Inulinase production by a marine yeast Pichia guilliermondii and inulin hydrolysis by the crude inulinase

Selection of Potential Yeast Probiotics and a Cell Factory for Xylitol or Acid Production from Honeybee Samples

Excessive use of antibiotics has detrimental consequences, including antibiotic resistance and gut microbiome destruction. Probiotic-rich diets help to restore good microbes, keeping the body healthy and preventing the onset of chronic diseases. Honey contains not only prebiotic oligosaccharides but, like yogurt and fermented foods, is an innovative natural source for probiotic discovery. Here, a collection of three honeybee samples was screened for yeast strains, aiming to characterize their potential in vitro probiotic properties and the ability to produce valuable metabolites. Ninety-four isolates out of one-hundred and four were able to grow at temperatures of 30 °C and 37 °C, while twelve isolates could grow at 42 °C. Fifty-eight and four isolates displayed the ability to grow under stimulated gastrointestinal condition, at pH 2.0-2.5, 0.3% (w/v) bile salt, and 37 °C. Twenty-four isolates showed high autoaggregation of 80-100% and could utilize various sugars, including galactose and xylose. The cell count of these isolates (7-9 log cfu/mL) was recorded and stable during 6 months of storage. Genomic characterization based on the internal transcribed spacer region (ITS) also identified four isolates of Saccharomyces cerevisiae displayed good ability to produce antimicrobial acids. These results provided the basis for selecting four natural yeast isolates as starter cultures for potential probiotic application in functional foods and animal feed. Additionally, these S. cerevisiae isolates also produced high levels of acids from fermented sugarcane molasses, an abundant agricultural waste product from the sugar industry. Furthermore, one of ten identified isolates of Meyerozyma guilliermondiii displayed an excellent ability to produce a pentose sugar xylitol at a yield of 0.490 g/g of consumed xylose. Potentially, yeast isolates of honeybee samples may offer various biotechnological advantages as probiotics or metabolite producers of multiproduct-based lignocellulosic biorefinery.

Coupling azo dye degradation and biodiesel production by manganese-dependent peroxidase producing oleaginous yeasts isolated from wood-feeding termite gut symbionts

BACKGROUND

Textile industry represents one prevalent activity worldwide, generating large amounts of highly contaminated and rich in azo dyes wastewater, with severe effects on natural ecosystems and public health. However, an effective and environmentally friendly treatment method has not yet been implemented, while concurrently, the increasing demand of modern societies for adequate and sustainable energy supply still remains a global challenge. Under this scope, the purpose of the present study was to isolate promising species of yeasts inhabiting wood-feeding termite guts, for combined azo dyes and textile wastewater bioremediation, along with biodiesel production.

RESULTS

Thirty-eight yeast strains were isolated, molecularly identified and subsequently tested for desired enzymatic activity, lipid accumulation, and tolerance to lignin-derived metabolites. The most promising species were then used for construction of a novel yeast consortium, which was further evaluated for azo dyes degradation, under various culture conditions, dye levels, as well as upon the addition of heavy metals, different carbon and nitrogen sources, and lastly agro-waste as an inexpensive and environmentally friendly substrate alternative. The novel yeast consortium, NYC-1, which was constructed included the manganese-dependent peroxidase producing oleaginous strains Meyerozyma caribbica, Meyerozyma guilliermondii, Debaryomyces hansenii, and Vanrija humicola, and showed efficient azo dyes decolorization, which was further enhanced depending on the incubation conditions. Furthermore, enzymatic activity, fatty acid profile and biodiesel properties were thoroughly investigated. Lastly, a dye degradation pathway coupled to biodiesel production was proposed, including the formation of phenol-based products, instead of toxic aromatic amines.

CONCLUSION

In total, this study might be the first to explore the application of MnP and lipid-accumulating yeasts for coupling dye degradation and biodiesel production.

Biotechnological applications of the non-conventional yeast Meyerozyma guilliermondii

Unconventional yeasts have attracted increased attentions owning to their unique biochemical properties and potential application in the biotechnological process. With the rapid development of microbial isolation tools and synthetic biology, more promising industrial yeasts have been isolated and characterized. Meyerozyma guilliermondii (anamorph Candida guilliermondii) is an ascomycetous yeast with several unique characteristics and physiology, such as the wide substrates spectrum and capability of various chemicals synthesis. The potential physiological and metabolic capabilities of M. guilliermondii, which can utilize various carbon sources including typical hydrophilic and hydrophobic materials were first reviewed in this review. Moreover, the wide applications of M. guilliermondii, such as for industrial enzymes production, metabolites synthesis and biocontrol were also reviewed. With the development of system and synthetic biology, M. guilliermondii will provide new opportunities for potential applications in biotechnology sectors in the future.

Engineering Yarrowia lipolytica for the Synthesis of Glutathione from Organic By-Products

Tripeptide glutathione, which plays important roles in many cellular mechanisms, is also a biotechnology-oriented molecule with applications in medicine, food and cosmetic. Here, the engineering of the yeast Yarrowia lipolytica for the production of this metabolite at high titer values from various agro-industrial by-products is reported. The constitutive overexpression of the glutathione biosynthetic genes GSH1 and GSH2 encoding respectively γ-glutamylcysteine synthetase and glutathione synthetase, together with the INU1 gene from Kluyveromyces marxianus encoding inulinase yielded a glutathione titer value and a productivity of 644 nmol/mg protein and 510 µmol/g_DCW, respectively. These values were obtained during bioreactor batch cultures in a medium exclusively comprising an extract of Jerusalem artichoke tuber, used as a source of inulin, and ammonium sulfate, used as a nitrogen source.

Purification and molecular characterization of a Metschnikowia saccharicola killer toxin lethal to a crab pathogenic yeast

The marine yeast strain Metschnikowia saccharicola DD21-2, isolated from sediments in the Yalu River, produces a killer toxin with a lethal effect on Metschnikowia bicuspidate strain WCY, a pathogenic yeast strain that infects crabs. In this study, the killer toxin was purified and characterized. After sequential purification, the purity of the killer toxin was increased 72.2-fold over the purity of the yeast cell culture supernatant. The molecular weight of the purified killer toxin was 47.0 kDa. The optimal pH and temperature for killing activity were 5.5°C and 16°C, respectively. The killing activity was stable over a pH range of 4.0-6.5 and temperature range of 0°C-40°C. The purified killer toxin was only effective against toxin-sensitive integral cells and had no killing effect on the protoplasts of toxin-sensitive cells. When exerting the killing effect, the toxin bind to a cell wall receptor of the treated strain, disrupted cell wall integrity and eventually caused death. The amino acid sequence identified by mass spectroscopy indicated that the purified killer toxin might be a protein kinase, but did not show β-1,3-glucanase activity, consistent with the laminarin hydrolysis results. These findings provide a basis for disease prevention and control in marine aquaculture.

Evaluation of carbon sources for the production of inulinase by Aspergillus niger A42 and its characterization

Inulinases are used for the production of high-fructose syrup and fructooligosaccharides, and are widely utilized in food and pharmaceutical industries. In this study, different carbon sources were screened for inulinase production by Aspergillus niger in shake flask fermentation. Optimum working conditions of the enzyme were determined. Additionally, some properties of produced enzyme were determined [activation (E_a)/inactivation (E_ia) energies, Q₁₀ value, inactivation rate constant (k_d), half-life (t_1/2), D value, Z value, enthalpy (ΔH), free energy (ΔG), and entropy (ΔS)]. Results showed that sugar beet molasses (SBM) was the best in the production of inulinase, which gave 383.73 U/mL activity at 30 °C, 200 rpm and initial pH 5.0 for 10 days with 2% (v/v) of the prepared spore solution. Optimum working conditions were 4.8 pH, 60 °C, and 10 min, which yielded 604.23 U/mL, 1.09 inulinase/sucrase ratio, and 2924.39 U/mg. Additionally, E_a and E_ia of inulinase reaction were 37.30 and 112.86 kJ/mol, respectively. Beyond 60 °C, Q₁₀ values of inulinase dropped below one. At 70 and 80 °C, t_1/2 of inulinase was 33.6 and 7.2 min; therefore, inulinase is unstable at high temperatures, respectively. Additionally, t_1/2, D, ΔH, ΔG values of inulinase decreased with the increase in temperature. Z values of inulinase were 7.21 °C. Negative values of ΔS showed that enzymes underwent a significant process of aggregation during denaturation. Consequently, SBM is a promising carbon source for inulinase production by A. niger. Also, this is the first report on the determination of some properties of A. niger A42 (ATCC 204,447) inulinase.

Organic Wastes as Feedstocks for Non-Conventional Yeast-Based Bioprocesses

Non-conventional yeasts are efficient cell factories for the synthesis of value-added compounds such as recombinant proteins, intracellular metabolites, and/or metabolic by-products. Most bioprocess, however, are still designed to use pure, ideal sugars, especially glucose. In the quest for the development of more sustainable processes amid concerns over the future availability of resources for the ever-growing global population, the utilization of organic wastes or industrial by-products as feedstocks to support cell growth is a crucial approach. Indeed, vast amounts of industrial and commercial waste simultaneously represent an environmental burden and an important reservoir for recyclable or reusable material. These alternative feedstocks can provide microbial cell factories with the required metabolic building blocks and energy to synthesize value-added compounds, further representing a potential means of reduction of process costs as well. This review highlights recent strategies in this regard, encompassing knowledge on catabolic pathways and metabolic engineering solutions developed to endow cells with the required metabolic capabilities, and the connection of these to the synthesis of value-added compounds. This review focuses primarily, but not exclusively, on Yarrowia lipolytica as a yeast cell factory, owing to its broad range of naturally metabolizable carbon sources, together with its popularity as a non-conventional yeast.

Production of high titer of citric acid from inulin

BACKGROUND

Citric acid is considered as the most economically feasible product of microbiological production, therefore studies on cheap and renewable raw materials for its production are highly desirable. In this study citric acid was synthesized by genetically engineered strains of Yarrowia lipolytica from widely available, renewable polysaccharide - inulin. Hydrolysis of inulin by the Y. lipolytica strains was established by expressing the inulinase gene (INU1 gene; GenBank: X57202.1) with its native secretion signal sequence was amplified from genomic DNA from Kluyveromyces marxianus CBS6432. To ensure the maximum citric acid titer, the optimal cultivation strategy-repeated-batch culture was applied.

RESULTS

The strain Y. lipolytica AWG7 INU 8 secreted more than 200 g dm- 3 of citric acid during repeated-batch culture on inulin, with a productivity of 0.51 g dm- 3 h- 1 and a yield of 0.85 g g- 1.

CONCLUSIONS

The citric acid titer obtained in the proposed process is the highest value reported in the literature for Yarrowia yeast. The obtained results suggest that citric acid production from inulin by engineered Y. lipolytica may be a very promising technology for industrial citric acid production.

Systematic unravelling of the inulin hydrolase from Bacillus amyloliquefaciens for efficient conversion of inulin to poly-(γ-glutamic acid)

BACKGROUND

Bacillus amyloliquefaciens NB is a newly discovered strain, which produces poly-(γ-glutamic acid) (γ-PGA) from raw extracted inulin of Jerusalem artichoke tubers; however, the underlying mechanisms remain unknown. To address this problem, we identified the inulin hydrolase in wild-type strain B. amyloliquefaciens NB.

RESULTS

The novel inulin hydrolase (CscA) was discovered from strain NB, with high inulinase activity (987.0 U/mg at 55 °C) and strong resistance at pH values between 8.0 and 11.0, suggesting the potential application of CscA in Jerusalem artichoke biorefinery. CscA exhibited a k _cat/K _m of (6.93 ± 0.27) × 10³ for inulin; its enzymatic activity was stimulated by metal ions, like K⁺, Mn²⁺, or Ca²⁺. Similar to their role in glycoside hydrolase 32 family enzymes, the conserved Asp37, Asp161, and Glu215 residues of CscA contribute to its catalytic activity. Targeted disruption of CscA gene suppressed inulin utilization by strain NB. Overexpression of CscA significantly enhanced the γ-PGA generation by 19.2% through enhancement in inulin consumption.

CONCLUSIONS

The inulin hydrolase CscA is critical for inulin metabolism in B. amyloliquefaciens and indicates potential application in Jerusalem artichoke biorefinery.

Recent advances in bio-based multi-products of agricultural Jerusalem artichoke resources

The Jerusalem artichoke is a perennial plant that belongs to the sunflower family. As a non-grain crop, Jerusalem artichoke possesses a number of desirable characteristics that make it a valuable feedstock for biorefinery, such as inulin content, rapid growth, strong adaptability, and high yields. This review provides a comprehensive introduction to renewable Jerusalem artichoke-based biomass resources and recent advances in bio-based product conversion. Furthermore, we discuss the latest in the development of inulinase-producing microorganisms and enhanced inulin hydrolysis capacity of microbes by genetic engineering, which lead to a more cost-effective Jerusalem artichoke biorefinery. The review is aimed at promoting Jerusalem artichoke industry and new prospects for higher value-added production.

Cell wall integrity is required for pullulan biosynthesis and glycogen accumulation in Aureobasidium melanogenum P16

BACKGROUND

Pullulan and glycogen have many applications and physiological functions. However, to date, it has been unknown where and how the pullulan is synthesized in the yeast cells and if cell wall structure of the producer can affect pullulan and glycogen biosynthesis.

METHODS

The genes related to cell wall integrity were cloned, characterized, deleted and complemented. The cell wall integrity, pullulan biosynthesis, glycogen accumulation and gene expression were examined.

RESULTS

In this study, the GT6 and GT7 genes encoding different α1,2 mannosyltransferases in Aureobasidium melanogenum P16 were cloned and characterized. The proteins deduced from both the GT6 and GT7 genes contained the conserved sequences YNMCHFWSNFEI and YSTCHFWSNFEI of a Ktr mannosyltransferase family. The removal of each gene and both the two genes caused the changes in colony and cell morphology and enhanced glycogen accumulation, leading to a reduced pullulan biosynthesis and the declined expression of many genes related to pullulan biosynthesis. The swollen cells of the disruptants were due to increased accumulation of glycogen, suggesting that uridine diphosphate glucose (UDP-glucose) was channeled to glycogen biosynthesis in the disruptants, rather than pullulan biosynthesis. Complementation of the GT6 and GT7 genes in the corresponding disruptants and growth of the disruptants in the presence of 0.6 M KCl made pullulan biosynthesis, glycogen accumulation, colony and cell morphology be restored.

GENERAL SIGNIFICANCE

This is the first report that the two α1,2 mannosyltransferases were required for colony and cell morphology, glycogen accumulation and pullulan biosynthesis in the pullulan producing yeast.

The Genomes of Four Meyerozyma caribbica Isolates and Novel Insights into the Meyerozyma guilliermondii Species Complex

Yeasts of the Meyerozyma guilliermondii species complex are widespread in nature and can be isolated from a variety of sources, from the environment to arthropods to hospital patients. To date, the species complex comprises the thoroughly studied and versatile M. guilliermondii, the hard to distinguish M. caribbica, and Candida carpophila. Here we report the whole genome sequencing and de novo assembly of four M. caribbica isolates, identified with the most recent molecular techniques, derived from four Diptera species. The four novel assemblies present reduced fragmentation and comparable metrics (genome size, gene content) to the available genomes belonging to the species complex. We performed a phylogenomic analysis comprising all known members of the species complex, to investigate evolutionary relationships within this clade. Our results show a compact phylogenetic structure for the complex and indicate the presence of a sizable core set of genes. Furthermore, M. caribbica, despite a broad literature on the difficulties of discerning it from M. guilliermondii, seems to be more closely related to C. carpophila. Finally, we believe that there is evidence for considering these four genomes to be the first published for the species M. caribbica. Raw reads and assembled contigs have been made public to further the study of these organisms.

Candidacidal Activity of a Novel Killer Toxin from Wickerhamomyces anomalus against Fluconazole-Susceptible and -Resistant Strains

The isolation and characterization from the sand fly Phlebotomus perniciosus of a Wickerhamomyces anomalus yeast strain (Wa1F1) displaying the killer phenotype was recently reported. In the present work, the killer toxin (KT) produced by Wa1F1 was purified and characterized, and its antimicrobial activity in vitro was investigated against fluconazole- susceptible and -resistant clinical isolates and laboratory strains of Candida albicans and C. glabrata displaying known mutations. Wa1F1-KT showed a differential killing ability against different mutant strains of the same species. The results may be useful for the design of therapeutic molecules based on Wa1F1-KT and the study of yeast resistance mechanisms.

Single Cell Oil Production from Hydrolysates of Inulin by a Newly Isolated Yeast Papiliotrema laurentii AM113 for Biodiesel Making

Microbial oils are among the most attractive alternative feedstocks for biodiesel production. In this study, a newly isolated yeast strain, AM113 of Papiliotrema laurentii, was identified as a potential lipid producer, which could accumulate a large amount of intracellular lipids from hydrolysates of inulin. P. laurentii AM113 was able to produce 54.6% (w/w) of intracellular oil in its cells and 18.2 g/l of dry cell mass in a fed-batch fermentation. The yields of lipid and biomass were 0.14 and 0.25 g per gram of consumed sugar, respectively. The lipid productivity was 0.092 g of oil per hour. Compositions of the fatty acids produced were C_14:0 (0.9%), C_16:0 (10.8%), C_16:1 (9.7%), C_18:0 (6.5%), C_18:1 (60.3%), and C_18:2 (11.8%). Biodiesel obtained from the extracted lipids could be burnt well. This study not only provides a promising candidate for single cell oil production, but will also probably facilitate more efficient biodiesel production.

Cultivation-based strategies to find efficient marine biocatalysts

Marine bacteria have evolved to survive in the marine environment by using unique physiological, biochemical and metabolic features and the ability to produce enzymes and compounds which may have commercial value. The Azores archipelago presents several ecosystems with strong volcanic activity where bacteria thrive under e.g. high temperatures. In this study, samples collected in the island of São Miguel were screened for biocatalysts possessing e.g. lipase, esterase, amylase, and inulinase activities. After isolation of several hundred bacterial strains, high throughput screening methods allowed the fast identification of biocatalysts. The first cultivation tests were performed on 24-wells microtiter plates with online oxygen monitoring and bacteria able to grow within 24 h were selected for further process development. Bacteria able to produce the desired enzymes were selected for the first round of tests. Four Bacillus strains presented high inulinase activity. The next step in process development was the determination of key parameters for enzyme activity such as temperature, pH, salinity and substrate concentration. The highest inulinase activity, 2.2 g_sugars /g_protein h, was attained when the supernatant of a culture of a Bacillus subtilis strain was used in a magnetically stirred bioreactor. This study demonstrates how bacterial strains from marine environments may be used successfully in biotechnological processes.

Production, Purification, and Gene Cloning of a β-Fructofuranosidase with a High Inulin-hydrolyzing Activity Produced by a Novel Yeast Aureobasidium sp. P6 Isolated from a Mangrove Ecosystem

After screening of over 300 yeast strains isolated from the mangrove ecosystems, it was found that Aureobasidium sp. P6 strain had the highest inulin-hydrolyzing activity. Under the optimal conditions, this yeast strain produced an inulin-hydrolyzing activity of 30.98 ± 0.8 U/ml after 108 h of a 10-l fermentation. After the purification, a molecular weight of the enzyme which had the inulin-hydrolyzing activity was estimated to be 47.6 kDa, and the purified enzyme could actively hydrolyze both sucrose and inulin and exhibit a transfructosylating activity at 30.0 % sucrose, converting sucrose into fructooligosaccharides (FOS), indicating that the purified enzyme was a β-D-fructofuranosidase. After the full length of a β-D-fructofuranosidase gene (accession number KU308553) was cloned from Aureobasidium sp. P6 strain, a protein deduced from the cloned gene contained the conserved sequences MNDPNGL, RDP, ECP, FS, and Q of a glycosidehydrolase GH32 family, respectively, but did not contain a conserved sequence SVEVF, and the amino acid sequence of the protein from Aureobasidium sp. P6 strain had a high similarity to that of the β-fructofuranosidase from any other fungal strains. After deletion of the β-D-fructofuranosidase gene, the disruptant still had low inulin hydrolyzing and invertase activities and a trace amount of the transfructosylating activity, indicating that the gene encoding an inulinase may exist in the Aureobasidium sp. P6 strain.

Genetic Modification of the Marine-Isolated Yeast Aureobasidium melanogenum P16 for Efficient Pullulan Production from Inulin

In this study, in order to directly and efficiently convert inulin into pullulan, the INU1 gene from Kluyveromyces maximum KM was integrated into the genomic DNA and actively expressed in the high pullulan producer Aureobasidium melanogenum P16 isolated from the mangrove ecosystem. After the ability to produce pullulan from inulin by different transformants was examined, it was found that the recombinant strain EI36, one of the transformants, produced 40.92 U/ml of inulinase activity while its wild-type strain P16 only yielded 7.57 U/ml of inulinase activity. Most (99.27 %) of the inulinase produced by the recombinant strain EI36 was secreted into the culture. During the 10-l fermentation, 70.57 ± 1.3 g/l of pullulan in the fermented medium was attained from inulin (138.0 g/l) within 108 h, high inulinase activity (42.03 U/ml) was produced within 60 h, the added inulin was actively hydrolyzed by the secreted inulinase, and most of the reducing sugars were used by the recombinant strain EI36. This confirmed that the genetically engineered yeast of A. melanogenum strain P16 was suitable for direct pullulan production from inulin.

Optimization, kinetics, and modeling of inulinase production by K. marxianus var. marxianus

Pressmud, a by-product from the sugarcane industry, was used as a carbon source for the production of inulinase in solid-state fermentation (SSF). Statistical experimental designs were employed to screen the nutrients and optimize the media composition for the production of inulinase by Kluyveromyces marxianus var. marxianus. Eighteen various nutrients were selected for preliminary screening of production medium component by Plackett-Burman design (PBD) technique. Five nutrients were found to be significant for inulinase production and they were optimized by central composite design (CCD). The optimal media components for solid-state fermentation of inulinase using pressmud were (g/gds): corn steep liquor, 0.06072; urea, 0.01916; beef extract, 0.00957; FeSO4 · 7H2O, 0.00013; K2HPO4, 0.00441. The effect of moisture content and substrate concentration was also studied. From the results it was found that a maximum inulinase activity of 288 U/gds occurs at the moisture content of 65% and substrate concentration of 10 g. The constants in the Michaelis-Menten equation were evaluated and a high R (2) value implied the fitness of the model. Artificial neural network (ANN) modeling was also employed to predict the inulinase production.

Direct conversion of inulin into cell lipid by an inulinase-producing yeast Rhodosporidium toruloides 2F5

In this study, an inulinase-producing yeast strain 2F5 of Rhodosporidium toruloides was obtained. It was found that the yeast strain 2F5 could produce higher amount of oil from inulin and larger lipid bodies in its cells than any other yeast strains tested in this study. Under the optimal conditions, 62.14% (w/w) of lipid based on cell dry weight and 15.82g/l of the dry cell mass were produced from 6.0% (w/v) inulin at flask level, leaving 0.92% (w/v) of total sugar in the fermented medium. During 2-l fermentation, 70.36% (w/w) of lipid based on cell dry weight and 15.64g/l of the dry cell mass were produced from 6.0% (w/v) inulin. Over 99.09% of the fatty acids from the yeast strain 2F5 grown on inulin was C16:0, C18:0, C18:1 and C18:2, especially C18:1 (52.2%). The biodiesel prepared using the lipids produced by the yeast strain 2F5 could be burnt well.

Immobilization of inulinase on concanavalin A-attached super macroporous cryogel for production of high-fructose syrup

In this study, concanavalin A (Con A)-attached poly(ethylene glycol dimethacrylate) [poly(EGDMA)] cryogels were used for immobilization of Aspergillus niger inulinase. For this purposes, the monolithic cryogel column was prepared by radical cryocopolymerization of EGDMA as a monomer and N,N'-methylene bisacrylamide as a crosslinker. Then, Con A was attached by covalent binding onto amino-activated poly(EGDMA) cryogel via glutaraldehyde activation. Characterization of cryogels was performed by FTIR, EDX, and SEM studies. Poly(EGDMA) cryogels were highly porous and pore size was found to be approximately 50-100 μm. Con A-attached poly(EGDMA) cryogels was used in the adsorption of inulinase from aqueous solutions. Adsorption of inulinase on the Con A-attached poly(EGDMA) cryogel was performed in continuous system and the effects of pH, inulinase concentration, and flow rate on adsorption were investigated. The maximum amount of inulinase adsorption was calculated to be 27.85 mg/g cryogel at 1.0 mg/mL inulinase concentration and in acetate buffer at pH 4.0. Immobilized inulinase was effectively used in continuous preparation of high-fructose syrup. Inulin was converted to fructose in a continuous system and released fructose concentration was found to be 0.23 mg/mL at the end of 5 min of hydrolysis. High-fructose content of the syrup was demonstrated by thin layer chromatography.

Candida guilliermondii: biotechnological applications, perspectives for biological control, emerging clinical importance and recent advances in genetics

Candida guilliermondii (teleomorph Meyerozyma guilliermondii) is an ascomycetous species belonging to the Saccharomycotina CTG clade which has been studied over the last 40 years due to its biotechnological interest, biological control potential and clinical importance. Such a wide range of applications in various areas of fundamental and applied scientific research has progressively made C. guilliermondii an attractive model for exploring the potential of yeast metabolic engineering as well as for elucidating new molecular events supporting pathogenicity and antifungal resistance. All these research fields now take advantage of the establishment of a useful molecular toolbox specifically dedicated to C. guilliermondii genetics including the construction of recipient strains, the development of selectable markers and reporter genes and optimization of transformation protocols. This area of study is further supported by the availability of the complete genome sequence of the reference strain ATCC 6260 and the creation of numerous databases dedicated to gene ontology annotation (metabolic pathways, virulence, and morphogenesis). These genetic tools and genomic resources represent essential prerequisites for further successful development of C. guilliermondii research in medical mycology and in biological control by facilitating the identification of the multiple factors that contribute to its pathogenic potential. These genetic and genomic advances should also expedite future practical uses of C. guilliermondii strains of biotechnological interest by opening a window into a better understanding of the biosynthetic pathways of valuable metabolites.

Both decrease in ACL1 gene expression and increase in ICL1 gene expression in marine-derived yeast Yarrowia lipolytica expressing INU1 gene enhance citric acid production from inulin

In this study, some of the ATP-citrate lyase genes (ACL1) were deleted and the copy number of the iso-citrate lyase gene (ICL1) was increased in the marine-derived yeast Yarrowia lipolytica SWJ-1b displaying the recombinant inulinase. It was found that lipid content and iso-citric acid in the transformant 30 obtained were greatly reduced and citric acid production was greatly enhanced. It was also found that the ACL1 gene expression and ATP-citrate lyase activity in the transformant 30 were declined and the ICL1 gene expression and iso-citrate lyase activity were promoted. During the 2-l fermentation, 84.0 g/l of citric acid and 1.8 g/l of iso-citric acid in the fermented medium were attained from 10.0 % of inulin by the transformant 30 within 214 h. The results showed that only 0.36 % of the residual reducing sugar and 1.0 % of the residual total sugar were left in the fermented medium, suggesting that 89.6 % of the total sugar was used for citric acid production and cell growth by the transformant 30.

High level lipid production by a novel inulinase-producing yeast Pichia guilliermondii Pcla22

In this study, an inulinase-producing yeast strain Pcla22 of Pichia guilliermondii was identified. It was found that the yeast strain Pcla22 could produce higher amount of oil and more lipid bodies in its cells than any other yeast strains tested in this study. Under the optimal conditions, 60.6%(w/w) of lipid based on cell dry weight, 20.4 g/l of the dry cell mass, SCO produced per g of consumed sugar of 0.19 g/g and biomass produced per g of consumed sugar of 0.32 g/g were obtained in the culture of the yeast strain Pcla22 after 96 h of the fed-batch fermentation. Over 79.8% of the fatty acids from the yeast strain Pcla22 grown in the oil production medium containing inulin was C(16:0) and C(18:1), especially C(18:1) (57.9%). The biodiesel obtained from the produced lipid could be burnt well.

Thermotolerant Kluyveromyces marxianus and Saccharomyces cerevisiae strains representing potentials for bioethanol production from Jerusalem artichoke by consolidated bioprocessing

Thermotolerant inulin-utilizing yeast strains are desirable for ethanol production from Jerusalem artichoke tubers by consolidated bioprocessing (CBP). To obtain such strains, 21 naturally occurring yeast strains isolated by using an enrichment method and 65 previously isolated Saccharomyces cerevisiae strains were investigated in inulin utilization, extracellular inulinase activity, and ethanol fermentation from inulin and Jerusalem artichoke tuber flour at 40 °C. The strains Kluyveromyces marxianus PT-1 (CGMCC AS2.4515) and S. cerevisiae JZ1C (CGMCC AS2.3878) presented the highest extracellular inulinase activity and ethanol yield in this study. The highest ethanol concentration in Jerusalem artichoke tuber flour fermentation (200 g L(-1)) at 40 °C achieved by K. marxianus PT-1 and S. cerevisiae JZ1C was 73.6 and 65.2 g L(-1), which corresponded to the theoretical ethanol yield of 90.0 and 79.7 %, respectively. In the range of 30 to 40 °C, temperature did not have a significant effect on ethanol production for both strains. This study displayed the distinctive superiority of K. marxianus PT-1 and S. cerevisiae JZ1C in the thermotolerance and utilization of inulin-type oligosaccharides reserved in Jerusalem artichoke tubers. It is proposed that both K. marxianus and S. cerevisiae have considerable potential in ethanol production from Jerusalem artichoke tubers by a high temperature CBP.

Molecular characterization and expression of microbial inulinase genes

Many genes encoding exo- and endo-inulinases from bacteria, yeasts and filamentous fungi have been cloned and characterized. All the inulinases have several conserved motifs, such as WMND(E)PNGL, RDP, EC(V)P, SVEVF, Q and FS(T), which play an important role in inulinase catalysis and substrate binding. However, the exo-inulinases produced by yeasts has no conserved motif SVEVF and the yeasts do not produce any endo-inulinase. Exo- and endo-inulinases found in different microorganisms cluster separately at distant positions from each other. Most of the cloned inulinase genes have been expressed in Yarrowia lipolytica, Saccharomyces cerevisiae, Pichia pastoris, Klyuveromyces lactis and Escherichia coli, respectively. The recombinant inulinases produced and the engineered hosts using the cloned inulinase genes have many potential applications. Expression of most of the inulinase genes is repressed by glucose and fructose and induced by inulin and sucrose. However, the detailed mechanisms of the repression and induction are still unknown.

Experimental design of medium optimization for invertase production by Pichia sp

The culture medium requirement for invertase production by Pichia sp. was optimized and identified by initial screening method of Plackett-Burman. Furthermore, optimum concentrations of medium components, which were selected by in initial screening by Plackett-Burman, were determined by the Box-Behnken and its representative three-factor response-surface method. The regression models showed significantly high R (2) values of 97% for invertase activities, indicating that they are appropriate for predicting relationships between yeast extract, peptone and sucrose concentration with invertase production. According to the model the optimal concentrations of sucrose, yeast extract and peptone were 40, 5 and 4 g/ml, respectively. These predicted conditions were verified by validation experiments. In the optimized medium Pichia sp. produced invertase with activity of 38.71 U/ml, which is 4 times higher than that produced in original medium. Thus, this statistical approach enabled rapid identification and integration of key medium parameters for Pichia sp. BCCS M1, resulted the high invertase production.

Direct conversion of inulin and extract of tubers of Jerusalem artichoke into single cell oil by co-cultures of Rhodotorula mucilaginosa TJY15a and immobilized inulinase-producing yeast cells

In this study, it was found that the immobilized inulinase-producing cells of Pichia guilliermondii M-30 could produce 169.3 U/ml of inulinase activity while the free cells of the same yeast strain only produced 124.3 U/ml of inulinase activity within 48 h. When the immobilized inulinase-producing yeast cells were co-cultivated with the free cells of Rhodotorula mucilaginosa TJY15a, R. mucilaginosa TJY15a could accumulate 53.2% oil from inulin in its cells and cell dry weight reached 12.2g/l. Under the similar conditions, R. mucilaginosa TJY15a could accumulate 55.4% (w/w) oil from the extract of Jerusalem artichoke tubers in its cells and cell dry weight reached 12.8 g/l within 48 h. When the co-cultures were grown in 2l fermentor, R. mucilaginosa TJY15a could accumulate 56.6% (w/w) oil from the extract of Jerusalem artichoke tubers in its cells and cell dry weight reached 19.6g/l within 48 h. Over 90.0% of the fatty acids from the yeast strain TJY15a grown in the extract of Jerusalem artichoke tubers was C(16:0), C(18:1) and C(18:2), especially C(18:1) (50.6%).

Cloning of exo-β-1,3-glucanase gene from a marine yeast Williopsis saturnus and its overexpression in Yarrowia lipolytica

The exo-β-1,3-glucanase structural gene (WsEXG1 gene, accession number: FJ875997.2) was isolated from both the genomic DNA and cDNA of the marine yeast Williopsis saturnus WC91-2 by inverse PCR and RT-PCR. An open reading frame of 1,254 bp encoding a 417 amino acid protein (isoelectric point: 4.5) with calculated molecular weight of 46.2 kDa was characterized. The promoter of the gene (intronless) was located from -28 to -77 and had one TATA box while its terminator contained the sequence AAGAACAATAAACAA from +1,386 to +1,401. The protein had the Family 5 glycoside hydrolase signature IGLELLNEPL and a fragment with the sequence of NLCGEWSAA, where the Glu-310 (E) was considered to be the catalytic nucleophile. The WsEXG1 gene was overexpressed in Yarrowia lipolytica Po1h and the recombinant WsEXG1 was purified and characterized. The molecular weight of the purified rWsEXG1 was 46.0 kDa. The optimal pH and temperature of the purified rWsEXG1 were 5.0°C and 40°C, respectively. The purified rWsEXG1 had high exo-β-1,3-glucanase activity. Therefore, the recombinant β-1,3-glucanase may have highly potential applications in food and pharmaceutical industries.

Biotechnological potential of inulin for bioprocesses

Inulin consists of linear chains of β-2,1-linked D-fructofuranose molecules terminated by a glucose residue through a sucrose-type linkage at the reducing end. In this review article, inulin and its applications in bioprocesses are overviewed. The tubers of many plants, such as Jerusalem artichoke, chicory, dahlia, and yacon contain a large amount of inulin. Inulin can be actively hydrolyzed by microbial inulinases to produce fructose, glucose and inulooligosaccharides (IOS). The fructose and glucose formed can be further transformed into ethanol, single-cell protein, single cell oil and other useful products by different microorganisms. IOS formed have many functions. Therefore, inulin can be widely used in food, feed, pharmaceutical, chemical and biofuels industries.