Yeast Extract Peptone Dextrose Research Articles

Bactericidal Effect of Underwater Plasma Treatment on Waste Brine from Kimchi Production Process and the Evaluation of Reusability of Plasma-Treated Waste Brine in Salting Kimchi Cabbage.

Recycling waste brine from the Kimchi production process is an important environmental and industry issue. We applied an underwater plasma to reduce food-borne pathogens in the waste brine. The capillary electrodes supplied by alternating current (AC) bi-polar pulsed power were applied to treat 100 L of waste brine. The inactivation efficacy was analyzed using four different agars (Tryptic Soy Agar (TSA), Marine agar (MA), de Man Rogosa Sharpe Agar (MRS), and Yeast Extract-Peptone-Dextrose (YPD), respectively. The microbial population was reduced linearly with treatment time, irrespective of culturing medium. The inactivation followed the log-linear model (R2: 0.96-0.99). The reusability of plasma-treated waste brine (PTWB) was determined by five parameters (salinity, pH, acidity, reducing sugar, and the population of microorganisms) of salted Kimchi cabbage, and they were compared with newly made brine (NMB) and waste brine (WB), respectively. The results showed that the quality of salted Kimchi cabbage prepared by PTWB was not significantly different from that of NMB, indicating that the underwater plasma treatment is feasible to reuse waste brine in the salting process of Kimchi production.

Examining How the Fermentation Medium Influences Thiol Expression and Its Perceived Aroma in Commercial Brewing Yeast Strains.

In Saccharomyces, the IRC7 gene encodes for a cysteine S-conjugate β-lyase enzyme which can release polyfunctional thiols from their cysteinylated precursor forms, thereby promoting thiol aroma in beer. This study examined the thiol production of 10 commercial yeast strains in two different media, a hopped yeast extract-peptone-dextrose (YPD) medium and a 100% barley malt wort to explore how differences in yeast strain and medium conditions influence the release of polyfunctional thiols. 3-Sulfanylhexan-1-ol was most affected by medium conditions, and its concentrations were highest in wort fermentations. The higher nitrogen content and pH of the YPD medium relative to the wort fermentations were notable differences, and significant correlations between these variables and the extent of free thiol production were observed. A strong association existed between polyfunctional thiol concentrations and the fermentation-derived, malt, and hop-derived compounds 2-phenylethanol, β-damascenone, and β-ionone. The sensory impressions of thiol character in beer were influenced by the presence of other aromatic compounds such as esters and terpene alcohols, and aroma attributes such as "tropical" were not the most suitable for describing beers brewed with yeasts that fully express homozygous IRC7F. Sensory attributes "sweaty", "vegetal", and "overripe fruit" were more strongly associated with these strains.

Holothurin And Caspofungin-Induced Alterations In Ttoll-Like Receptor 4expression In The Vagina Of Rattus Norvegicus Wistar With Candidiasis

Abstract Toll-like receptor 4 is a marker that indicates whether or not tissues have immunological or pro-inflammatory responses. Candida albicans has the potential to aggravate the tissue that makes up the epithelium. After candidiasis, the antifungal properties of holothurin and caspofungin have the ability to block toll-like receptor 4. A total of 48 white rats Rattus norvegius Wistar were divided into four positive control groups (P1) and given topical C. albicans after being grown in yeast extract peptone dextrose in the vagina of white rats Rattus norvegius Wistar. P2 and P3 groups were given 3500 g holothurin and 140 g caspofugin topically in the vagina of animal models at 12-, 24-, and 48-hour intervals. Immunofluorescence was used to analyse the study results both quantitatively and qualitatively by attaching the imaging. After that, the data was processed using the SPSS statistical software version 23. Toll-like receptor 4 expression decreased significantly in the treatment group compared to the positive control group (p0.05). This demonstrates that holothurin (P1) and caspofungin (P2) treatments reduced toll-like receptor 4 expression in C. albicans at 0.25 and 6.375 at 12 hours, 0.62 and 3. at 24 hours, and 1.68 and 4.18 at 48 hours. The mean difference in toll-like receptor 4 expression in the positive control group, on the other hand, did not differ statistically when compared to the negative (healthy) control group. This demonstrates that the treatment group’s holothurin and caspofungin have the potential to reduce toll-like receptor 4 expression. Holothurin has a potential effect compared to caspofungin on experimental animals with candidiasis experiencing significant changes in suppressing the number of toll-like receptor 4 in vaginal epithelial tissue of Rattus norvegicus Wistar

Begerowomyces aurantius sp. nov., a novel yeast isolated from koalas' habitat in a Japanese zoological park.

Koalas are iconic mammals indigenous to Australia. These rare animals and their habitats are occasionally associated with pathogenic fungi, including species of Cryptococcus, and consequently, monitoring the mycobiota of areas inhabited by koalas is of considerable importance. In this report, we describe a novel basidiomycetous yeast isolated from a site in Kanazawa Zoo, Japan, associated with captive koalas. Swab samples were collected from koala breeding environments, from which we isolated a novel unencapsulated yeast characterized by ovoid to ellipsoidal cells (3.2-4.9 × 3.5-5 μm). These cells were observed to undergo polar budding and grow as parent bud pairs, with an optimal growth temperature of 28°C. Colonies grown on yeast extract peptone dextrose agar at 28°C have a characteristic coral pink color. On the basis of physiological, morphological, and molecular characters, the new species was placed in the genus Begerowomyces, and the name Begerowomyces aurantius JCM33898T(LSEM1333T=CBS16241T) is proposed.

P345 The relationship between virulence of Candida albicans and environmental oxygen concentration

Poster session 3, September 23, 2022, 12:30 PM - 1:30 PMObjectives Candida species are known to colonize human skins and mucous membranes, and cause candidemia under various immunosuppressive conditions. Among these Candida species, C. albicans is reported to be the most frequently isolated species, and could colonize on skins, vaginas, gastrointestinal tracts, and medical devices. Environmental factors including oxygen concentration is thought to affect the capability of colonization and virulence of Candida species; however, most previous research was performed under aerobic condition, and few research focused on hypoxic conditions imitating inside the human bodies. Given these backgrounds, we performed murine experiments by culturing C. albicans under various oxygen conditions to evaluate the effect of environmental oxygen concentration on virulence. Through our studies, we aimed to clarify the actual behavior of C. albicans in the human body.MethodsIn this study, female C57BL/6 mice, 7-8 weeks old, were used and injected via lateral tail vein to cause C. albicans dissemination. Mice were divided into 4 groups according to the pre-culture conditions: aerobic, microaerobic (5% oxygen concentration), microaerobic (1% oxygen concentration), and anaerobic. Under each oxygen condition, C. albicans was grown at 37°C for 2 days on yeast extract peptone dextrose (YPD) agar and then incubated in YPD broth for 16-24 h. After incubation, C. albicans was collected, washed, resuspended in sterile PBS, and injected into each mouse at ∼2.5 × 105 colony-forming units. In this study, one reference strain (SC5314) and one clinically isolated strain (from bloodstream infection) were used. These infected mice were euthanatized 2 or 4 days after injection, and organ (kidneys and brain) fungal burdens were evaluated.ResultsThe kidneys’ fungal burdens were significantly higher in the microaerobic groups than those in the aerobic or anaerobic groups 2 and 4 days after injection. There were no significant differences between 5% oxygen concentration pre-cultured group and 1% oxygen concentration pre-cultured group. On gross examination, disseminated lesion formations were visible in the kidneys of the microaerobic groups. Similarly, the fungal burdens of brain were significantly higher in the microaerobically pre-cultured groups than in the aerobically or anaerobically pre-cultured groups. This tendency was similar for both the reference and clinically isolated strain.ConclusionOur results indicated that C. albicans could become more virulent under hypoxia, especially under microaerobic conditions. We assumed that some virulence factors of C. albicans were elevated under microaerobic conditions. These results implicated that C. albicans could become more virulent under hypoxic conditions in human bodies. In the future, we will continue to evaluate factors related to this change in virulence and pathological analysis of infected organs.

P015 A study to demonstrate heteroresistance and tolerance to azoles in Candida tropicalis

Poster session 1, September 21, 2022, 12:30 PM - 1:30 PM Objective Candida tropicalis rarely exhibits a trailing growth phenomenon in in vitro antifungal susceptibility testing (AFST) of azoles. This phenomenon is considered as ‘sensitive’ as per current CLSI guidelines. This phenomenon has been linked to treatment failure and such isolates could either be heteroresistant (HR) or tolerant, which is known with bacteria. HR subtype (<1%) of an isogenic susceptible cell population grows at drug concentrations at least 8 times higher than the minimum inhibitory concentration (MIC). Tolerant cells (5%-90% of the population) endure antimicrobial treatment several times above MIC. Characterizing these isolates could help relate their clinical susceptibility profiles to the treatment outcome. The aim of the study was to differentiate heteroresistance and tolerance from true azole resistance in C. tropicalis clinical isolates.MethodsA total of 247 clinical isolates of C. tropicalis collected over a period of 7 months (September 2021 through March 2022) from PGIMER, Chandigarh were included in the study. Identification was done by MALDI-TOF MS and antifungal susceptibility testing to fluconazole was performed by CLSI broth microdilution method (M27-A3). Isolates exhibiting trailing growth phenomena were considered for further characterization. Cells from the trailing growth of each isolate were sub-cultured onto yeast extract peptone dextrose (YPD) agar to observe for phenotypic variations with and without fluconazole. The area under the population analysis (PAP) curve (AUC) was performed to determine the degree of heteroresistance. Yeast cells within the range of 102-105 cells/ml were spot inoculated in six replicates each onto a gradient of fluconazole (0.125-256 μg/ml) in YPD agar and incubated at 35°C for 5 days to determine the viable colony forming units (CFU).ResultsOut of the 225 fluconazole susceptible C. tropicalis isolates, 10 (4.4%) were found to exhibit a trailing growth phenomenon. A dose-response relationship showed a multimodal population distribution in these isolates with varying degrees of heteroresistance as demonstrated by area under curve that ranged from 171-1331. The heterogeneous subpopulations sampled from the growth at the highest fluconazole concentration (64 μg/ml) exhibited a similar MIC (± one 2-fold difference) as that of the parent isolate when tested individually. The heterogeneity range that determines a fold difference breakpoint of the isolates varied from 16 to >256.ConclusionAn isogenic population of cells under the effect of fluconazole could give rise to phenotypically different subpopulations. With repeated exposure to the azole drugs, these seemingly susceptible isolates can emerge as fully resistant population. Clinically, the implications include relapse, treatment failure, and persistent chronic infection, owing to which this phenomenon needs attention. Current CLSI guidelines do not provide any criteria to separately classify these isolates from the susceptible and resistant varieties. Hence a definitive cut-off is warranted to identify the HR and tolerant subtypes. The AUC-PAP method could be refined further for discriminating heteroresistance from true resistance.

Isolation of Wine Yeast from Sugar Rich Sources

A total of 21 yeasts was isolated from different sugar rich sources (date palm, pomegranate, roselle, orange, grapes and dry date palm juice) collected from different locations in West Bengal, India. All isolated yeasts were identified and differentiated based on their colony morphology and growth pattern in Yeast Extract- Peptone -Dextrose (YEPD) Agar medium. The isolates could continue to survive on the slants for up to a maximum of 6 months at 8-10°C temperature without any contamination. However, these were maintained by transferring to YEPD agar slants every four months to maintain the purity and maximum viability of cultures. Fermentation was carried out at 26±1°C temperature at total soluble solid 24oBrix and pH 4.70 in molasses medium for all different isolated yeast. The total soluble solid at the end of fermentation in molasses solution was found in the range of 9.00-20.78oBrix in all isolated yeast. The pH of the substrate was decreased (0.10-1.12) during fermentation. The cell count after complete fermentation was found in the range of 3.60×108 cfu/ml to 8.79×108 cfu/ml for all the isolated yeast. The concentration of alcohol in the molasses was observed a range from 4.21 to 13.61%. After screening or checking out the efficiency of yeasts on the basis of the highest alcohol production in molasses media, five yeasts (Y4, Y101, Y33, Y102, and Y7) were selected for wine fermentation out of 24 (new isolates 21, previous isolations Y4, Y7 and Y33) at the end of 18 days fermentation.

Determination of Optimum Conditions for Ergosterol Production by Saccharomyces cerevisiae

Ergosterol is an important provitamin in the present-day of industrial biotechnology. Seven yeast strains were obtained from the market of Basrah city and subjected to screening for their ergosterol production ability using liquid-state fermentation, the cultural conditions, and nutritional requirements for optimal production of ergosterol by Saccharomyces cerevisiae under laboratory conditions were determined. Y.6 is the best isolate of the yeast that produced ergosterol. It was identified as S. cerevisiae, with a similarity rate of 97% by using the Vitek2 device, this S. cerevisiae (Y.6) was further subjected to optimization conditions. The results showed that the best medium for production was yeast extract peptone dextrose broth. The effect of two cheaper carbon sources, molasses and date juice were investigated. Maximum ergosterol (0.55% ) was produced using a medium containing date juice, with a replacement ratio of 75%, an incubation time of 72 hours, pH 5, at a temperature of 30 °C, and an inoculation volume of 4 ml. The percentage of ergosterol was (0.47, 0.55, 0.74, 0.66, 0.68 and 0.78 %), respectively.

Production of isoquercitrin from quercetin by biotransformation using Bascillus sp. CSQ10 isolated from Camellia sinensis cultivation soils

Microorganisms are widely used to produce biologically active substances owing to their versatile ability to convert inexpensive compounds into physiologically active compounds. In this study, we isolated a microorganism capable of converting quercetin to isoquercitrin, a substance with various biological functions, from tea cultivation soils. A Bacillus strain was isolated and verified as Bacillus sp. CSQ 10 using 16sRNA gene analysis. When quercetin was fed as a substrate for Bacillus sp. CSQ10, isoquercitrin was produced through biotransformation. Furthermore, Bacillus sp. CSQ10 was able to biotransform isoquercitrin to quercetin-3-O-(6″-O-acetyl)-β-d-glucoside when the medium for biotransformation was replaced with yeast extract–peptone–dextrose (YPD) medium. Based on these findings, the biotransformation performance of Bacillus sp. CSQ10 was verified by optimizing the experimental conditions for the culture system at the laboratory scale in terms of temperature, cell density, biotransformation medium, and substrate concentration. The best biotransformation yields were achieved at 37 °C, 6.0 OD600, with YPD, and 181.0 mg/L of quercetin supply. Conclusively, 193.3 mg/L and 198.8 mg/L of isoquercitrin and quercetin-3-O-(6″-O-acetyl)-β-d-glucoside, respectively, were produced by Bacillus sp. CSQ 10 under these optimized experimental conditions.

Metabolic Plasticity of Candida albicans in Response to Different Environmental Conditions

The ubiquitous commensal Candida albicans, part of the human microbiota, is an opportunistic pathogen able to cause a wide range of diseases, from cutaneous mycoses to life-threatening infections in immunocompromised patients. Candida albicans adapts to different environments and survives long-time starvation. The ability to switch from yeast to hyphal morphology under specific environmental conditions is associated with its virulence. Using hydrogen nuclear magnetic resonance spectroscopy, we profiled the intracellular and extracellular metabolome of C. albicans kept in water, yeast extract–peptone–dextrose (YPD), and M199 media, at selected temperatures. Experiments were carried out in hypoxia to mimic a condition present in most colonized niches and fungal infection sites. Comparison of the intracellular metabolites measured in YPD and M199 at 37 °C highlighted differences in specific metabolic pathways: (i) alanine, aspartate, glutamate metabolism, (ii) arginine and proline metabolism, (iii) glycerolipid metabolism, attributable to the diverse composition of the media. Moreover, we hypothesized that the subtle differences in the M199 metabolome, observed at 30 °C and 37 °C, are suggestive of modifications propaedeutic to a subsequent transition from yeast to hyphal form. The analysis of the metabolites’ profiles of C. albicans allows envisaging a molecular model to better describe its ability to sense and adapt to environmental conditions.

Analysis of fungal dynamic changes in the natural fermentation broth of 'Hongyang' kiwifruit.

‘Hongyang’ kiwifruit (Actinidia chinensis Planch.) is an ideal kiwifruit wine variety. At present, there is no research on the dynamic changes of yeast during the natural fermentation of kiwifruit wine. In this study, a high-throughput was employed to analyze the fungal population composition and diversity in the samples cultured in yeast extract peptone dextrose (YPD) medium and enriched in the natural fermentation process of ‘Hongyang’ kiwifruit at four time points, day one (D1T), day three (D3T), day five (D5T), and day fifteen (D15T). Five hundred and eighty-two operational taxonomic units (OTUs) were obtained from 131 genera and 178 species samples. The diversity analysis results showed that in the early natural fermentation stage, the dominant species was Aureobasidium pullulans, and as natural fermentation proceeded, the genus Pichia became the dominant species. Pichia kluyveri was an important species at the later stages of natural fermentation. An analysis of the metabolic pathways shows that P. kluyveri plays an aromatic-producing role in the natural fermentation of ‘Hongyang’ kiwifruit. These results could provide a theoretical basis for the studies of kiwifruit fungal diversity and fungal changes during fermentation. The findings could fix a major deficiency in the production of kiwifruit fruit wine, which lacks a specific flavor-producing yeast species or strain.

Enhancing biofuels production by engineering the actin cytoskeleton in Saccharomyces cerevisiae

Saccharomyces cerevisiae is widely employed as a cell factory for the production of biofuels. However, product toxicity has hindered improvements in biofuel production. Here, we engineer the actin cytoskeleton in S. cerevisiae to increase both the cell growth and production of n-butanol and medium-chain fatty acids. Actin cable tortuosity is regulated using an n-butanol responsive promoter-based autonomous bidirectional signal conditioner in S. cerevisiae. The budding index is increased by 14.0%, resulting in the highest n-butanol titer of 1674.3 mg L−1. Moreover, actin patch density is fine-tuned using a medium-chain fatty acid responsive promoter-based autonomous bidirectional signal conditioner. The intracellular pH is stabilized at 6.4, yielding the highest medium-chain fatty acids titer of 692.3 mg L−1 in yeast extract peptone dextrose medium. Engineering the actin cytoskeleton in S. cerevisiae can efficiently alleviate biofuels toxicity and enhance biofuels production.

Revealing the Yeast Diversity of the Flor Biofilm Microbiota in Sherry Wines Through Internal Transcribed Spacer-Metabarcoding and Matrix-Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry.

Flor yeast velum is a biofilm formed by certain yeast strains that distinguishes biologically aged wines such as Sherry wine from southern Spain from others. Although Saccharomyces cerevisiae is the most common species, 5.8 S-internal transcribed spacer (ITS) restriction fragment length polymorphism analyses have revealed the existence of non-Saccharomyces species. In order to uncover the flor microbiota diversity at a species level, we used ITS (internal transcribed spacer 1)-metabarcoding and matrix-assisted laser desorption/Ionization time of flight mass spectrometry techniques. Further, to enhance identification effectiveness, we performed an additional incubation stage in 1:1 wine:yeast extract peptone dextrose (YPD) before identification. Six species were identified: S. cerevisiae, Pichia manshurica, Pichia membranifaciens, Wickerhamomyces anomalus, Candida guillermondii, and Trichosporon asahii, two of which were discovered for the first time (C. guillermondii and Trichosporon ashaii) in Sherry wines. We analyzed wines where non-Saccharomyces yeasts were present or absent to see any potential link between the microbiota and the chemical profile. Only 2 significant volatile chemicals (out of 13 quantified), ethanol and ethyl lactate, and 2 enological parameters (out of 6 quantified), such as pH and titratable acidity, were found to differ in long-aged wines. Although results show a low impact where the non-Saccharomyces yeasts are present, these yeasts isolated from harsh environments (high ethanol and low nutrient availability) could have a potential industrial interest in fields such as food microbiology and biofuel production.

Methods for Oxygenation of Continuous Cultures of Brewer’s Yeast, Saccharomyces cerevisiae

Maintaining steady-state, aerobic cultures of yeast in a bioreactor depends on the configuration of the bioreactor system as well as the growth medium used. In this paper, we compare several conventional aeration methods with newer filter methods using a novel optical sensor array to monitor dissolved oxygen, pH, and biomass. With conventional methods, only a continuously stirred tank reactor configuration gave high aeration rates for cultures in yeast extract peptone dextrose (YPD) medium. For filters technologies, only a polydimethylsiloxan filter provided sufficient aeration of yeast cultures. Further, using the polydimethylsiloxan filter, the YPD medium gave inferior oxygenation rates of yeast compared to superior results with Synthetic Complete medium. It was found that the YPD medium itself, not the yeast cells, interfered with the filter giving the low oxygen transfer rates based on the volumetric transfer coefficient (KLa). The results are discussed for implications of miniaturized bioreactors in low-gravity environments.

A comparative study for production of germ tube in Candida albicans of various pulmonary samples, by different methods in a tertiary care hospital of south west Rajasthan

Background: Systemic candidiasis is associated with a high crude mortality rate, even with first line antifungal therapy. C. albicans is the predominant cause of invasive fungal diseases which is a serious public health issue. The main objective was to assess the reliability of different media for germ tube production in Candida albicans isolated from various clinically diagnosed pulmonary samples.Methods: All Candida isolates were identified and speciated by conventional methods such as Gram’s staining, germ tube test, chlamydospore formation on corn meal agar, sugar fermentation test, sugar assimilation test, and growth on Hi-chrome candida agar.Results: Out of 108 clinical isolates of Candida albicans, 5 different methods were used for germ tube production. Pooled human sera showed 93/108 (86.1%) was the most sensitive method wherein YEPD (yeast extract peptone dextrose) broth 91/108 (84.7%) was the reliable and easy method for detection of germ tube, followed by trypticase soy broth 81/108 (81.4%); peptone water 80/108 (74.7%) and 2% sucrose 71/108 (65.7%).Conclusions: YPED broth is found to be a better serum free substrate and subsequently for the presumptive differentiation of C. albicans from non-albicans candida (NAC), without the extensive time required for the preparation and testing of pooled human serum. Furthermore, this medium is commercially available, more stable, effective, and is not bio hazardous.

Isolation, identification, and characterization of wild budding yeasts from rose flowers in Fukuyama city, Hiroshima, Japan, and their application in bread and wine production.

In this study, we isolated 741 wild budding yeast strains from the flowers of 45 rose cultivars growing in Fukuyama city, Hiroshima, Japan. Of these 741 strains, 21 were found to have high fermentation abilities in yeast extract-peptone-dextrose (YPD) medium. Four of the 21 strains were able to ferment bread dough to make bread. These yeasts were identified as Saccharomyces cerevisiae, Lachancea fermentati, Lachancea kluyveri, and a Torulaspora sp. based on DNA sequences from the 26S rDNA D1/D2 regions. The CO2 production profiles of the bread dough generated by the rose yeasts were evaluated using a Fermograph. Saccharomyces cerevisiae FRY2915 exhibited the highest fermentation capacity. Furthermore, FRY2915 was able to ferment grape juice to produce wine, yielding an alcohol concentration of more than 12%. The four rose yeasts isolated during this study have the potential to produce various types of unique fermented foods, thus enhancing the value of the microbiota associated with rose flowers.

Effect of Different Zinc Sources and Concentrations on the Biomass Yield of Saccharomyces cerevisiae Yeast.

Zinc incorporation and the growth of Saccharomyces cerevisiae were investigated in a culture supplemented with three inorganic zinc salts, i.e. zinc sulphate, zinc chloride and zinc nitrate. The cultivation was performed on a yeast extract peptone dextrose (YEPD) broth medium. The growth of yeast was carried out at different concentrations of zinc, i.e. 0, 30, 60, 90 and 120mg 100ml-1. It was found that the addition of different zinc sources at 30mg 100ml-1 concentration produced higher biomass yield ranging 1.00-1.03g from 100ml-1 of cultivation medium, while higher zinc concentration in the medium caused significantly lower yields of yeast biomass. The amount of zinc in yeast cells was determined by an atomic absorption spectrometer (AAS). The highest amount of zinc in yeast cells was achieved when added in the form of zinc sulphate at a concentration of 120mg 100ml-1. The increment of intracellular zinc was up to 9889.67mgkg-1 of biomass.

Production of Zinc-Yeast from Saccharomyces cerevisiae Fermentation and Determination of Zinc Content by Atomic Absorption Spectrophotometry

Objectives: This study aimed to obtain an optimum method for zincyeast production. Materials and Methods: Production of zinc-yeast was prepared using Yeast Extract Peptone Dextrose (YEPD) as a culture medium. Yeast that had been inoculated into culture media was incubated with a shaker at room temperature for 84 hrs, then zinc sulfate was added with various concentrations of 200, 300, and 400 mg/L, and then incubation continued for 24 hrs. The obtain yeast biomass was dried with a Freeze-dryer and analyzed for total accumulated zinc and protein content. Determination of zinc was using atomic absorption spectrophotometry (AAS) at a wavelength of 196 nm, whereas protein content was determined with Bradford method at a wavelength of 595 nm using UV-Vis spectrophotometer. Results: Zinc-yeast with the addition of 200 mg/L zinc sulfate obtained 0.3111 g that contains 2228.60 μg/g of zinc and 0.8515 mg/L of protein. While zinc-yeast with the addition of 300 mg/L zinc sulfate obtained 0.3704 g that contains 2458.30 μg/g of zinc and 0.8682 mg/L of protein. And the last, zinc-yeast with the addition of 400 mg/L zinc sulfate obtained 0.2370 g that contains 2648.43 μg/g of zinc and 0.8935 mg/L of protein. Conclusion: Production of zinc-yeast with the highest zinc and protein content can be obtained by adding 400 mg/L zinc sulfate solution to the stationary phase culture of S. cerevisiae. The modified zinc-yeast production method is simple and can be used for the production of functional food products.

Metabolic Engineering of Non-carotenoid-Producing Yeast Yarrowia lipolytica for the Biosynthesis of Zeaxanthin.

Zeaxanthin is vital to human health; thus, its production has received much attention, and it is also an essential precursor for the biosynthesis of other critical carotenoids such as astaxanthin and crocetin. Yarrowia lipolytica is one of the most intensively studied non-conventional yeasts and has been genetically engineered as a cell factory to produce carotenoids such as lycopene and β-carotene. However, zeaxanthin production by Y. lipolytica has not been well investigated. To fill this gap, β-carotene biosynthesis pathway has been first constructed in this study by the expression of genes, including crtE, crtB, crtI, and carRP. Three crtZ genes encoding β-carotene hydroxylase from different organisms were individually introduced into β-carotene-producing Y. lipolytica to evaluate their performance for producing zeaxanthin. The expression of crtZ from the bacterium Pantoea ananatis (formerly Erwinia uredovora, Eu-crtZ) resulted in the highest zeaxanthin titer and content on the basis of dry cell weight (DCW). After verifying the function of Eu-crtZ for producing zeaxanthin, the high-copy-number integration into the ribosomal DNA of Y. lipolytica led to a 4.02-fold increase in the titer of zeaxanthin and a 721% increase in the content of zeaxanthin. The highest zeaxanthin titer achieved 21.98 ± 1.80 mg/L by the strain grown on a yeast extract peptone dextrose (YPD)–rich medium. In contrast, the highest content of DCW reached 3.20 ± 0.11 mg/g using a synthetic yeast nitrogen base (YNB) medium to culture the cells. Over 18.0 g/L of citric acid was detected in the supernatant of the YPD medium at the end of cultivation. Furthermore, the zeaxanthin-producing strains still accumulated a large amount of lycopene and β-carotene. The results demonstrated the potential of a cell factory for zeaxanthin biosynthesis and opened up an avenue to engineer this host for the overproduction of carotenoids.

Two-Stage Fermentation of Lipomyces starkeyi for Production of Microbial Lipids and Biodiesel.

The high operating cost is currently a limitation to industrialize microbial lipids production by the yeast Lipomyces starkeyi. To explore economic fermentation technology, the two-stage fermentation of Lipomyces starkeyi using yeast extract peptone dextrose (YPD) medium, orange peel (OP) hydrolysate medium, and their mixed medium were investigated for seven days by monitoring OD600 values, pH values, cell growth status, C/N ratios, total carbon concentration, total nitrogen concentration, residual sugar concentration, lipid content, lipid titer, and fatty acids profiles of lipids. The results showed that two-stage fermentation with YPD and 50% YPD + 50% OP medium contributed to lipid accumulation, leading to larger internal lipid droplets in the yeast cells. However, the cells in pure OP hydrolysate grew abnormally, showing skinny and angular shapes. Compared to the one-stage fermentation, the two-stage fermentation enhanced lipid contents by 18.5%, 27.1%, and 21.4% in the flasks with YPD medium, OP medium, and 50%YPD + 50%OP medium, and enhanced the lipid titer by 77.8%, 13.6%, and 63.0%, respectively. The microbial lipids obtained from both one-stage and two-stage fermentation showed no significant difference in fatty acid compositions, which were mainly dominated by palmitic acid (33.36–38.43%) and oleic acid (46.6–48.12%). Hence, a mixture of commercial medium and lignocellulosic biomass hydrolysate could be a promising option to balance the operating cost and lipid production.