Cryptococcus Curvatus Research Articles

Determination Of Optimal Conditions For Template Sol-Gel Synthesis For The Formation Of Antibacterial Materials

One of the current global problems is the increasing resistance of microorganisms to antibacterial agents and the emergence of associated infections. Therefore, the synthesis of new hybrid materials capable of resisting bacteria is necessary. In this work, loading platforms for antibacterial material based on tetraethoxysilane were formed using yeast cells Ogataea polymorpha BKM Y-2559 and Cryptococcus curvatus VKM Y-3288 as templates under conditions of acid and alkaline hydrolysis. Using scanning electron microscopy, it was shown that an alkaline environment is most optimal when using yeast cells as templates for the formation of a porous material. The surface-active properties of a number of quaternary ammonium compounds were studied using the tensometry method to select the optimal template for the production of antibacterial materials in one stage.

Two-stage process production of microbial lipid by co-fermentation of glucose and N-acetylglucosamine from food wastes with Cryptococcus curvatus

Microbial lipids were produced through a two-stage process with Cryptococcus curvatus by co-fermenting rice and shrimp shells hydrolysates. In the first stage, biomass production of glucose and N-acetylglucosamine was optimized by response surface methodology with the maximum biomass yield (17.60 g/L) under optimum conditions (43.2 g/L mixed sugar concentration, pH 5.8, 200 rpm, and 28 °C). In the second stage, according to a single-factor optimization setting (43.2 g/L sugar mixture solutions, pH 5.5, and shift time of 36 h), lipid titer of 10.08 g/L with content of 55.30 % was achieved. Scaling up to a 5-L bioreactor increased lipid content to 60.07 % with 0.233 g/g yield. When Cryptococcus curvatus was cultured in the blends of rice hydrolysates and shrimp shells hydrolysate, lipid content and yield were 52.25 % and 0.204 g/g. The fatty acid compositions of lipid were similar to those of typical vegetable oils.

Biorefinery of vineyard winter prunings for production of microbial lipids by the oleaginous yeast Cryptococcus curvatus

Spent biomass from agricultural and forestry industries are substantial low-cost carbon source for reducing the input of microbial lipid production. Herein, the components of the vineyard winter prunings (VWPs) from 40 grape cultivars were analyzed. The VWPs contained (w/w) cellulose ranged from 24.8% to 32.4%, hemicellulose 9.6% to 13.8%, lignin 23.7% to 32.4%. The VWPs from Cabernet Sauvignon was processed with the alkali-methanol pretreatment, and 95.8% of the sugars was released from the regenerated VWPs after enzymatic hydrolysis. The hydrolysates from the regenerated VWPs was suitable for lipid production without further treatment as a lipid content of 59% could be achieved with Cryptococcus curvatus. The regenerated VWPs was also used for lipid production via simultaneous saccharification and fermentation (SSF), which led to a lipid yield of 0.088 g/g raw VWPs, 0.126 g/g regenerated VWPs and 0.185 g/g from the reducing sugars. This work demonstrated that the VWPs can be explored for co-production of microbial lipids.

Optimisation of alkaline pretreatment of spent coffee grounds for microbial oil production by Cryptococcus curvatus

In a world of finite resources, the transition to a sustainable post-fossil resources economy is essential. Within this concept, spent coffee grounds (SCGs) could be used for the production of bio-based chemicals, biopolymers and value-added products. Lipids and phenolics were initially extracted from SCGs. Alkaline pretreatment of the remaining SCGs solids has been optimised in this study via Central Composite Design to maximise lignin removal and overall sugar to polysaccharide conversion yield. The optimal SCGs pretreatment conditions were 0.06% (w/v) NaOH and 99.5 °C resulting in 35.7% lignin removal at 60 min pretreatment duration with low glucan and hemicellulose losses (ca. 2.5%). Enzymatic hydrolysis of the remaining SCGs alkaline pretreated solids resulted in 79.4% glucan, 74.5% mannan and 54.8% hemicellulose hydrolysis yield. The SCGs hydrolysate was used as fermentation feedstock in bioreactor cultures of Cryptococcus curvatus resulting in 36.1 g/L microbial oil with 0.25 g/g yield and 0.41 g/(L∙h) productivity. The total dry weight reached 62.7 g/L corresponding to 57.5% (w/w) intracellular lipid content. The microbial oil was rich in oleic acid (55.6%) followed by palmitic acid (18.9%) and stearic acid (14.0%). The proposed process led to the production of 7.81 g microbial oil per 100 g antioxidant- and oil-free SCGs.

Yeast Lipid Produced through Glycerol Conversions and Its Use for Enzymatic Synthesis of Amino Acid-Based Biosurfactants

The aim of the present work was to obtain microbial lipids (single-cell oils and SCOs) from oleaginous yeast cultivated on biodiesel-derived glycerol and subsequently proceed to the enzymatic synthesis of high-value biosurfactant-type molecules in an aqueous medium, with SCOs implicated as acyl donors (ADs). Indeed, the initial screening of five non-conventional oleaginous yeasts revealed that the most important lipid producer was the microorganism Cryptococcus curvatus ATCC 20509. SCO production was optimised according to the nature of the nitrogen source and the initial concentration of glycerol (Glyc0) employed in the medium. Lipids up to 50% w/w in dry cell weight (DCW) (SCOmax = 6.1 g/L) occurred at Glyc0 ≈ 70 g/L (C/N ≈ 80 moles/moles). Thereafter, lipids were recovered and were subsequently used as ADs in the N-acylation reaction catalysed by aminoacylases produced from Streptomyces ambofaciens ATCC 23877 under aqueous conditions, while Candida antarctica lipase B (CALB) was used as a reference enzyme. Aminoacylases revealed excellent activity towards the synthesis of acyl-lysine only when free fatty acids (FAs) were used as the AD, and the rare regioselectivity in the α-amino group, which has a great impact on the preservation of the functional side chains of any amino acids or peptides. Aminoacylases presented higher α-oleoyl-lysine productivity and final titer (8.3 g/L) with hydrolysed SCO than with hydrolysed vegetable oil. The substrate specificity of both enzymes towards the three main FAs found in SCO was studied, and a new parameter was defined, viz., Specificity factor (Sf), which expresses the relative substrate specificity of an enzyme towards a FA present in a FA mixture. The Sf value of aminoacylases was the highest with palmitic acid in all cases tested, ranging from 2.0 to 3.0, while that of CALB was with linoleic acid (0.9-1.5). To the best of our knowledge, this is the first time that a microbial oil has been successfully used as AD for biosurfactant synthesis. This bio-refinery approach illustrates the concept of a state-of-the-art combination of enzyme and microbial technology to produce high-value biosurfactants through environmentally friendly and economically sound processes.

Growth Potential of Selected Yeast Strains Cultivated on Xylose-Based Media Mimicking Lignocellulosic Wastewater Streams: High Production of Microbial Lipids by Rhodosporidium toruloides

The potential of Rhodosporidium toruloides, Candida oleophila, Metschnikowia pulcherima, and Cryptococcus curvatus species to produce single-cell-oil (SCO) and other valuable metabolites on low-cost media, based on commercial-type xylose, was investigated. Rhodosporidium strains were further evaluated in shake-flasks using different lignosulphonate (LS) concentrations, in media mimicking waste streams derived from the paper and pulp industry. Increasing the LS concentration up to 40 g/L resulted in enhanced dry cell weight (DCW) while SCO production increased up to ~5.0 g/L when R. toruloides NRRL Y-27012 and DSM 4444 were employed. The intra-cellular polysaccharide production ranged from 0.9 to 2.3 g/L in all fermentations. Subsequent fed-batch bioreactor experiments with R. toruloides NRRL Y-27012 using 20 g/L of LS and xylose, led to SCO production of 17.0 g/L with maximum lipids in DCW (YL/X) = 57.0% w/w. The fatty acid (FA) profile in cellular lipids showed that oleic (50.3–63.4% w/w) and palmitic acid (23.9–31.0%) were the major FAs. Only SCO from batch trials of R. toruloides strains contained α-linolenic acid. Media that was supplemented with various LS concentrations enhanced the unsaturation profile of SCO from R. toruloides NRRL Y-27012. SCO from R. toruloides strains could replace plant-based commodity oils in oleochemical-operations and/or it could be micro- and nano-encapsulated into novel food-based formulas offering healthier food-products.

Biotechnological Conversions of Mizithra Second Cheese Whey by Wild-Type Non-Conventional Yeast Strains: Production of Yeast Cell Biomass, Single-Cell Oil and Polysaccharides

The cultivation of oleaginous yeasts on various agro-industrial residues and the subsequent production of microbial lipids (single-cell oils), which can be used as starting materials for the synthesis of both “second generation” biodiesel and various types of oleochemicals, is considered as one of the most important approaches of the Industrial Biotechnology, in terms of circular economy and green and sustainable development. In this study, seven wild-type non-conventional yeast strains were evaluated for their growth on a semi-defined medium with cheese whey lactose as a sole carbon source. Five of these strains were further batch-cultivated into the complex substrate that contained second cheese whey, which is the main by-product of Mizithra whey cheese manufacture, after centrifugation and filtration without any extra mineral salts, carbon, or nitrogen source addition. All these five strains grown in second cheese whey produced mainly yeast biomass and to lesser extent microbial lipids and other interesting metabolites, such as polysaccharides. The strain Cryptococcus curvatus ATCC 20509 produced the highest total dry weight (TDW) amount (22.4 g/L), that contained 3.4 g/L of intra-cellular lipids, followed by C. curvatus NRRL Y-1511, which produced 20.6 g/L of TDW and 3.2 g/L lipids. A novel, non-previously systematically studied strain, namely Papiliotrema laurentii NRRL Y-2536, produced significant quantities of TDW (22.0 g/L) and, interestingly, secreted quantities of exopolysaccharides. Fed-batch shake-flask cultivation of C. curvatus ATCC 20509 in pretreated second cheese whey, pulse-supplemented with condensed cheese whey-derived lactose, led to the significant TDW quantity of 38.1 g/L that contained c. 57% w/w of total lipids (lipids at a concentration 21.7 g/L were produced). Cellular lipids of all microorganisms, mainly stored as triacylglycerols, contained in variable quantities the fatty acids Δ9C18:1, C16:0, Δ9,12C18:2 and C18:0, constituting perfect candidates for the synthesis of “second generation” biodiesel.

Evaluation and Identification of Key Economic Bottlenecks for Cost-Effective Microbial Oil Production from Fruit and Vegetable Residues

Intensive horticultural systems for the production of vegetables in greenhouses represent one of the main industries generating organic waste, as those that do not meet the quality standards for the fresh market or the processing industry are discarded. This highlights the importance of using these residues as raw material for other applications, such as bioenergy and bioproducts production, within the framework of a bio-based economy that maximizes the utilization of biomass resources in a sustainable manner. In this work, the microbial oil production from discarded pepper using the oleaginous yeast Cryptococcus curvatus was evaluated. Overall, a total lipid accumulation of 16.8 g/L was achieved with a fatty acid profile suitable to produce biodiesel. The lipid yield obtained was 0.12 g/g sugars. In addition, experimental results were used to assess the techno-economic feasibility of a proposed microbial oil plant using the software Aspen Plus. This plant yields approximately 96 kg of microbial oils/ton dry discarded pepper, with an estimated Minimum Selling Price of 7 €·kg−1. These figures point out the necessity of increasing the yield of microbial oil production and considering the utilization of possible by-products, such as mannitol and cell debris, to improve the economic performance of the process.

Investigating the Bioconversion Potential of Volatile Fatty Acids: Use of Oleaginous Yeasts Rhodosporidium toruloides and Cryptococcus curvatus towards the Sustainable Production of Biodiesel and Odd-Chain Fatty Acids

Oleaginous yeasts have attracted increasing scientific interest as single cell oil (SCO) producers. SCO can be used as a fossil-free fuel substitute, but also as a source of rarely found odd-chain fatty acids (OCFAs), such as C15, C17, and C25 fatty acids which have a wide range of nutritional and biological applications. Volatile fatty acids (VFAs) have gained interest as sustainable carbon source for yeasts. This study aims to improve current knowledge on yeast species that yield high amounts of SCO using VFAs as a carbon source. Specifically, the growth of the promising yeasts Cryptococcus curvatus and Rhodotorula toruloides was evaluated on individual VFAs, such as acetic, propionic, and butyric acid. C. curvatus proved to be more tolerant in higher concentrations of VFAs (up to 60 g/L), while butyric acid favored biomass and lipid conversion (0.65 and 0.23 g/gsubstrate, respectively). For R. toruloides, butyric acid favored biomass conversion (0.48 g/gsubstrate), but lipid conversion was favored using acetic acid, instead (0.14 g/gsubstrate). Propionic acid induced the formation of OCFAs, which yielded higher amounts for C. curvatus (up to 2.17 g/L). VFAs derived from the anaerobic digestion of brewer’s spent grain were tested as a cost-competitive carbon source and illustrated the significance of the combination of different VFAs in the quality of the produced SCO, by improving the biodiesel properties and OCFAs production.

Clinical epidemiology and high genetic diversity amongst Cryptococcus spp. isolates infecting people living with HIV in Kinshasa, Democratic Republic of Congo.

Neuromeningeal cryptococcosis (NMC) is a life-threatening opportunistic infection in advanced HIV disease patients (AHDP). It is caused by Cryptococcus spp. complexes and mainly occurs in sub-Saharan Africa. In this study, we performed molecular characterization and antifungal susceptibility profiling of Cryptococcus isolates from AHDP in Kinshasa (DRC). Additionally, we investigated a possible association between NMC severity factors and the Cryptococcus neoformans (Cn) multilocus sequence typing (MLST) profiles. We characterized the isolates using PCR serotyping, MALDI-TOF MS, internal transcribed spacer (ITS) sequencing, and MLST. Susceptibility testing for the major antifungal drugs was performed according to the EUCAST guidelines. Parameters associated with NMC severity, such as hypoglycorrhachia (< 50 mg/dL), increased cerebral spinal fluid opening pressure (> 30 cm H2O), and poor therapeutic outcome were compared with the Cn MLST sequences type (ST). Twenty-three out of 29 Cryptococcus isolates were identified as serotype A using PCR serotyping (79.3%; 95% IC: 65.5-93.1), while six (20.7%; 95% IC: 6.9-34.5) were not serotypable. The 29 isolates were identified by ITS sequencing as follows: Cryptococcus neoformans (23/29, 79.3%), Cutaneotrichosporon curvatus (previously called Cryptococcus curvatus) (5/29, 17.2%), and Papiliotrema laurentii (Cryptococcus laurentii) (1/29, 3.5%). Using the ISHAM MLST scheme, all Cn isolates were identified as molecular type VNI. These comprised seven different STs: ST93 (n = 15), ST5 (n = 2), ST53 (n = 1), ST31 (n = 1), ST4 (n = 1), ST69 (n = 1), and one novel ST that has not yet been reported from other parts of the world and was subsequently assigned as ST659 (n = 2). Of the included strains, only Papiliotrema laurentii was resistant to amphoterin B (1/29, 3.5%), 6.8% (2/29) were resistant to 5-flucytosine (the single Papiliotrema laurentii strain and one Cryptococcus neoformans isolate), and 13.8% (4/29) to fluconazole, including two of five (40%) Cutaneotrichosporon curvatus and two of 23 (8.7%) C. neoformans strains. We found a significative association between poor therapeutic outcome and a non-ST93 sequence type of causative strains (these concerned the less common sequence types: ST53, ST31, ST5, ST4, ST659, and ST69) (87.5% versus 40%, p = 0.02). Molecular analysis of Cryptococcus spp. isolates showed a wide species diversity and genetic heterogenicity of Cn within the VNI molecular type. Furthermore, it is worrying that among included strains we found resistances to several of the commonly used antifungals.

Sensitivity Profile of Fungal Pathogens Responsible for Lower Respiratory Tract Infections in Yaounde

Background: Infectious diseases of the respiratory tract are known as respiratory tract infections (RTIs). An infection of this type usually is further classified as an upper respiratory tract infection (URI or URTI) or a lower respiratory tract infection (LRI or LRTI). LRIs are the leading cause of death among all infectious diseases. The objective of our study was to bring out the sensitivity profile of fungal pathogens responsible for lower respiratory tract infections in Yaounde Methods: We carried out a transverse and descriptive study during a 6 month period (February to June 2021), at the Jamot hospital in Yaounde. Included in this study were patients suffering from a lower respiratory tract infection from whom the medical practitioner had requested a sputum or broncho alveolar liquid analysis A macroscopic, microscopic, fungal culture of the sample was carried out and a germ tube test, fungal sensitivity test as well as specie identification using the ID 32 C gallery was carried out on the positive cultures Statistical analysis was carried out using the R version 3.6.1 software. The mean was calculated with the aid of the Kruskal Wallis rank sum test. Results: 300 patients participated in this study. They had mean age ± standard deviation of 41.59 ± 17.5 years and extremities of 1 and 91years. The male /female ratio was 2:1 Fungal infection was positive in 127 patients (42.33 %), 75 (59%) Candida albicans, 25 (19.68%) Cryptococcus humicola, 10 (7.87%) Candida tropicalis, 6 (4.72%) Candida krusei, 4 (3.14%) Candida famata, 4 (3.14%) Candida sake and 3 (2.36%) Cryptococcus curvatus. As far as antifungigram is concerned, the total drug susceptibility was Nystatine (98.47%), Amphotericine B (86.91%), Miconazole (55.42%), Econazole (52.61%), Ketoconazole (52.57%) and Fluconazole (14.42%).The prevalence of fungal pathogens was 42.33%. Of the 300 patients, 71 had tuberculosis, 24 were HIV positive and 6 were diabetic we had 5 patients with HIV, tuberculosis and fungal co-infection, 16 with HIV and fungal co-infection and 6 with HIV and tuberculosis co-infection. Conclusion: This study shows a relative high prevalence (42.33%) of the colonization of the respiratory tract by fungal pathogens. The fungal pathogens responsible for lower respiratory tract infections are Candida albicans, Candida tropicalis, Candida krusei, Candida famata, Candida sake, Cryptococcus humicola and Cryptococcus curvatus. The drug of choice is Nystatine and Fluconazole presents a very limited activity. Additional studies should be carried out in other towns in order to better document this issue in Cameroon.

Single-Cell Oils from Oleaginous Microorganisms as Green Bio-Lubricants: Studies on Their Tribological Performance

Biolubricants refer to eco-friendly, biodegradable, and non-toxic lubricants. Their applications are still limited compared to mineral oils; however, their sustainable credentials are making them increasingly attractive. Vegetable oils are frequently used for this purpose. However, vegetable oils have issues of low lipid productivity, dependence on climatic conditions, and need for agricultural land. Microbial oils represent a more sustainable alternative. To ensure their widespread applicability, the suitability of microbial oils from a physicochemical point of view needs to be determined first. In this study, oils obtained from various oleagenic microbes—such as microalgae, thraustochytrids, and yeasts—were characterized in terms of their fatty acid profile, viscosity, friction coefficient, wear, and thermal stability. Oleaginous microalgal strains (Auxenochlorella protothecoides and Chlorella sorokiniana), thraustochytrids strains (Aurantiochytrium limacinum SR21 and Aurantiochytrium sp. T66), and yeast strains (Rhodosporidium toruloides and Cryptococcus curvatus) synthesized 64.5%, 35.15%, 47.89%, 47.93%, 56.42%, and 52.66% of lipid content, respectively. Oils from oleaginous microalgae (A. protothecoides and C. sorokiniana) and yeasts (R. toruloides and C. curvatus) possess excellent physicochemical and tribological qualities due to high amount of monounsaturated fatty acids (oleic acid C18:1 content, 56.38%, 58.82%, 46.67%, 38.81%) than those from oleaginous thraustochytrids (A. limacinum SR21 and Aurantiochytrium sp. T66; 0.96%, 0.08%, respectively) supporting their use as renewable and biodegradable alternatives to traditional mineral oil-based lubricants. Oil obtained from microalgae showed a lower friction coefficient than oils obtained from yeasts and thraustochytrids.

OENOLOGICAL CHARACTERISTICS AND VINIFICATION RESULTS OF THE YEAST OF MALAGOUSIA GRAPE ISOLATED IN GREECE

Malagousia grapes, selected from 5 different PGI Greek zones, in 3 different growing seasons (2018-2019, 2019-2020, 2020-2021) were collected in the stage of technological maturity. Quantity of 25 Kg grapes fermented spontaneously in 30 l thermo regulated stain steel tanks, produced white wine. The indigenous yeast flora, isolated at three phases of the alcoholic fermentations, was studied. Different yeast species were isolated, purified and characterized. The restriction fragment length polymorphism of PCR-amplified fragments from the rDNA gene cluster (PCR RFLP of rDNA) has been used for the differentiation of yeast species. The standard identification procedure has been performed on representative strains that shared identical RFLP profiles showed great diversity of the yeast population. Including grape berries, must and fermented must, the following yeast species were identified: a number of Pichia and Candida species, Kloeckera apiculata, Cryptococcus curvatus, Metschnikowia pulcherrima, Kluyveromyces, as well as Saccharomyces cerevisiae and Saccharomyces stranieri. We performed microscopic, macroscopic and carbon assimilation tests by API 32C standardized system, biotechnological testing and hydrolase profiling obtained by the API-ZYM system. The most significant findings in population dynamics of yeasts in the spontaneous fermentations were bigger diversity of different species of Non- Saccharomyces in organic grapes and almost complete absence of non-Saccharomyces species, at least at grapes and at the beginning of the alcoholic fermentations at conventionally cultivated grapes, from all the examined PGI zones in all the three years of the study. The use and enhancement of indigenous yeasts is an increasing trend. Rapid identification of the yeast population is necessary for successful monitoring of the fermentation process and for obtaining a good wine quality as well as contributing to the optimization of Greek wine production.

Volatile Fatty Acids from Lipid-Extracted Yeast Provide Additional Feedstock for Microbial Lipid Production

Microbial lipid production from oleaginous yeasts is a promising process for the sustainable development of the microbial biodiesel industry. However, the feedstock cost poses an economic problem for the production of microbial biodiesel. After lipid extraction, yeast biomass can be used as an organic source for microbial biodiesel production. In this study, volatile fatty acids (VFAs), produced via anaerobic digestion of a lipid-extracted yeast (LEY) residue, were utilized as a carbon source for the yeast Cryptococcus curvatus. The response surface methodology was used to determine the initial pH and inoculum volume for the optimal VFA production. The experimental result for VFA concentration was 4.51 g/L at an initial pH of 9 and an inoculation 25%. The optimization results from the response surface methodology showed that the maximal VFA concentration was 4.58 g/L at an initial pH of 8.40 and an inoculation of 39.49%. This study indicates that VFAs from LEY can be used as a carbon source for microbial biodiesel production, with the potential to significantly reduce feedstock costs.

Conversion of Arthrospira platensis Biomass into Microbial Lipids by the Oleaginous Yeast Cryptococcus curvatus

Conversion of <i>Arthrospira platensis</i> Biomass into Microbial Lipids by the Oleaginous Yeast <i>Cryptococcus curvatus</i>

Co‐utilization of amino acid‐rich wastes and glycerol for microbial lipid production

AbstractMicrobial lipids are considered to be potential raw materials for biodiesel production. However, the costs of such a process remain high due to the use of expensive feedstocks for microbial lipid production. The meat industry and biodiesel refineries generate amino acid (AA) wastes and crude glycerol, respectively, which could be explored as relatively cheap feedstocks for oleaginous yeasts. Unfortunately, AA wastes have a high nitrogen content and crude glycerol contains several impurities, discouraging microbial lipid production. Here, glycerol was co‐used with AA, or with AA blends with compositional profiles matching those of different meats, so that the media had favorable carbon‐to‐nitrogen (C/N) ratios to promote AA conversion into lipids using the oleaginous yeast Cryptococcus curvatus ATCC 20509 under two‐stage culture conditions. Co‐utilization of glycerol and AA resulted in improved lipid production. The highest lipid yield of 20.9 g 100 g–1 was achieved with lysine and glycerol, where the lipid yield was 13.9 g 100 g–1, using an AA blend of similar composition to sheep viscera and glycerol. The lipid products comprised over 93% of 16 and 18 carbon‐containing fatty acids, showing high potential for biodiesel production. The co‐use of glycerol with AA improved AA conversion into lipids while decreasing the inhibitory effects at relatively high AA concentrations. The utilization of crude glycerol and AA‐rich wastes from the meat industry could help both the development of biorefineries and waste minimization. © 2021 Society of Chemical Industry and John Wiley &amp; Sons, Ltd

Yeast fermentation towards biodiesel: Maximizing resource recovery by integrating with biohydrogen production in biorefinery framework

This study presents an effective and sustainable approach for biodiesel production through oleaginous yeast fermentation by utilizing volatile fatty acids (VFAs) rich acidogenic effluents as an alternative feedstock. Experiments were designed in two stages to obtain high cell density and lipid productivity. Primarily, oleaginous yeast (Cryptococcus curvatus; MTCC 2698) was grown on glucose with varied initial concentrations at 25 °C. Maximum biomass concentration of 4.2 ± 0.05 g/L was achieved with 40 g/L glucose, which was subjected to the second stage along with the supplementation of 5 g/L of selected VFAs viz., acetic acid, propionic acid, butyric acid and mixed VFAs. Highest lipid concentration of 33.5% (w/w) was obtained with acetic acid supplementation followed by mixed VFAs (23% w/w). Further, to validate results from initial studies, yeast strain was cultivated on real field VFAs rich acidogenic effluent derived from renewable biohydrogen production process. Maximum of 4.85 ± 0.05 g/L biomass and 29.3% (w/w) of lipid was observed during real field application fatty acid profiling of produced lipids showed predominance of palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1) and linoleic acid (C18:2) which has potential utility for biodiesel production. Integration of bioprocesses in a biorefinery format helps to maximize resource recovery apart from minimizing waste generation. The study confirms feasible utilization of acidogenic effluent as an alternative feedstock for the production of microbial lipids through yeast fermentation.

Lipid Production by Yeasts Growing on Commercial Xylose in Submerged Cultures with Process Water Being Partially Replaced by Olive Mill Wastewaters

Six yeast strains belonging to Rhodosporidium toruloides, Lipomyces starkeyi, Rhodotorula glutinis and Cryptococcus curvatus were shake-flask cultured on xylose (initial sugar—S0 = 70 ± 10 g/L) under nitrogen-limited conditions. C. curvatus ATCC 20509 and L. starkeyi DSM 70296 were further cultured in media where process waters were partially replaced by the phenol-containing olive mill wastewaters (OMWs). In flasks with S0 ≈ 100 g/L and OMWs added yielding to initial phenolic compounds concentration (PCC0) between 0.0 g/L (blank experiment) and 2.0 g/L, C. curvatus presented maximum total dry cell weight—TDCWmax ≈ 27 g/L, in all cases. The more the PCC0 increased, the fewer lipids were produced. In OMW-enriched media with PCC0 ≈ 1.2 g/L, TDCW = 20.9 g/L containing ≈ 40% w/w of lipids was recorded. In L. starkeyi cultures, when PCC0 ≈ 2.0 g/L, TDCW ≈ 25 g/L was synthesized, whereas lipids in TDCW = 24–28% w/w, similar to the experiments without OMWs, were recorded. Non-negligible dephenolization and species-dependent decolorization of the wastewater occurred. A batch-bioreactor trial by C. curvatus only with xylose (S0 ≈ 110 g/L) was performed and TDCW = 35.1 g/L (lipids in TDCW = 44.3% w/w) was produced. Yeast total lipids were composed of oleic and palmitic and to lesser extent linoleic and stearic acids. C. curvatus lipids were mainly composed of nonpolar fractions (i.e., triacylglycerols).

Lipid production by Cryptococcus curvatus growing on commercial xylose and subsequent valorization of fermentation waste-waters for the production of edible and medicinal mushrooms

A rarely studied Cryptoccus curvatus strain (viz. NRRL Y-1511) was cultivated in shake-flask submerged nitrogen-limited experiments, with commercial xylose being employed as substrate and has been proved as quite appropriate for total biomass, lipid and endopolysaccharide production. A batch bioreactor trial compared to the equivalent shake-flask experiment showed larger amounts of total lipid and biomass produced. Total dry biomass of 26.1 g/L containing c. 30 % of lipids was synthesized. Endopolysaccharides in relatively high concentrations were synthesized in the early growth stages decreasing afterwards in favor of storage lipid synthesis. Lipid production bioprocess was successfully simulated by a modified Velruyten-Aggelis model and the optimized parameter values were found to be similar to those experimentally measured. Lipids contained mostly neutral fractions (triacylglycerols) and were rich in the fatty acid Δ9C18:1, constituting a suitable starting material for the synthesis of high-quality biodiesel. Within the frame of bio-refinery, lipid fermentation waste-waters were used as maceration waters for a novel mushroom cultivation process of Pleurotus ostreatus, Lentinula edodes and Ganoderma adspersum edible and medicinal mushrooms. These waste-waters were used for first time in mushroom cultivation process demonstrating positive effect on laccase and sporophore production by these mushroom species.

Microbial lipid production from rice straw hydrolysates and recycled pretreated glycerol

Microbial lipids were produced by both rice straw hydrolysates and recycled pretreated glycerol. First, lipid fermentation of glucose via Cryptococcus curvatus was optimized by response surface methodology. Variables were selected by Plackett–Burman design, and optimized by central composite design, achieving 4.9 g/L total lipid and 0.16 g/g lipid yield, and increased further as glucose increased from 30 to 50 g/L. Secondly, after pretreatment, 72% lignin of rice straw was removed with glucose yield increased by 2.4 times to 74% at 20% substrate and 3 FPU/g. Subsequently, its hydrolysates produced high total lipid (8.8 g/L) and lipid yield (0.17 g/g). Finally, recycled glycerol reached the maximum total lipid of 7.2 g/L and high lipid yield of 0.16 g/g. Based on the calculation, 2.9 g total lipid would be produced from 1 g rice straw and the recycled glycerol, with a similar composition to soybean oil.