Isolation, identification, and tolerance analysis of yeast during the natural fermentation process of Sidamo coffee beans.

Yeast, which plays a pivotal role in the brewing, food, and medical industries, exhibits a close relationship with human beings. In this study, we isolated and purified 60 yeast strains from the natural fermentation broth of Sidamo coffee beans to screen for indigenous beneficial yeasts. Among them, 25 strains were obtained through morphological characterization on nutritional agar medium from Wallerstein Laboratory (WL), with molecular biology identifying Saccharomyces cerevisiae strain YBB-47 and the remaining 24 yeast strains identified as Pichia kudriavzevii. We investigated the fermentation performance, alcohol tolerance, SO2 tolerance, pH tolerance, sugar tolerance, temperature tolerance, ester production capacity, ethanol production capacity, H2S production capacity, and other brewing characteristics of YBB-33 and YBB-47. The results demonstrated that both strains could tolerate up to 3% alcohol by volume at a high sucrose mass concentration (400 g/L) under elevated temperature conditions (40 ℃), while also exhibiting a remarkable ability to withstand an SO2 mass concentration of 300 g/L at pH 3.2. Moreover, S. cerevisiae YBB-47 displayed a rapid gas production rate and strong ethanol productivity. whereas P. kudriavzevii YBB-33 exhibited excellent alcohol tolerance. Furthermore, this systematic classification and characterization of coffee bean yeast strains from the Sidamo region can potentially uncover additional yeasts that offer high-quality resources for industrial-scale coffee bean production.

High Potential of Pichia kluyveri and Other Pichia Species in Wine Technology.

The surfaces of grapes are covered by different yeast species that are important in the first stages of the fermentation process. In recent years, non-Saccharomyces yeasts such as Torulaspora delbrueckii, Lachancea thermotolerans, Metschnikowia pulcherrima, and Pichia kluyveri have become popular with regard to winemaking and improved wine quality. For that reason, several manufacturers started to offer commercially available strains of these non-Saccharomyces species. P. kluyveri stands out, mainly due to its contribution to wine aroma, glycerol, ethanol yield, and killer factor. The metabolism of the yeast allows it to increase volatile molecules such as esters and varietal thiols (aroma-active compounds), which increase the quality of specific varietal wines or neutral ones. It is considered a low- or non-fermentative yeast, so subsequent inoculation of a more fermentative yeast such as Saccharomyces cerevisiae is indispensable to achieve a proper fermented alcohol. The impact of P. kluyveri is not limited to the grape wine industry; it has also been successfully employed in beer, cider, durian, and tequila fermentation, among others, acting as a promising tool in those fermentation processes. Although no Pichia species other than P. kluyveri is available in the regular market, several recent scientific studies show interesting improvements in some wine quality parameters such as aroma, polysaccharides, acid management, and color stability. This could motivate yeast manufacturers to develop products based on those species in the near future.

Population genomics shows no distinction between pathogenic Candida krusei and environmental Pichia kudriavzevii: One species, four names.

We investigated genomic diversity of a yeast species that is both an opportunistic pathogen and an important industrial yeast. Under the name Candida krusei, it is responsible for about 2% of yeast infections caused by Candida species in humans. Bloodstream infections with C. krusei are problematic because most isolates are fluconazole-resistant. Under the names Pichia kudriavzevii, Issatchenkia orientalis and Candida glycerinogenes, the same yeast, including genetically modified strains, is used for industrial-scale production of glycerol and succinate. It is also used to make some fermented foods. Here, we sequenced the type strains of C. krusei (CBS573T) and P. kudriavzevii (CBS5147T), as well as 30 other clinical and environmental isolates. Our results show conclusively that they are the same species, with collinear genomes 99.6% identical in DNA sequence. Phylogenetic analysis of SNPs does not segregate clinical and environmental isolates into separate clades, suggesting that C. krusei infections are frequently acquired from the environment. Reduced resistance of strains to fluconazole correlates with the presence of one gene instead of two at the ABC11-ABC1 tandem locus. Most isolates are diploid, but one-quarter are triploid. Loss of heterozygosity is common, including at the mating-type locus. Our PacBio/Illumina assembly of the 10.8 Mb CBS573T genome is resolved into 5 complete chromosomes, and was annotated using RNAseq support. Each of the 5 centromeres is a 35 kb gene desert containing a large inverted repeat. This species is a member of the genus Pichia and family Pichiaceae (the methylotrophic yeasts clade), and so is only distantly related to other pathogenic Candida species.

Yeast communities of primary and secondary peat swamp forests in southern Thailand.

Khanthuli peat swamp forest (PSF) is one of a few fertile peat swamp forests that remain in Thailand. It is composed of primary PSF and some areas which have been degraded to secondary PSF due to drought, wildfires and land conversion, which have resulted in a decrease in peat layers and change in the species of the plant community. In this study, diversity of yeasts in peat from both primary and secondary PSF areas of the Khanthuli PSF was determined based on culture-dependent approaches, using dilution plate and enrichment techniques. A total of 66 yeast isolates were identified by the analysis of sequence similarity of the D1/D2 region of the large subunit rRNA gene or the combined analysis of sequence of the D1/D2 region and internal transcribed spacer region and confirmed by phylogenetic analysis of the D1/D2 region to belong to 22 known yeast species and six potential new species in the genera Candida (Kurtzmaniella, Lodderomyces, Ogataea, Pichia and Yamadazyma clades), Clavispora, Cyberlindnera, Galactomyces, Hanseniaspora, Metschnikowia, Saturnispora, Schwanniomyces, Cryptotrichosporon, Pichia, Curvibasidium, Papiliotrema, Rhodotorula, and Saitozyma. The most prevalent yeasts in the primary PSF were Cyberlindnera subsufficiens and Galactomyces candidus, while Saitozyma podzolica was the most frequently found in peat from the secondary PSF. Common yeast species in both, primary and secondary PSF, were Cy. subsufficiens, G. candidus and Rhodotorula mucilaginosa.

Impact of seasonality and environmental conditions on yeast diversity from camel's milk collected in Algeria.

During this study, we characterized the seasonality's impact and environmental conditions on the yeast diversity from raw camel's milk collected in Algeria. The yeast counts were estimated to 3.55 × 102 CFU mL-1, with a maximum of 6.3 × 102 CFU mL-1. The yeasts were categorized phenotypically by API 20C AUX, MALDI-TOF and genetically by sequencing 26S rDNA and ITS1-5.8S-ITS2. The rDNA sequencing approaches revealed 12 species including unusual ones such as Trichosporon asahii, Pichia fermentans, Millerozyma farinosa, Pichia galeiformis, Candida tartarivorans and Pichia manshurica. The most dominant species were T. asahii (23%), P. fermentans (19%) and Rhodotorula mucilaginosa (14%). The high occurrence and large diversity were registered in samples collected during the autumn season, in the semi-arid and arid highlands regions with 0.66 × 103 CFU mL-1 and 0.51 × 103 CFU mL-1, respectively. Interestingly, T. asahii, R. mucilaginosa, P. fermentans, C. parapsilosis and C. zeylanoides were detected during both spring and autumn.

Identification of Novel Endophytic Yeast Strains from Tangerine Peel.

Seven endophytic yeast strains were isolated from tangerine peel (Citrus reticulata Blanco) and genotyped through clustering with D1/D2 and ITS1-5.8S-ITS2 sequences from GenBank. Phenotypic characteristics were obtained through commercial kits and through assisted species identification. Indole-3-acetic acid (IAA) production by the yeast strains was assessed using Salkowski reagent and High-Performance Liquid chromatography (HPLC). The growth-promoting effects of the yeast were evaluated using the 'ragdoll' method. CRYb1, CRYb2 and CRYb7 isolates were identified as the closest species Hanseniaspora opuntiae. CRYb3 was identified as Pichia kluyveri. CRYb4, CRYb5 and CRYb6 were identified as Meyerozyma guilliermondii. CRYb1, CRYb5, CRYb6 and CRYb7 were found to be capable of IAA production. The most promising yeast strains now require further evaluation for their ability to promote plant growth in vitro and in vivo. These data increase our knowledge of the distribution and biological properties of endophytic yeast. This is important information that will be required to fully harness the growth-promoting properties of yeast strains.

Screening of new yeast Pichia manchurica for arabitol production.

Arabitol has several applications in food and pharmaceutical industries as a natural sweetener, dental caries inhibitor, and texturing agent. Newly isolated yeast strains from seawater, sugarcane plantation soil samples, and Zygosaccharomyces rouxii 2635 from MTCC were tested for arabitol production. The yield of arabitol was found to be higher in seawater isolate (24.6 g L-1 ) compared to two soil isolates (22.5 g L-1 ) and Z. rouxii (19.4 g L-1 ). Based on ITS 26S rDNA sequence analysis, the seawater isolate was identified as Pichia manchurica. In the present study, the effect of different substrates, trace elements, nitrogen sources, pH, and temperature on arabitol production was examined. Three different carbon sources viz. glucose, arabinose, and galactose were studied. Glucose was determined to be the best substrate for arabitol production (27.6 g L-1 ) followed by arabinose (13.7 g L-1 ) and galactose (7.7 g L-1 ). Maximum production of arabitol was observed at pH 6.0 (34.7 g L-1 ). In addition, arabitol production was high (35.7 g L-1 ) at temperature of 30 °C. Among the different concentrations of ammonium sulfate tested (3, 4.5, 6, 7.5, and 9 g L-1 ) concentration of 6 g L-1 resulted in higher arabitol Individual metal ions had no effect on arabitol production by this strain as compared to control. Results obtained in this study identify ways for improved arabitol production with natural isolates using microbial processes.

Candida infanticola and Candida spencermartinsiae yeasts: Possible emerging species in cancer patients.

Opportunistic infections due to Candida species occur frequently in intensive care settings. We investigated the prevalence of Candida species among 65 clinical specimens obtained from 200 cancer patients by phenotypic and molecular (ITS sequencing and AFLP) methods. Among the 65 yeast isolates, Candida albicans was the most commonly isolated species (n = 34, 52.3%), whereas other Candida species comprised 47.7% (n = 31) and consisted of Candida glabrata (n = 14, 21.5%), Candida tropicalis (n = 5, 7.7%) and uncommon Candida species (n = 12, 18.5%) such as Candida pelliculosa (n = 3, 4.6%), Pichia kudriavzevii (= Candida krusei, n = 2, 3.1%), Candida orthopsilosis (n = 2, 3.1%), Candida parapsilosis (n = 1, 1.5%), Candida infanticola (n = 2, 3.1%), Candida spencermartinsiae (n = 1, 1.5%), and Kluyveromyces marxianus (=Candida kefyr, n = 1, 1.5%). Candida infanticola and Candida spencermartinsiae were recovered from oral lesions of cancer patients. Matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) easily confirmed these isolates as less common Candida isolates (4.6%). The in vitro antifungal susceptibilities of C. spencermartinsiae and the two strains of C. infanticola were determined according to CLSI guidelines (M27-A3). MIC results among these isolates showed they were susceptible to isavuconazole, posaconazole and voriconazole, however, fluconazole and caspofungin had high MIC values. These Candida species that may occur more commonly in infections remain unnoticed using commonly used phenotypical methods in routine microbiology laboratories. MALDI-TOF MS proved to be a more fast and robust diagnostic technique for identification of the yeasts isolated from different clinical specimens of cancer patients.

Low-pH production of d-lactic acid using newly isolated acid tolerant yeast Pichia kudriavzevii NG7.

Lactic acid is a platform chemical for the sustainable production of various materials. To develop a robust yeast platform for low-pH production of d-lactic acid (LA), an acid-tolerant yeast strain was isolated from grape skins and named Pichia kudriavzevii NG7 by ribosomal RNA sequencing. This strain could grow at pH 2.0 and 50°C. For the commercial application of P. kudriavzevii NG7 as a lactic acid producer, the ethanol fermentation pathway was redirected to lactic acid by replacing the pyruvate decarboxylase 1 gene (PDC1) with the d-lactate dehydrogenase gene (d-LDH) derived from Lactobacillus plantarum. To enhance lactic acid tolerance, this engineered strain was adapted to high lactic acid concentrations, and a new transcriptional regulator, PAR1, responsible for acid tolerance, was identified by whole-genome resequencing. The final engineered strain produced 135 g/L and 154 g/L of d-LA with productivity over 3.66 g/L/hr at pH 3.6 and 4.16 g/L/hr at pH 4.7, respectively.

Pichia nanzhaoensis sp. nov. and Pichia paraexigua f.a., sp. nov., two yeast species isolated from rotting wood.

Four yeast strains were isolated from rotting wood samples collected in the Baotianman Nature Reserve in Henan Province, Central China. On the basis of sequence analysis of the D1/D2 domains of the large subunit rRNA gene and the internal transcribed spacer regions, they were suggested to be two novel species of the genus Pichia. Pichia nanzhaoensis sp. nov. produces one to four spherical ascospores per ascus, and is most closely related to Candida pseudolambica. Pichia paraexigua f.a., sp. nov. is a sister taxa to Pichia exigua, but the formation of ascospores was not observed on various sporulation media. P. nanzhaoensis sp. nov. can weakly assimilate inulin, whereas P. paraexigua sp. nov. can weakly assimilate d-glucosamine. The type strain of Pichia nanzhaoensis is NYNU 178136T (=CICC 33279T=CBS 15346T) and the type strain of Pichia paraexigua is NYNU 178135T (=CICC 33278T=CBS 15237T).

Description of Komagataella mondaviorum sp. nov., a new sibling species of Komagataella (Pichia) pastoris.

Five methylotrophic strains (UCDFST 71-1024T, UCDFST 54-11.16, UCDFST 54-11.141, UCDFST 68-967.1 and UCDFST 74-1030) from the Phaff Yeast Culture Collection (University of California Davis, USA) that were originally designated as Pichia pastoris were found to represent a novel Komagataella species. Strains of Komagataella mondaviorum sp. nov. UCDFST 71-1024T(type strain) = CBS 15017, UCDFST 54-11.16, UCDFST 54-11.141, UCDFST 68-967.1, and UCDFST 74-1030 were isolated in USA, respectively, from cottonwood tree Populus deltoides in 1971 (Davis, CA), slime flux of Quercus sp. in 1954 (CA), exudate of black oak Q. kelloggii in 1954 (Central Sierra Nevada. CA), dry frass from Salix sp. in 1968 (Soleduck Road, Olympic National Park, WA) and from flux of hackberry tree Celtis sp. in 1974 (CA). The new species was differentiated from Komagataella kurtzmanii, Komagataella pastoris, Komagataella phaffii, Komagataella populi, Komagataella pseudopastoris and Komagataella ulmi by divergence in gene sequences for D1/D2 LSU rRNA, ITS1-5.8S-ITS2, RNA polymerase subunit I and translation elongation factor-1α. Komagataella mondaviorum sp. nov. is registered in MycoBank under MB 821789.

Enhancement of thermoalkaliphilic xylanase production by Pichia pastoris through novel fed-batch strategy in high cell-density fermentation.

BACKGROUND: Xylanase degrades xylan into monomers of various sizes by catalyzing the endohydrolysis of the 1,4-ß-D-xylosidic linkage randomly, possessing potential in wide industrial applications. Most of xylanases are susceptible to be inactive when suffering high temperature and high alkaline process. Therefore, it is necessary to develop a high amount of effective thermoalkaliphilic xylanases. This study aims to enhance thermoalkaliphilic xylanase production in Pichia pastoris through fermentation parameters optimization and novel efficient fed-batch strategy in high cell-density fermentation. RESULTS: Recombinant xylanase activity increased 12.2%, 7.4%, 12.0% and 9.9% by supplementing the Pichia pastoris culture with 20 g/L wheat bran, 5 mg/L L-histidine, 10 mg/L L-tryptophan and 10 mg/L L-methionine in shake flasks, respectively. Investigation of nutritional fermentation parameters, non-nutritional fermentation parameters and feeding strategies in 1 L bioreactor and 1 L shake flask revealed that glycerol and methanol feeding strategies were the critical factors for high cell density and xylanase activity. In 50 L bioreactor, a novel glycerol feeding strategy and a four-stage methanol feeding strategy with a stepwise increase in feeding rate were developed to enhance recombinant xylanase production. In the initial 72 h of methanol induction, the linear dependence of xylanase activity on methanol intake was observed (R2 = 0.9726). The maximum xylanase activity was predicted to be 591.2 U/mL, while the actual maximum xylanase activity was 560.7 U/mL, which was 7.05 times of that in shake flask. Recombinant xylanase retained 82.5% of its initial activity after pre-incubation at 80 °C for 50 min (pH 8.0), and it exhibited excellent stability in the broad temperature (60-80 °C) and pH (pH 8.0-11.0) ranges. CONCLUSIONS: Efficient glycerol and methanol fed-batch strategies resulting in desired cell density and xylanase activity should be applied in other P. pastoris fermentation for other recombinant proteins production. Recombinant xylanases with high pH- and thermal-stability showed potential in various industrial applications.

Pichia chibodasensis sp. nov., isolated in Indonesia.

Three strains (14Y260T, 14Y268 and 14Y276) of xylose-assimilating yeasts were isolated from decayed wood and soil collected in West Java in Indonesia. A phylogenetic analysis was performed based on the sequences of the D1/D2 domains of LSU, SSU and EF-1α, and the three strains were found to belong to the genus Pichia. The morphological, biochemical, physiological and chemotaxonomic characteristics indicated that these strains were distinct from other closely related species. Strains 14Y260T, 14Y268 and 14Y276 belonged to the Pichia clade and represent a novel species, named Pichia chibodasensis sp. nov. ; The type strain is 14Y260T (=NBRC 111569T=InaCC Y1042T).

South Brazilian wines: culturable yeasts associated to bottled wines produced in Rio Grande do Sul and Santa Catarina.

A comprehensive understanding of the presence and role of yeasts in bottled wines helps to know and control the organoleptic quality of the final product. The South Region of Brazil is an important wine producer, and the state of "Rio Grande do Sul" (RS) accounts for 90% of Brazilian wines. The state of "Santa Catarina" (SC) started the production in 1975, and is currently the fifth Brazilian producer. As there is little information about yeasts present in Brazilian wines, our main objective was to assess the composition of culturable yeasts associated to bottled wines produced in RS and SC, South of Brazil. We sampled 20 RS and 29 SC bottled wines produced between 2003 and 2011, and we isolated culturable yeasts in non-selective agar plates. We identified all isolates by sequencing of the D1/D2 domain of LSU rDNA or ITS1-5.8 S-ITS2 region, and comparison with type strain sequences deposited in GenBank database. Six yeast species were shared in the final product in both regions. We obtained two spoilage yeast profiles: RS with Zygosaccharomyces bailii and Pichia membranifaciens (Dekkera bruxellensis was found only in specific table wines); and SC with Dekkera bruxellensis and Pichia manshurica. Knowledge concerning the different spoilage profiles is important for winemaking practices in both regions.

Comparison of inducible versus constitutive expression of plectasin on yields and antimicrobial activities in Pichia pastoris.

BACKGROUND: Plectasin might serve as a substitute for traditional antibiotics, but its yields and antimicrobial activities warrant further investigation. OBJECTIVE: To identify the influence of inducible versus constitutive expression of plectasin on yields and antimicrobial activities. METHODS: Through SOE-PCR, a recombinant plectasin gene was generated and inserted into inducible (pPICZαA) and constitutive (pGAPZαA) vectors in order to create Pichia pastoris GS115 strains. After 120 h of fermentation, supernatants were purified by an AKTA purifier using nickel columns. Minimal inhibitory concentration (MIC) and inhibition zone assays were performed after Tricine-SDS-PAGE. RESULTS: After 120 h of fermentation, the yield of constitutive plectasin (370 µg/ml) was much lower than that from inducible vector (880 µg/ml) (P < 0.05). However, constitutive strain reached its plateau phase faster and keep more consistent yield (P < 0.05). The MICs of inducible plectasin against Methicillin-resistant Staphylococcus aureus (MRSA) 15471118, vancomycin-resistant Enterococcus feces (VREF), and penicillin-resistant Streptococcus pneumonia (PRSP) 31355 were 64, 32, and 64 µg/ml, respectively, while those of constitutive plectasin were 4, 4, and 16 µg/ml. No significant differences were observed in antimicrobial activities between inducible and constitutive plectasin for MRSA 15471118, VREF and PRSP 31355 (all P ï¼ž 0.05). However, constitutive plectasin had a larger inhibition zone than inducible plectasin with the same mass. CONCLUSIONS: Although P. pastoris GS115 (pGAPZαA-Plectasin-GS115) had lower expression than P. pastoris GS115 (pPICZαA-plectasin-GS115), it reached the plateau phase faster, had steadier yields and showed superiority in antimicrobial activities. Therefore, pGAPZαA might be more suitable for expression of plectasin in GS115 compared with pPICZαA.

[Pichia guilliermondii Infection - A Rare Differential Diagnosis of Pulmonary Nodules]. / Pulmonale Pichia guilliermondii-Infektion - Eine seltene Differenzialdiagnose pulmonaler Rundherde.

UNLABELLED: A patient presented himself with pungent, breath-dependent right chest pain and dyspnea at rest in our emergency department. The physical examination and the ECG revealed no relevant findings. The laboratory results showed an increased CRP, leukocytosis, elevated D-dimers and a respiratory partial insufficiency. In the thoracic CT angiography unclear pulmonary nodules (PN) were seen. The bronchoscopy was macroscopically normal. In the BAL yeasts and a high proportion of immune senescence cells (CD57+) were identified. After a pulmonary wedge resection resulted histologically an epithelioid cell-granulomatous inflammation. Molecular pathological a mycelium genome, in particular Pichia guilliermondii (PC) was detected. The therapy with fluconazole was successful. PC rarely causes candidemia, increased in immunocompromised patients. In our judgement this is in Europe the first described case of PC-infection in a patient, which presented no predisposition to infection with opportunistic pathogens apart from type 2 diabetes. CONCLUSION: It should be thought of fungal infection by these pathogens group in case of unclear PN, especially in combination with possibly predisposing factors.

Pichia dushanensis sp. nov. and Hyphopichia paragotoi sp. nov., two sexual yeast species associated with insects and rotten wood.

Seven yeast strains were isolated from the gut of insect larvae and decayed wood, which were collected from three localities near Nanyang, Henan Province, China. These strains were identified as two novel species through comparison of sequences in the D1/D2 domains of the large subunit (LSU) rRNA gene and other taxonomic characteristics. Pichia dushanensis sp. nov. was closely related to species in the Pichia clade and produced one to four spheroid ascospores in a deliquescent ascus. The D1/D2 sequence of P. dushanensis sp. nov. differed from its closest relative, Issatchenkia (Pichia) sp. NRRL Y-12824, by 3.6% sequence divergence (16 substitutions and 4 gaps). The species also differed from its four closest known species, Candida rugopelliculosa, Pichia occidentalis, Pichia exigua and Candida phayaonensis, by 4.1-4.4% sequence divergence (22-24 substitutions and 0-2 gaps) in the D1/D2 sequences. Hyphopichia paragotoi sp. nov. belonged to the Hyphopichia clade, and its nearest phylogenetic neighbours were Candida gotoi, Candida pseudorhagii, Candida rhagii and Hyphopichia heimii with 3.2-4.2% sequence divergence (16-21 substitutions and 1 gap) in the D1/D2 sequences. In comparison with previously established species, H. paragotoi sp. nov. formed one hat-shaped ascospore in a persistent ascus. The type strain of P. dushanensis sp. nov. is NYNU 14658(T) ( = CICC 33049(T) = CBS 13912(T)), and the type strain of H. paragotoi sp. nov. is NYNU 14666(T) ( = CICC 33048(T) = CBS 13913(T)).

Biotechnological potential of yeast isolates from cachaça: the Brazilian spirit.

This study identified phenotypic traits appropriate for biotechnological applications of 118 yeasts isolated from cachaça distilleries. Different properties were verified: capacity to use alternative carbon sources; ability to tolerate high concentrations of sucrose, ethanol, methanol, aluminum and zinc as well as different pH values and foam production. Pichia guilliermondii and Pichia anomala strains were identified as the most promising ones for application in the second-generation biofuel industry, showing ability to grow on high glycerol concentrations. Other isolates, identified as Saccharomyces cerevisiae, produced bioethanol comparable to the industrial strains, and were therefore ideal for use in the first-generation ethanol industry. Some of these strains also showed high resistance to aluminum, as observed in sugarcane juice, and to inter-cycle washings with diluted sulphuric acid, as performed in the industrial bioethanol production process. In summary, yeast isolates from cachaça distilleries displayed robustness and phenotypic plasticity, which makes them interesting for biotechnological applications.

PUTATIVE FERROXIDASES IN THE FLAVINOGENIC YEAST PICHIA GUILLIERMONDII ARE REGULATED BY IRON ACQUISITION.

Using similarity search we identified Candida (Pichia) guilliermondii genes involved in iron acquisition. This yeast possesses at least four genes potentially coding for ferri-reductases, four genes encoding iron permeases and two genes codingforferroxidases. Identified C.(P.) guilliermondii genes encoding ferroxidases possess different patterns of expression under iron repletion conditions whereas their expression is activated under iron deficiency conditions or in mutant strains defective in regulation of iron acquisition. C.(P.) guilliermondii has no homologue of Saccharomyces cerevisiae transcriptional regulator of iron metabolism, Aft1p and possess an iron regulatory network similar to that of Candida albicans. Since most of C.(P.) guilliermondii known strains are not pathogenic, in contrast to that of C. albicans, we propose C.(P.) guilliermondii as safe and useful model for studying iron-dependent regulation of metabolism in yeasts belonging to CUG clade.

Asymmetric reduction of 4-hydroxy-2-butanone to (R)-1,3-butanediol with absolute stereochemical selectivity by a newly isolated strain of Pichia jadinii.

In this study, a novel strain of Pichia jadinii, HBY61, capable of the biocatalysis of 4-hydroxy-2-butanone (4H2B) to (R)-1,3-BD was isolated. HBY61 produced (R)-1,3-BD with high activity and absolute stereochemical selectivity (100 % e.e). Glucose and beef extract were found to be the key factors governing the fermentation, and their optimal concentrations were determined to be 84.2 and 43.7 g/L, respectively. The optimal bioconversion conditions of 4H2B catalyzed by HBY61 were pH 7.4, 30 °C, and 250 rpm with 6 % (v/v) glucose as the co-substrate. Accordingly, when 45 g/L of 4H2B was divided into three equal parts and added successively into the system at set time intervals, the maximum (R)-1,3-BD concentration reached 38.3 g/L with high yield (85.1 %) and strict 100 % enantioselectivity. Compared with previously reported yields for the biocatalytic production of (R)-1,3-BD, the use of strain HBY61 provided a high yield with excellent stereoselectivity.