Phenotypic and molecular identification of yeast species associated with Spanish blue-veined Cabrales cheese

The diversity of microbial communities in Chinese milk fan and their effects on volatile organic compound profiles

Milk fan is a cheese-like fermented milk product produced in Yunnan Province, China. In this study, we characterized the microbial communities of milk fan from 6 distinct geographical origins and investigated their generation of volatile organic compounds (VOC). The microbial communities found in all milk fan samples were dominated by Lactococcus, Lactobacillus, and Raoultella bacteria and Rhodotorula, Torulaspora, and Candida fungi. Samples from the Kunming and Weishan regions had greater bacterial richness, and samples from Xizhou had greater fungal community richness. Sixty prominent VOC (i.e., those having odor activity values ≥1), including esters, acids, alcohols, aldehydes, ketones, and aromatic compounds, were identified by gas chromatography-mass spectrometry analysis of milk fan samples. Pearson correlation analysis revealed that Lactobacillus, Rhodotorula, Lodderomyces, and Debaryomyces had significant correlations with various VOC, revealing a total of 13 compounds that are characteristic of the odor of milk fan. These bacteria and fungi are therefore identified as functional microorganisms that collectively create the complex VOC profile of milk fan. This study provides a comprehensive overview of the microbial community of milk fan and demonstrates its contribution to the unique aroma profile of this fermented milk product.

In vitro virulence determinants, comparative pathogenicity of Diutina (Candida) mesorugosa clinical isolates and literature review of the D. rugosa complex

Opportunistic mycoses by yeasts have increased considerably in the last three decades. Although Candida albicans is considered one of the most important causes of nosocomial infections, there is a recent shift to non-albicans Candida species as the most frequently isolated yeasts in particular risk groups. Diutina rugosa (formerly Candida rugosa) is a complex that includes four species: D. rugosa sensu stricto, D. neorugosa, D. pseudorugosa, and D. mesorugosa, and they are estimated to represent 0.2% of all Candida clinical isolates. In this study, we analyze nine clinical isolates of D. mesorugosa with focus on the virulence determinants and pathogenicity of the species by means of a Galleria mellonella survival model. Overall, we detected very strong aspartyl-protease and esterase activities. In contrast, both DNase and hemolysin activities were evident in only two of the isolates. None of the isolates was positive for phospholipase activity. All isolates studied were able to form biofilm after 72 h of incubation in a robust manner when compared with the C. albicans strain used as control. Susceptibility testing showed minimum inhibitory concentrations (MICs) ≤1 µg/mL for amphotericin B in all isolates tested. Eight out of nine of the isolates had MICs ≤2 µg/mL for fluconazole. All isolates were resistant to both anidulafungin and caspofungin (MICs ≥1 µg/mL). We found a significant difference (P < 0.0001) amongst the survival curves for the different D. mesorugosa isolates in the Galleria mellonella survival model. Strains HPM309 and H259 produced an acute infection and exhibited the highest virulence, whereas the D. mesorugosa isolates 99-480 and DM17 proved to be the less virulent strains.

Effect of different starter cultures on chemical and microbial parameters of buckwheat honey fermentation

The aim of this study was to analyze the microbiology of buckwheat honey fermentation inoculated with different starter cultures by culturing and PCR-DGGE, taking as a model for comparison a spontaneously fermented batch. The inoculants tested were (i) cider lees (from a cider factory), (ii) sourdough (from a bakery), and (iii) a commercial Saccharomyces cerevisiae strain. The results of the culturing and culture-independent techniques agreed well and detected the same dominant species along the fermentations. Our results suggest that S. cerevisiae strains, which constituted a majority population in all batches including the uninoculated one, carried out the fermentations. The highest microbial diversity was found at the beginning of the fermentation in the uninoculated batch; this contained in addition to S. cerevisiae bacteria (Paracoccus sp., Staphylococcus sp., and Bacillus sp.) and yeast (Candida sp.) species. Candida sp. was also common in batches inoculated with sourdough and cider lees cultures. Lactobacillus species were found throughout the fermentation of the sourdough-inoculated batch. Basic chemical analysis and testing trials demonstrated that the overall sensory acceptance of the four meads were highly similar. Yeast and bacteria isolated in this study could serve as a source of technologically relevant microorganisms for mead production.

[Yeast microbiota in artisanal cheeses from Corrientes, Argentina]

The artisanal cheese from Corrientes (from the Spanish acronym QAC-Queso Artesanal de Corrientes/Artisanal Cheese from Corrientes) is a soft cheese elaborated with raw cow milk and an artisanal coagulant agent. Lactic bacteria contitute the main flora of this cheese although yeasts are also present in high quantities as secondary microbiota and might play a relevant role in cheese ripening. The aim of this work was to evaluate yeast occurrence during QAC elaboration and ripening, and the effect of seasonal variation. Yeasts were isolated and purified from raw materials and cheese at different ripening stagesl elaborated during the different seasons. Yeast sample counts were in the order of 10³ - 10⁷UFC/ml o UFC/g. Ninety yeast strains were classified: 9 from milk, 28 from the coagulant agent, 10 from curd and 43 from cheese. Candida predominated in milk samples while other yeast genera had low incidence. Candida also predominated in the coagulant agent samples, followed by genera Myxozyma and Debaryomyces. The isolates obtained from cheese belonged to the same genera predominating in the coagulant agent, and showed the same order of prevalence.

Molecular Identification of Yeasts and Lactic Acid Bacteria Involved in the Production of Beninese Fermented Food Degue

Background:

Traditional Beninese fermented food Degue is widely consumed in Benin and other countries in West Africa. It was originally made from milk and millet flour, but currently other cereals are used as well. Nowadays, Degue production occurs by spontaneous fermentation in individual households and information about the microorganisms involved is currently limited.

Objective:

The microbiota of Degue from Benin has not been studied so far, but its growing production in the country sets a demand for revealing the biodiversity of the microbial population involved in the fermentation process in order to take future steps for development of industrial technology and offer products with improved quality and safety.

Method:

In the present study, yeast and lactic acid bacteria from raw materials for Degue production and from several Degue products were isolated and identified by molecular methods including RFLP and ITS1-5.8S-ITS2 rRNA gene sequence analysis in yeasts, and 16S rRNA gene sequence analysis in lactic acid bacteria.

Results:

Lactic acid bacteria isolates were assigned to eight species within the generaLactobacillus,Enterococcus,Pediococcus,StreptococcusandWeisella. Four species of yeasts were found in Degue:Cyberlyndnera fabianii,Candida glabrata,Kluyveromyces marxianus, andMeyerozyma caribbica.

Conclusion:

The microbial population revealed is unique to Beninese Degue and needs further characterization for development of defined starter cultures.

Application of ISSR-PCR for rapid strain typing of Debaryomyces hansenii isolated from dry-cured Iberian ham

Yeast populations of dry-cured Iberian ham isolated from seven industries in the province of Badajoz were characterized by ISSR-PCR using the (CAG)4 primer and PCR-RFLP of the ITS1-5.8S rRNA-ITS2 fragment, and identified by DNA sequencing. A total of 242 isolates were analyzed, indicating the primary species present was Debaryomyces hansenii at 80.9% of the isolates followed by Candida zeylanoides at 10.3% of the isolates. The remainders of isolates were identified as Yamadazyma triangularis, Sporobolomyces roseus, Meyerozyma guilliermondii, Rhodotorula slooffiae, and Cryptococcus victoriae. The ISSR-PCR method was a fast and reliable method which was able to discriminate species at a level comparable to restriction analyses of the ITS1-5.8S rRNA-ITS2 region. This method allowed for strain typing of D. hansenii, yielding 29 different PCR patterns within 196 isolates. Moreover, ISSR-PCR using the (CAG)4 primer indicated that this technique could be a promising tool for rapid discrimination of yeast starter cultures and spoilage species in dry-cured Iberian ham.

Systematic review and new insights into the molecular characterization of the Candida rugosa species complex

Recently, Candida rugosa was characterized as a species complex comprising four taxa: C. rugosa sensu stricto, Candida pseudorugosa, Candida neorugosa and Candida mesorugosa. Although considered relatively rare, several clusters of candidemia due to C. rugosa complex had been reported presenting mortality rates close to 70%. In this work we discuss the systematization, phenotyping and molecular methods based on internal transcribed spacer region (ITS) sequencing and proteomic analyses for species identification, as well as clinical aspects of the C. rugosa complex. We performed a Bayesian phylogenetic analysis using 72 ITS sequences representative of C. rugosa complex isolates and related species within the genus. Biochemical, morphological and MALDI-TOF MS analyses were processed with C. rugosa complex type strains and related species isolates. We described that the phylogeny showed four distinct clades inferred with high posterior probabilities, corresponding to the four species within the C. rugosa complex, excluding C. pararugosa. Biochemical and morphological aspects distinguished only C. rugosa sensu stricto but were not sufficient to accurately identify species within the rest of the complex. Protein spectrum profiles differentiated all reference strains from different species analyzed. To our knowledge, we presented the first phylogenetic analysis using a large collection of ITS sequences as well as proteomic profiles generated from isolates of the C. rugosa complex and related species that can enlighten systematics, diagnostics and clinical research fields.

Saccharomyces unisporus: Biotechnological Potential and Present Status

 The yeast species of the Saccharomyces genus have a long history of traditional applications and beneficial effects. Among these presence of the Saccharomyces unisporus has been documented in various dairy products and has become a subject of interest and great importance. S. unisporus has shown a significant role in the ripening of cheese and production of fermented milk products such as kefir and koumiss. The absence of pseudohyphae during the life cycle of S. unisporus is an indication of nonpathogenicity. Significance has been laid on the presence of S. unisporus in food-grade products and a close proximity of S. unisporus to S. florentinus and both of these species are accepted by the International Dairy Federation and the European Food and Feed Cultures Association for food and feed applications. Since over the years, S. unisporus has already become a part of various dairy products, S. unisporus can be considered as a potential candidate for generally regarded as safe status. S. unisporus has the capacity to convert ketoisophorone to levodione, which is an important pharmaceutical precursor. S. unisporus are considered as the potential producers of farnesol which eventually controls filamentation of pathogenic microorganisms. Apart from that, S. unisporus produces certain omega unsaturated fatty acids which combat diseases. Henceforth, the areas which S. unisporus can be possibly exploited for its useful intermediates are the enzymes and fatty acids it produces. In this context, this review attempts to describe and discuss the ubiquity of S. unisporus in food products, cellular composition, regulatory pathways, and its synthesis of fatty acids and enzymes.

Candida cabralensis sp. nov., a yeast species isolated from traditional Spanish blue-veined Cabrales cheese

Three yeast strains, 1AD8T, 3AD15 and 3AD23, belonging to a previously unknown yeast species were isolated from two independent batches of the Spanish blue-veined Cabrales cheese, a traditional cheese manufactured without the addition of starter and mould cultures. Physiological characterization revealed that the unknown yeast is not fermentative and does not assimilate lactose; rather it assimilates dl-lactic acid and ethanol, major end products of lactic acid bacteria metabolism in cheese. The novel yeast is anamorphic. Phylogenetic tree reconstruction based on nucleotide sequence comparison of the D1/D2 region of the 26S rRNA gene showed that Pichia terricola and Pichia fermentans are the closest relatives of the unknown species. The name Candida cabralensis sp. nov. is proposed, and the isolate 1AD8T (=CECT 13027T =CBS 11679T) is the type strain of this novel taxon.

Occurrence and dominance of yeast species in naturally fermented milk from the Tibetan Plateau of China

To determine which yeasts are present in the naturally fermented milks of China, 69 samples made by the nomads of Tibet were collected from the Tibetan Plateau in China. From these samples, 225 strains of yeast were isolated and identified using conventional microbiological analysis and gene sequencing analysis of the D1/D2 domain of the large subunit (26S) ribosomal DNA. The results showed that the total concentration of yeasts in these samples ranged from 5.01 to 8.97 log10 colony-forming units (CFU)/mL (6.91 ± 1.02 log10 CFU/mL; mean ± SD). The number of cultivable yeasts was higher in the samples from Qinghai (7.55 ± 0.75 log10 CFU/mL) than those from Tibet (6.21 ± 0.79 log10 CFU/mL, P < 0.05). Moreover, there were 15 phylotypes in these 69 samples. Among these phylotypes, Kluyveromyces marxianus (49.3%, frequency percentage), Saccharomyces cerevisiae (62.3%), and Pichia fermentans (46.4%) appeared frequently and can be considered the most common culturable species in naturally fermented milk products. Traditional fermented Mongolian cow milk featured a wide diversity of yeast species, including Issatchenkia orientalis , Kazachstania unisporus , Rhodotorula mucilaginosa , Candida pararugosa , Torulaspora delbrueckii , Geotrichum sp., Kazachstania unisporus , Geotrichum fragrans , Debaryomyces hansenii , Yarrowia lipolytica , Trichosporon gracile , and Pichia membranifaciens . This study provides new data on yeast composition in naturally fermented milk and shows the yeast biodiversity of fermented milk products from the Tibetan Plateau of China.