persimmon wine and apple cider starters that produced high levels of aromatic compounds, which contribute to high-quality fermented products. Environmental tolerance testing with 20% glucose and 8% EtOH, alongside a sniffing test, led to the selection of Wickerhamomyces anomalus (Synonym Pichia anomala) SJ20, Meyerozyma caribbica (Synonym Pichia caribbica) YP1, Pichia kluyveri CD34, Hanseniaspora uvarum SJ69 (for persimmon wine), W. anomalus CS7-16 (for apple cider), and Starmerella bacillaris (Synonym Candida zemplinina) CD80 (for both wines) as wine starters. These strains had high environmental stress tolerance and the highest sniffing test scores. Persimmon wine and apple cider were fermented using these strains in single- or mixed-culture with S. cerevisiae W-3 to determine the improved effect on wine aroma. In accordance with the results of volatile ester compounds and sensory evaluation, W. anomalus SJ20, H. uvarum SJ69, and W. anomalus CS7-16 had an excellent potential as persimmon wine and apple cider starters. Moreover, other strains also showed a good potential for a distinctive persimmon wine and apple cider because of the different compositions of the various volatile ester compounds. Six types of sugars (fructose, glucose, maltose, sucrose, raffinose, sucrose, and trehalose), four types of rehydration solutions (distilled water, 1× phosphate buffered saline, 0.85% NaCl, and 1% peptone water), and two types of antioxidants (l-ascorbic acid and glutathione) were examined to improve the survival rate of air-blast dried non-Saccharomyces yeast cells. Optimal sugar and rehydration conditions for each strain were validated, and scanning electron microscopy showed that each cell was surrounded by protectants, including sugar, skim milk, and lactomil. Storability assessment of air-blast dried yeast cells maintained at 4 °C for two months indicated that at least one condition in each strain had a higher survival rate than the control, regardless of the concentration or type of antioxidant treatment, except for M. caribbica YP1. These results suggest that antioxidant treatment contributes to maintaining the viability of air-blast dried cells in hostile environments.

Green production of bio-ethanol from cellulosic fiber waste and its separation using polyacrylonitrile-co-poly methyl acrylate membrane

The world is currently suffering substantially from the over-use of fossil fuels and worsening global climate change. The recycling and conversion of various types of biomass wastes for production of bio-ethanol have recently received increasing interest around the world to overcome the upcoming fuel shortage. In this work, the cellulosic fibers from textile industry wastes were used as biomass resource for liberation of glucose units. The cellulosic fibers were treated by some acids or alkali reagents followed by application of ultrasonic waves or autoclaving or microwave radiation as green technologies for improving hydrolysis rate. The cellulase enzyme from Trichoderma reesei was later applied to increase the concentration of glucose yield to reach 1133.33 mg/dl. Glucose units were then fermented by yeast isolate that was identified by amplification and sequencing of 18S rRNA as Pichia kluyveri (accession number MF184994). The parameters of pH, temperature, inoculum size, and aerobic/anaerobic conditions were optimized revealing that cultivation of 10% of the yeast isolate at pH 5 and 25 °C under anaerobic conditions are the ideal parameters for higher bio-ethanol production rates (33.9%). The produced bio-ethanol compared with standard 25% ethanol was separated by using amicon cell ultra-filtration that contains poly acrylonitrile co methyl acrylate membrane at different nitrogen pressures. The membrane was characterized by SEM, FTIR, Raman spectroscopy, TGA, IEC, and tensile strength measurement. The hydrophilicity/hydrophobicity of the prepared membrane was investigated using contact angle and water/ethanol uptake. Finally, the prepared polymeric membrane integrated amicon cell succeeded to increase the prepared ethanol concentration from 194.25 to 478.74 mg/ml which approximately elevated from 25 to 61.6%. On the other hand, the bio-ethanol concentration was increased from 256.41 to 540.82 mg/ml which approximately elevated from 33.9 to 69.6%. The obtaining bioethanol concentration is considered cost efficient, where the combined fermentation and separation processes succeeded to convert one ton of cellulosic fiber wastes into 105 l of bioethanol with approximate estimation cost of 103.9$ per liter through lab scale study.

Yeast distribution in Grignolino grapes growing in a new vineyard in Piedmont and the technological characterization of indigenous Saccharomyces spp. strains

The aim of this study was to characterize the yeast consortium isolated from Grignolino grapes in a newly planted vineyard in Piedmont (Italy) via analysis of the intra-vineyard yeast distribution of grape samples from single rows. A two-phase approach allowed the identification of culturable yeasts present on grape skins and, through an enriching procedure via grape fermentation, the isolation of low frequency non-Saccharomyces and Saccharomyces spp. fermentative species, including S. paradoxus, which is highly unusual during grape fermentation, along with the intra-specific characterization of S. cerevisiae isolates. Culture-based molecular techniques revealed a grape yeast microbiota formed by (in order of abundance) Hanseniaspora uvarum, the yeast-like fungus Aerobasidium pullulans, Candida zemplinina, Pichia kluyveri, Candida californica, Curvibasidium cygneicollum, Meyerozima caribbica, Rhodotorula babjevae, Metschnikowia pulcherrima and Cryptococcus flavescens. Technological properties of isolated Saccharomyces spp. strains were analysed, identifying strains, including S. paradoxus, potentially suitable as an ecotypical starter for territorial wines.

Evaluation of non-Saccharomyces yeasts in the fermentation of wine, beer and cider for the development of new beverages

Non‐Saccharomyces yeasts were evaluated for their fermentation properties and the production of pleasant fruity aromas in three industrial media (beer, wine and cider). A total of 99 yeasts were screened for aroma production using a simple olfactory plate assay. Of these, 21 yeasts were further evaluated for their aroma profile and fermentation capacity using wort, grape and apple juice. The most promising yeasts were Galactomyces geotrichum (three strains), Kazachstania zonata, Kluyveromyces lactis, Lindnera meyerae, Pichia kluyveri, Starmera caribae, Yarrowia lipolytica and Saccharomycodes ludwigii. This study confirms the potential of non‐conventional yeasts to produce pleasant aroma compounds under relevant fermentation conditions. In general, differences in the medium composition had less impact on the overall aroma profile than the choice of yeast. This study is the first to simultaneously evaluate multiple non‐conventional yeasts in three different industrial media. The results reported here are a good starting point for the development of novel fermented beverages.

Maximum residue limit of fungicides inhibits the viability and growth of desirable non-Saccharomyceswine yeasts

Background and Aims Fungicides used against the mould Botrytis cinerea can also non-specifically affect indigenous yeasts important for the development of complex wine aroma. Our aim was to determine the minimal inhibitory concentration of the fungicides iprodione, pyrimethanil and fludioxonil plus cyprodinil for 109 yeasts of the grape berry microbiota. Methods and Results We measured the respiration activity of yeasts, changes in growth kinetics and adenosine triphosphate production. Fungicide tolerance may be a conserved feature within the yeast's genera, however, some heterogeneity between isolates remains. The viability and growth of 15 beneficial isolates were inhibited by fungicides at a residue concentration below the maximum permitted residue limits. These isolates belonged to the yeast species: Metschnikowia pulcherrima, Pichia kluyveri, Hanseniaspora uvarum and Bulleromyces albus. Furthermore, isolates of typical spoilage yeasts, such as Dekkera bruxellensis, Meyerozyma guilliermondii and Pichia membranifaciens, were found to be tolerant of a concentration of fungicides greater than that recommended for application by the suppliers. Conclusions Fungicide residues hindered the viability of desirable isolates and promoted the growth of several spoilage isolates and thus may have a negative impact on wine aroma. Significance of the Study For spontaneous fermentations the application of fungicides in the vineyard could add to the seasonal fluctuations of aroma and to the development of off-flavours.

Evaluation of five commercial non-Saccharomyces yeasts in fermentation of soy (tofu) whey into an alcoholic beverage

Soy (tofu) whey is a nutritious liquid substrate that is often discarded by tofu manufacturers. Recent research has shown that tofu whey can be converted into a soy alcoholic beverage using Saccharomyces yeasts. In this study, five commercially available non-Saccharomyces yeasts (Torulaspora delbrueckii; Lachancea thermotolerans; Metschnikowia pulcherrima; Pichia kluyveri and Williopsis saturnus) were evaluated in tofu whey fermentation and each of the yeasts showed different growth kinetics and fermentation performance. T. delbrueckii and L. thermotolerans consumed the supplemented sucrose and produced 6–7% (v/v) ethanol, while M. pulcherrima, P. kluyveri and W. saturnus only utilized the endogenous fructose and glucose, producing trace levels of ethanol. Besides, different yeasts showed different β-glucosidase activities with 22–97% reduction in isoflavone glucosides; T. delbrueckii, L. thermotolerans and W. saturnus also decreased the level of GABA in tofu whey. Endogenous volatile compounds (mainly short-chain aldehydes) in tofu whey were reduced to trace levels, but different volatile compounds were produced by different yeasts at varying levels that can contribute to the different aroma profiles of the beverages. Therefore, selection of appropriate non-Saccharomyces yeasts can serve as a new strategy to valorize tofu whey and alter the aroma profile of the beverage.

Characterization of antagonistic yeasts for biocontrol applications on apples or in soil by quantitative analyses of synthetic yeast communities.

Antagonistic yeasts suppress plant pathogenic fungi by various mechanisms, but their biocontrol efficacy also depends on the ability to compete and persist in the environment. The goal of the work presented here was to quantify the composition of synthetic yeast communities in order to determine the competitiveness of different species and identify promising candidates for plant protection. For this purpose, colony counting of distinct species and matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS; MALDI biotyping) were used to distinguish different yeast species and to quantify the composition of a synthetic community of six yeasts (Aureobasidium pullulans, Candida subhashii, Cyberlindnera sargentensis, Hanseniaspora sp., Metschnikowia pulcherrima and Pichia kluyveri) over time, on apples and in soil, and in different growth media. These studies revealed important characteristics that predispose the different species for particular applications. For example, the competitiveness and antagonistic activity of C. subhashii was strongly increased in the presence of N‐acetylglucosamin as the sole carbon source, M. pulcherrima and A. pullulans were the strongest competitors on apple, and C. sargentensis competed the best in soil microcosms. Based on these laboratory studies, M. pulcherrima and A. pullulans are promising candidates for biocontrol applications against fungal phyllosphere diseases, while C. sargentensis may hold potential for use against soilborne fungal pathogens. These results document the potential of MALDI‐TOF MS for the quantitative analysis of synthetic yeast communities and highlight the value of studying microorganisms with relevant functions in moderately complex, synthetic communities and natural substrates rather than as individual isolates.

New oenological practice to promote non-Saccharomyces species of interest: saturating grape juice with carbon dioxide

Non-Saccharomyces yeast species, naturally found in grape must, may impact wine quality positively or negatively. In this study, a mixture of five non-Saccharomyces species (Torulaspora delbrueckii, Metschnikowia spp., Starmerella bacillaris (formerly called Candida zemplinina), Hanseniaspora uvarum, Pichia kluyveri), mimicking the composition of the natural non-Saccharomyces community found in grape must, was used for alcoholic fermentation. The impact of CO2 saturation of the grape juice was studied first on this mixture alone, and then in the presence of Saccharomyces cerevisiae. Two isogenic strains of this species were used: the first with a short and the second a long fermentation lag phase. This study demonstrated that saturating grape juice with CO2 had interesting potential as an oenological technique, inhibiting undesirable species (S. bacillaris and H. uvarum) and stimulating non-Saccharomyces of interest (T. delbrueckii and P. kluyveri). This stimulating effect was particularly marked when CO2 saturation was associated with the presence of S. cerevisiae with long fermentation lag phase. The direct consequence of this association was an enhancement of 3-SH levels in the resulting wine.

Chemical signaling and insect attraction is a conserved trait in yeasts.

Yeast volatiles attract insects, which apparently is of mutual benefit, for both yeasts and insects. However, it is unknown whether biosynthesis of metabolites that attract insects is a basic and general trait, or if it is specific for yeasts that live in close association with insects. Our goal was to study chemical insect attractants produced by yeasts that span more than 250 million years of evolutionary history and vastly differ in their metabolism and lifestyle. We bioassayed attraction of the vinegar fly Drosophila melanogaster to odors of phylogenetically and ecologically distinct yeasts grown under controlled conditions. Baker's yeast Saccharomyces cerevisiae, the insect‐associated species Candida californica, Pichia kluyveri and Metschnikowia andauensis, wine yeast Dekkera bruxellensis, milk yeast Kluyveromyces lactis, the vertebrate pathogens Candida albicans and Candida glabrata, and oleophilic Yarrowia lipolytica were screened for fly attraction in a wind tunnel. Yeast headspace was chemically analyzed, and co‐occurrence of insect attractants in yeasts and flowering plants was investigated through a database search. In yeasts with known genomes, we investigated the occurrence of genes involved in the synthesis of key aroma compounds. Flies were attracted to all nine yeasts studied. The behavioral response to baker's yeast was independent of its growth stage. In addition to Drosophila, we tested the basal hexapod Folsomia candida (Collembola) in a Y‐tube assay to the most ancient yeast, Y. lipolytica, which proved that early yeast signals also function on clades older than neopteran insects. Behavioral and chemical data and a search for selected genes of volatile metabolites underline that biosynthesis of chemical signals is found throughout the yeast clade and has been conserved during the evolution of yeast lifestyles. Literature and database reviews corroborate that yeast signals mediate mutualistic interactions between insects and yeasts. Moreover, volatiles emitted by yeasts are commonly found also in flowers and attract many insect species. The collective evidence suggests that the release of volatile signals by yeasts is a widespread and phylogenetically ancient trait, and that insect–yeast communication evolved prior to the emergence of flowering plants. Co‐occurrence of the same attractant signals in yeast and flowers suggests that yeast‐insect communication may have contributed to the evolution of insect‐mediated pollination in flowers.

Identification and susceptibility of clinical isolates of Candida spp. to killer toxins.

Although invasive infections and mortality caused by Candida species are increasing among compromised patients, resistance to common antifungal agents is also an increasing problem. We analyzed 60 yeasts isolated from patients with invasive candidiasis using a PCR/RFLP strategy based on the internal transcribed spacer (ITS2) region to identify different Candida pathogenic species. PCR analysis was performed from genomic DNA with a primer pair of the ITS2-5.8S rDNA region. PCR-positive samples were characterized by RFLP. Restriction resulted in 23 isolates identified as C. albicans using AlwI, 24 isolates as C. parapsilosis using RsaI, and 13 as C. tropicalis using XmaI. Then, a group of all isolates were evaluated for their susceptibility to a panel of previously described killer yeasts, resulting in 75% being susceptible to at least one killer yeast while the remaining were not inhibited by any strain. C. albicans was the most susceptible group while C. tropicalis had the fewest inhibitions. No species-specific pattern of inhibition was obtained with this panel of killer yeasts. Metschnikowia pulcherrima, Pichia kluyveri and Wickerhamomyces anomalus were the strains that inhibited the most isolates of Candida spp.

Impact of storage conditions on fungal community composition of green coffee beans Coffea arabica L. stored in jute sacks during 1year.

The purpose of this study was to evaluate the effect of warehouse storage conditions on the composition of the fungal community of green coffee beans (GCB) that were stored in jute sacks for 1year. Molecular characterization of the fungal community composition and population dynamics obtained by Q-PCR, CE-SSCP (Simpson's diversity index D) and Illumina MiSeq sequencing indicated that Saccharomycetales dominated during the first 6months of storage period with species as Meyerozyma guilliermondii and Pichia kluyveri. However, after 6months of storage, the filamentous genus Wallemia became dominant. Principal components analysis correlated this fungal dynamic with storage conditions and other variables as chromaticity (colour), water activity, moisture content, reducing sugars concentration, fungal infection and ochratoxin A production. This study demonstrated that GCB stored in jute sacks after 6months of storage lead to fungal population dynamics, decreased chromaticity in GCB by bleaching and, then, affected overall quality. Storage plays an important role in the quality evolution during the handling of the GCB. In this context, the composition of the microbial community could be considered a marker to assess the trade value of the coffee beans.

Identification of uncommon oral yeasts from cancer patients by MALDI-TOF mass spectrometry

BackgroundOpportunistic infections due to Candida species occur frequently in cancer patients because of their inherent immunosuppression. The aim of the present study was to investigate the epidemiology of yeast species from the oral cavity of patients during treatment for oncological and haematological malignancies.MethodsMALDI-TOF was performed to identify yeasts isolated from the oral cavity of 350 cancer patients. Moreover, antifungal susceptibility testing was performed in according to CLSI guidelines (M27-A3).ResultsAmong 162 yeasts and yeast-like fungi isolated from the oral cavity of cancer patients, Candida albicans was the most common species (50.6%), followed by Candida glabrata (24.7%), Pichia kudriavzevii (Candida krusei (9.9%)), Candida tropicalis (4.3%), Candida dubliniensis (3.7%), Kluyveromyces marxianus (Candida kefyr (3.7%)) and Candida parapsilosis (1%). In addition, uncommon yeast species i.e., Saprochaete capitata, Saccharomyces cerevisiae, Clavispora lusitaniae (C. lusitaniae) and Pichia kluyveri (C. eremophila) were recovered from oral lesions. Oral colonization by C. albicans, non-albicans Candida species and uncommon yeasts were as follow; 55%, 44% and 1%, whereas oral infection due to C. albicans was 33.3%, non-albicans Candida species 60.6%, and uncommon yeasts 6.1%. Poor oral hygiene and xerostomia were identified as independent risk factors associated with oral yeast colonization. The overall resistance to fluconazole was 11.7% (19/162). Low MIC values were observed for anidulafungin for all Candida and uncommon yeast species.ConclusionsThis current study provides insight into the prevalence and susceptibility profiles of Candida species, including emerging Candida species and uncommon yeasts, isolated from the oral cavity of Iranian cancer patients. The incidence of oral candidiasis was higher amongst patients with hematological malignancies. The majority of oral infections were caused by non-albicans Candida species which were often more resistant to anti-fungal agents. Our findings suggest that anidulafungin should be used as antifungal of choice for prophylaxis in clinically high-risk patients with documented oral colonization or infection.

Biodegradation and detoxification of aliphatic and aromatic hydrocarbons by new yeast strains

Seeking new efficient hydrocarbon-degrading yeast stains was the main goal of this study. Because microorganisms are greatly affected by the environmental factors, the biodegradation potentiality of the microorganisms varies from climatic area to another. This induces research to develop and optimize the endemic organisms in bioremediation technology. In this study, 67 yeast strains were tested for their growth potentiality on both aliphatic and aromatic hydrocarbons. The most efficient six strains were identified using sequence analysis of the variable D1/D2 domain of the large subunit 26S ribosomal DNA. The identity of these strains was confirmed as Yamadazyma mexicana KKUY-0160, Rhodotorula taiwanensis KKUY-0162, Pichia kluyveri KKUY-0163, Rhodotorula ingeniosa KKUY-0170, Candida pseudointermedia KKUY-0192 and Meyerozyma guilliermondii KKUY-0214. These species are approved for their ability to degrade both aliphatic and aromatic hydrocarbons for the first time in this study. Although, all of them were able to utilize and grow on both hydrocarbons, Rhodotorula taiwanensis KKUY-0162 emerged as the best degrader of octane, and Rhodotorula ingeniosa KKUY-170 was the best degrader of pyrene. GC-MS analysis approved the presence of many chemical compounds that could be transitional or secondary metabolites during the utilization of the hydrocarbons. Our results recommend the application of these yeast species on large scale to approve their efficiency in bioremediation of oil-contamination of the environment. Using these yeasts, either individually or in consortia, could offer a practical solution for aquatic or soil contamination with the crude oil and its derivatives in situ.