Characteristics of copper tolerance in Yarrowia lipolytica

Experimental validation off-line a nonlinear controller for removal of chromium using non-living cells of Yarrowia lipolytica

The removal of hexavalent chromium [Cr (VI)] using non-living cells of Yarrowia lipolytica was investigated. Batch and continuous studies on removal of Cr (VI) achieved 97% and 99% removal from aqueous phase, respectively. The specific uptake values at pH of 2 in batch process were 40.73 ± 1.3 mg/g and 30.09 ± 0.23 mg/g on non-living cells, when 100 and 200 mg/L of metal Cr (VI) concentrations were used. In order to investigate the regulation of Cr (VI) under continuous operation based on reaction volume numerically a new class of feedback controller from structure polynomial was designed. The proposed methodology was used to an experimentally kinetic model for a removal Cr (VI) from Yarrowia lipolytica biomass was showed satisfactory closed-loop performance the proposed controller. Starting from an off-line optimization performed in simulation, we present the controller implementation, focussing on the methodology required to could be suitable for implementation in real time. In our experimental results, we highlight some discrepancies between simulation and reality despite these differences, the controller managed to perform convergence to removal Cr (VI). Finally, the results validated with off-line samples suggest that the proposed control could be suitable for in application in potential scenarios for wastewater treatment.

Identification and Characterization of Dmct: A Cation Transporter in Yarrowia lipolytica Involved in Metal Tolerance

Yarrowia lipolytica is a dimorphic fungus used as a model organism to investigate diverse biotechnological and biological processes, such as cell differentiation, heterologous protein production, and bioremediation strategies. However, little is known about the biological processes responsible for cation concentration homeostasis. Metals play pivotal roles in critical biochemical processes, and some are toxic at unbalanced intracellular concentrations. Membrane transport proteins control intracellular cation concentrations. Analysis of the Y. lipolytica genome revealed a characteristic functional domain of the cation efflux protein family, i.e., YALI0F19734g, which encodes YALI0F19734p (a putative Yl-Dmct protein), which is related to divalent metal cation tolerance. We report the in silico analysis of the putative Yl-Dmct protein's characteristics and the phenotypic response to divalent cations (Ca²⁺, Cu²⁺, Fe²⁺, and Zn²⁺) in the presence of mutant strains, Δdmct and Rdmct, constructed by deletion and reinsertion of the DMCT gene, respectively. The absence of the Yl-Dmct protein induces cellular and growth rate changes, as well as dimorphism differences, when calcium, copper, iron, and zinc are added to the cultured medium. Interestingly, the parental and mutant strains were able to internalize the ions. Our results suggest that the protein encoded by the DMCT gene is involved in cell development and cation homeostasis in Y. lipolytica.

Copper Ion Mediates Yeast-to-Hypha Transition in Yarrowia lipolytica

Copper is an essential element that maintains yeast physiological function at low concentrations, but is toxic in excess. This study reported that Cu(II) significantly promoted the yeast-to-hypha transition of Yarrowia lipolytica in dose-dependent manner. Strikingly, the intracellular Cu(II) accumulation was drastically reduced upon hyphae formation. Moreover, we investigated the effect of Cu(II) on the physiological function of Y. lipolytica during the dimorphic transition and found that cellular viability and thermomyces lanuginosus lipase (TLL) were both influenced by the Cu(II)-induced yeast-to-hypha transition. Overall, hyphal cells survived better than yeast-form cells with copper ions. Furthermore, transcriptional analysis of the Cu(II)-induced Y. lipolytica before and after hyphae formation revealed a transition state between them. The results showed multiple differentially expressed genes (DEGs) were turned over between the yeast-to-transition and the transition-to-hyphae processes. Furthermore, gene set enrichment analysis (GSEA) identified that multiple KEGG pathways, including signaling, ion transport, carbon and lipid metabolism, ribosomal, and other biological processes, were highly involved in the dimorphic transition. Importantly, overexpression screening of more than thirty DEGs further found four novel genes, which are encoded by YALI1_B07500g, YALI1_C12900g, YALI1_E04033g, and YALI1_F29317g, were essential regulators in Cu-induced dimorphic transition. Overexpression of each of them will turn on the yeast-to-hypha transition without Cu(II) induction. Taken together, these results provide new insight to explore further the regulatory mechanism of dimorphic transition in Y. lipolytica.

Selection of Producer of α-Ketoglutaric Acid from Ethanol-Containing Wastes and Impact of Cultivation Conditions

Ester–aldehyde fraction (EAF) is a by-product of ethyl-alcohol-producing companies whose purification requires an expensive process. The results of this study illustrate the environmentally friendly and alternative possibility of using EAF to increase their value as substrate to produce α-ketoglutaric acid (KGA) using different yeasts. It was found that some species of the genera Babjeviella, Diutina, Moesziomyces, Pichia, Saturnispora, Sugiyamaella, Yarrowia and Zygoascus grown under thiamine deficiency accumulate KGA in the medium with an EAF as the sole carbon source. The strain Y. lipolytica VKM Y-2412 was selected as the producer. To reach the maximum production of KGA, the cultivation medium should contain 0.3 µg/L thiamine during cultivation in flasks and 2 µg/L in the fermentor; the concentration of (NH4)2SO4 should range from 3 to 6 g/L; and the optimal concentrations of Zn2+, Fe2+ and Cu2+ ions should be 1.2, 0.6 and 0.05 mg/L, respectively. EAF concentration should not exceed 1.5 g/L in the growth phase and 3 g/L in the KGA synthesis phase. At higher EAF concentrations, acetic acid was accumulated and inhibited yeast growth and KGA production. Under optimal conditions, the producer accumulated 53.8 g/L KGA with a yield (Yp/s) of 0.68 g/g substrate consumed.

A comprehensive assessment of Yarrowia lipolytica and its interactions with metals: Current updates and future prospective

The non-conventional yeast Yarrowia lipolytica has been popular as a model system for understanding biological processes such as dimorphism and lipid accumulation. The organism can efficiently utilize hydrophobic substrates (hydrocarbons and triglycerides) thereby rendering it relevant in bioremediation of oil polluted environments. The current review focuses on the interactions of this fungus with metal pollutants and its potential application in bioremediation of metal contaminated locales. This fungus is intrinsically equipped with a variety of physiological and biochemical features that enable it to tide over stress conditions induced by the presence of metals. Production of enzymes such as phosphatases, reductases and superoxide dismutases are worth a special mention. In the presence of metals, levels of inherently produced metal binding proteins (metallothioneins) and the pigment melanin are seen to be elevated. Morphological alterations with respect to biofilm formation and dimorphic transition from yeast to mycelial form are also induced by certain metals. The biomass of Y. lipolytica is inherently important as a biosorbent and cell surface modification, process optimization or whole cell immobilization techniques have aided in improving this capability. In the presence of metals such as mercury, cadmium, copper and uranium, the culture forms nanoparticulate deposits. In addition, on account of its intrinsic reductive ability, Y. lipolytica is being exploited for synthesizing nanoparticles of gold, silver, cadmium and selenium with applications as antimicrobial compounds, location agents for bioimaging and as feed supplements. This versatile organism thus has great potential in interacting with various metals and addressing problems related to their pollutant status.

A Yarrowia lipolytica Strain Engineered for Pyomelanin Production

The yeast Yarrowia lipolytica naturally produces pyomelanin. This pigment accumulates in the extracellular environment following the autoxidation and polymerization of homogentisic acid, a metabolite derived from aromatic amino acids. In this study, we used a chassis strain optimized to produce aromatic amino acids for the de novo overproduction of pyomelanin. The gene 4HPPD, which encodes an enzyme involved in homogentisic acid synthesis (4-hydroxyphenylpyruvic acid dioxygenase), was characterized and overexpressed in the chassis strain with up to three copies, leading to pyomelanin yields of 4.5 g/L. Homogentisic acid is derived from tyrosine. When engineered strains were grown in a phenylalanine-supplemented medium, pyomelanin production increased, revealing that the yeast could convert phenylalanine to tyrosine, or that the homogentisic acid pathway is strongly induced by phenylalanine.

Yarrowia lipolytica: a multitalented yeast species of ecological significance

Yarrowia lipolytica is characterized by GRAS (Generally regarded as safe) status, the versatile substrate utilization profile, rapid utilization rates, metabolic diversity and flexibility, the unique abilities to tolerate to extreme environments (acidic, alkaline, hypersaline, heavy metal-pollutions and others) and elevated biosynthesis and secreting capacities. These advantages of Y. lipolytica allow us to consider it as having great ecological significance. Unfortunately, there is still a paucity of relevant review data. This mini-review highlights ecological ubiquity of Y. lipolytica species, their ability to diversify and colonize specialized niches. Different Y. lipolytica strains, native and engineered, are beneficial in degrading many environmental pollutants causing serious ecological problems worldwide. In agriculture has a potential to be a bio-control agent by stimulating plant defense response, and an eco-friendly bio-fertilizer. Engineered strains of Y. lipolytica have become a very promising platform for eco-friendly production of biofuel, commodities, chemicals and secondary metabolites of plant origin, obtaining which by other method were limited or economically infeasible, or were accompanied by stringent environmental problems. Perspectives to use potential of Y. lipolytica's capacities for industrial scale production of valuable compounds in an eco-friendly manner are proposed.

Gene Expression Analysis of Three Putative Copper-Transporting ATPases in Copper-Tolerant Fibroporia radiculosa

Copper tolerance of brown-rot basidiomycete decay fungi can lessen the efficacy of copper-containing wood preservatives for wood products in-service. The purpose of this study was to evaluate wood mass loss and differential expression of three genes that have putative annotations for copper-transporting ATPase pumps (FIBRA_00974, FIBRA_04716, and FIBRA_01430). Untreated southern pine (SP) and SP treated with three concentrations of ammoniacal copper citrate (CC, 0.6, 1.2, and 2.4%) were exposed to two copper-tolerant Fibroporia radiculosa isolates (FP-90848-T and L-9414-SP) and copper-sensitive Gloeophyllum trabeum isolate (MAD 617) in a 4-week-long standard decay test (AWPA E10-19). Decay of copper-treated wood was inhibited by G. trabeum (p = 0.001); however, there was no inhibition of decay with increasing copper concentrations by both F. radiculosa isolates. Initially, G. trabeum and one F. radiculosa isolate (L-9414-SP) highly upregulated FIBRA_00974 and FIBRA_04716 on copper-treated wood at week 1 (p = 0.005), but subsequent expression was either not detected or was similar to expression on untreated wood (p = 0.471). The other F. radiculosa isolate (FP-90848-T) downregulated FIBRA_00974 (p = 0.301) and FIBRA_04716 (p = 0.004) on copper-treated wood. FIBRA_01430 expression by G. trabeum was not detected, but was upregulated by both F. radiculosa FP-90848-T (p = 0.481) and L-9414-SP (p = 0.392). Results from this study suggest that all three test fungi utilized different mechanisms when decaying copper-treated wood. Additionally, results from this study do not provide support for the involvement of these putative gene annotations for copper-transporting ATPase pumps in the mechanism of copper-tolerance.

Removal of uranium by immobilized biomass of a tropical marine yeast Yarrowia lipolytica

A marine yeast, Yarrowia lipolytica isolated from an oil polluted sea water and shown earlier to sequester dissolved uranium (U) at pH 7.5, was utilized in the present study for developing an immobilized-cell process for U removal from aqueous solutions under batch and continuous flow through systems. In batch system, optimum biosorption conditions for U removal were assessed by investigating the effects of biomass dose, initial U concentration, contact time and pH of solution using Y. lipolytica cells immobilized in calcium alginate beads. Appreciable uranium-binding capabilities over a wide pH range (3-9) were observed with the alginate beads bearing yeast cells. Out of Langmuir and Freundlich models employed for describing the sorption equilibrium data under batch mode, uranyl adsorption followed Langmuir approach with satisfactory correlation coefficient higher than 0.9. Uranyl adsorption kinetics by Y. lipolytica entrapped in alginate beads was best described by the pseudo-second-order model. While the environmental scanning electron microscopy established the immobilization and the uniform distribution of Y. lipolytica cells in the alginate beads, the Energy Dispersive X-ray spectroscopy analysis confirmed the deposition of U in the beads following their exposure to uranyl solution. Fixed bed flow-through column comprising of Y. lipolytica biomass immobilized in polyacrylamide matrix displayed high efficacy for continuous removal of uranium at pH 7.5 up to five adsorption-desorption cycles. Adsorbed U by immobilized cells could be significantly desorbed using 0.1 N HCl. Overall, our results present the superior efficiency of immobilized Y. lipolytica biomass for U removal using batch and regenerative approaches.

Improving ionic liquid tolerance in Saccharomyces cerevisiae through heterologous expression and directed evolution of an ILT1 homolog from Yarrowia lipolytica

Ionic liquids show promise for deconstruction of lignocellulosic biomass prior to fermentation. Yet, imidazolium ionic liquids (IILs) can be toxic to microbes even at concentrations present after recovery. Here, we show that dominant overexpression of an Ilt1p homolog (encoded by YlILT1/YALI0C04884) from the IIL-tolerant yeast Yarrowia lipolytica confers an improvement in 1-ethyl-3-methylimidazolium acetate tolerance in Saccharomyces cerevisiae compared to the endogenous Ilt1p (ScILT1/YDR090C). We subsequently enhance tolerance in S. cerevisiae through directed evolution of YlILT1 using growth-based selection, leading to identification of mutants that grow in up to 3.5% v/v ionic liquid. Lastly, we demonstrate that strains expressing YlILT1 variants demonstrate improved growth rate and ethanol production in the presence of residual IIL. This shows that dominant overexpression of a heterologous protein (wild type or evolved) from an IIL-tolerant yeast can increase tolerance in S. cerevisiae at concentrations relevant to bioethanol production from IIL-treated biomass.

Relationship between salt tolerance and nanoparticle synthesis by Williopsis saturnus NCIM 3298

This work describes cell associated and extracellular synthesis of nanoparticles by the yeast, Williopsis saturnus. The yeast was able to grow in the absence and presence of sodium chloride (NaCl) and form nanoparticles in a cell associated manner. The content of melanin, a stress-associated pigment was found to be progressively greater in the presence of increasing concentrations of NaCl. With higher quantities of melanin (extracted from yeast cells grown in the presence of 4% of NaCl), smaller sized nanoparticles were obtained. This is the first report on understanding the relationship between halotolerance, production of a stress-related pigment (melanin) and synthesis of nanoparticles with antioxidant properties by using W. saturnus as a model system. The cell free extracts derived from cultures grown in the absence of NaCl were able to mediate extracellular synthesis of gold and silver nanoparticles and the biomolecule mediating nanoparticle synthesis was identified to be a glycolipid. Extracellularly synthesized gold nanoparticles displayed good catalytic activity and rapidly mediated the reduction of 4-nitrophenol to 4-aminophenol.

Copper Resistance in Aspergillus nidulans Relies on the PI-Type ATPase CrpA, Regulated by the Transcription Factor AceA

Copper homeostasis has been extensively studied in mammals, bacteria, and yeast, but it has not been well-documented in filamentous fungi. In this report, we investigated the basis of copper tolerance in the model fungus Aspergillus nidulans. Three genes involved in copper homeostasis have been characterized. First, crpA the A. nidulans ortholog of Candida albicans CaCRP1 gene encoding a P_I-type ATPase was identified. The phenotype of crpA deletion led to a severe sensitivity to Cu⁺² toxicity and a characteristic morphological growth defect in the presence of high copper concentration. CrpA displayed some promiscuity regarding metal species response. The expression pattern of crpA showed an initial strong elevation of mRNA and a low continuous gene expression in response to long term toxic copper levels. Coinciding with maximum protein expression level, CrpA was localized close to the cellular surface, however protein distribution across diverse organelles suggests a complex regulated trafficking process. Secondly, aceA gene, encoding a transcription factor was identified and deleted, resulting in an even more extreme copper sensitivity than the ΔcrpA mutant. Protein expression assays corroborated that AceA was necessary for metal inducible expression of CrpA, but not CrdA, a putative metallothionein the function of which has yet to be elucidated.

Characterization of calcineurin from Cryptococcus humicola and the application of calcineurin in aluminum tolerance

BACKGROUND

Calcineurin (CaN) is a Ca2+- and calmodulin (CaM)-dependent serine/threonine phosphatase. Previous studies have found that CaN is involved in the regulation of the stress responses.

RESULTS

In this study, the growth of Cryptococcus humicola was inhibited by the CaN inhibitor tacrolimus (FK506) under aluminum (Al) stress. The expression of CNA encoding a catalytic subunit A (CNA) and its interaction with CaM were upregulated when the concentration of Al was increased. A CaM-binding domain and key amino acids responsible for interaction with CaM were identified. ∆CNAb with a deletion from S454 to A639 was detected to bind to CaM, while ∆CNAa with a deletion from R436 to A639 showed no binding to CaM. The binding affinities of CNA1 and CNA2, in which I439 or I443 were replaced by Ala, were decreased relative to wild-type CNA. The phosphatase activities of ∆CNAa, CNA1 and CNA2 were lower than the wild-type protein. These results suggest that the region between R436 and S454 is essential for the interaction with CaM and I439, I443 are key amino acids in this region. The ability of the CNA transgenic yeast to develop resistance to Al was significantly higher than that of control yeast. Residual Al in the CNA transgenic yeast culture media was significantly lower than the amount of Al originally added to the media or the residual Al remaining in the control yeast culture media. These findings suggest that CNA confers Al tolerance, and the mechanism of Al tolerance may involve absorption of active Al.

CONCLUSIONS

Al stress up-regulated the expression of CNA. CaM-binding domain and key amino acids responsible for interaction with CaM were identified and both are required for phosphatase activities. CNA conferred yeast Al resistance indicating that the gene has a potential to improve Al-tolerance through gene engineering.

Effect of aluminum stress on the expression of calmodulin and the role of calmodulin in aluminum tolerance

Calmodulin (CaM) is a calcium ion-binding protein that regulates a variety of cellular functions through its downstream target proteins. Previous studies have reported that overexpression of CaM enhances tolerance to stress, including resistance to salt, heat, cold, drought and plant pathogens. In this study, the growth of Cryptococcus humicola was inhibited by the CaM inhibitor, trifluoperazine, under aluminum (Al) stress. The expression of CaM of C. humicola (ChCaM) was upregulated when the concentration and treatment time with Al was increased. These results indicate that Al stress affects the transcription and translation of ChCaM and that ChCaM may play an important role in Al tolerance. Transgenic ChCaM Saccharomyces cerevisiae was constructed and designated as Sc-ChCaM. The ability of Sc-ChCaM to develop resistance to Al was significantly higher than that of control yeast containing the empty vector pYES3/CT designated as Sc. The residual Al content in the medium containing ChCaM transgenic yeast in culture was significantly lower than the initial amount of Al added in the medium or the residual Al content in the medium containing the control yeast in culture. This finding suggests that ChCaM confers Al tolerance in transgenic yeast, and the absorption of active Al from the culture may be one reason for Al tolerance. These results indicate that ChCaM may be a candidate gene for Al tolerance in engineered plants.

Yarrowia lipolytica and pollutants: Interactions and applications

Yarrowia lipolytica is a dimorphic, non-pathogenic, ascomycetous yeast species with distinctive physiological features and biochemical characteristics that are significant in environment-related matters. Strains naturally present in soils, sea water, sediments and waste waters have inherent abilities to degrade hydrocarbons such as alkanes (short and medium chain) and aromatic compounds (biphenyl and dibenzofuran). With the application of slow release fertilizers, design of immobilization techniques and development of microbial consortia, scale-up studies and in situ applications have been possible. In general, hydrocarbon uptake in this yeast is mediated by attachment to large droplets (via hydrophobic cell surfaces) or is aided by surfactants and emulsifiers. Subsequently, the internalized hydrocarbons are degraded by relevant enzymes innately present in the yeast. Some wild-type or recombinant strains also detoxify nitroaromatic (2,4,6-trinitrotoluene), halogenated (chlorinated and brominated hydrocarbons) and organophosphate (methyl parathion) compounds. The yeast can tolerate some metals and detoxify them via different biomolecules. The biomass (unmodified, in combination with sludge, magnetically-modified and in the biofilm form) has been employed in the biosorption of hexavalent chromium ions from aqueous solutions. Yeast cells have also been applied in protocols related to nanoparticle synthesis. The treatment of oily and solid wastes with this yeast reduces chemical oxygen demand or value-added products (single cell oil, single cell protein, surfactants, organic acids and polyalcohols) are obtained. On account of all these features, the microorganism has established a place for itself and is of considerable value in environment-related applications.

Mineral supplementation increases erythrose reductase activity in erythritol biosynthesis from glycerol by Yarrowia lipolytica

The aim of this study was to examine the impact of divalent copper, iron, manganese, and zinc ions on the production of erythritol from glycerol by Yarrowia lipolytica and their effect on the activity of erythrose reductase. No inhibitory effect of the examined minerals on yeast growth was observed in the study. Supplementation with MnSO₄·7H₂O (25 mg l⁻¹) increased erythritol production by Y. lipolytica by 14.5 %. In the bioreactor culture with manganese ion addition, 47.1 g l⁻¹ of erythritol was produced from 100.0 g l⁻¹ of glycerol, which corresponded to volumetric productivity of 0.87 g l⁻¹ h⁻¹. The addition of Mn²⁺ enhanced the intracellular activity of erythrose reductase up to 24.9 U g⁻¹ of dry weight of biomass (DW), hence, about 1.3 times more than in the control.

Formation and tunable disassembly of polyelectrolyte-Cu2+ layer-by-layer complex film

Layer-by-layer assembly of films containing metal ions was investigated. A complex between various metal ions and branched polyethyleneimine is formed in solution and then assembled into multilayer films with poly(acrylic acid). The metal-ligand complex formation results in brightly colored materials that deposit as thick layers. Cu(2+)-containing films were chosen as a model for studying the disassembly of these films in response to various stimuli, including pH, salt, and surfactants. The range of pH instability corresponds to the pH range over which pores are formed in the film. We demonstrate controllable disassembly of these materials, which could be used for antifungal or antibacterial applications.

Psychrotrophic yeast Yarrowia lipolytica NCYC 789 mediates the synthesis of antimicrobial silver nanoparticles via cell-associated melanin

A psychrotrophic marine strain of the ascomycetous yeast Yarrowia lipolytica (NCYC 789) synthesized silver nanoparticles (AgNPs) in a cell-associated manner. These nanostructures were characterized by UV-Visible spectroscopy and scanning electron microscope-energy dispersive spectrometer (SEM-EDS) analysis. The brown pigment (melanin) involved in metal-interactions was obtained from the cells. This extracted pigment also mediated the synthesis of silver nanoparticles that were characterized by a variety of analytical techniques. The melanin-derived nanoparticles displayed antibiofilm activity. This paper thus reports the synthesis of AgNPs by the biotechnologically important yeast Y. lipolytica; proposes a possible mechanism involved in the synthetic process and describes the use of the bio-inspired nanoparticles as antibiofilm agents.

3, 4-dihydroxy-L-phenylalanine-derived melanin from Yarrowia lipolytica mediates the synthesis of silver and gold nanostructures

Background

Nanobiotechnology applies the capabilities of biological systems in generating a variety of nano-sized structures. Plants, algae, fungi and bacteria are some systems mediating such reactions. In fungi, the synthesis of melanin is an important strategy for cell-survival under metal-stressed conditions. Yarrowia lipolytica, the biotechnologically significant yeast also produces melanin that sequesters heavy metal ions. The content of this cell-associated melanin is often low and precursors such as L-tyrosine or 3, 4-dihydroxy-L-phenylalanine (L-DOPA) can enhance its production. The induced melanin has not been exploited for the synthesis of nanostructures. In this investigation, we have employed L-DOPA-melanin for the facile synthesis of silver and gold nanostructures. The former have been used for the development of anti-fungal paints.

Methods

Yarrowia lipolytica NCIM 3590 cells were incubated with L-DOPA for 18 h and the resultant dark pigment was subjected to physical and chemical analysis. This biopolymer was used as a reducing and stabilizing agent for the synthesis of silver and gold nanostructures. These nanoparticles were characterized by UV-Visible spectra, X-ray diffraction (XRD) studies, and electron microscopy. Silver nanoparticles were evaluated for anti-fungal activity.

Results

The pigment isolated from Y. lipolytica was identified as melanin. The induced pigment reduced silver nitrate and chloroauric acid to silver and gold nanostructures, respectively. The silver nanoparticles were smaller in size (7 nm) and displayed excellent anti-fungal properties towards an Aspergillus sp. isolated from a wall surface. An application of these nanoparticles as effective paint-additives has been demonstrated.

Conclusion

The yeast mediated enhanced production of the metal-ion-reducing pigment, melanin. A simple and rapid method for the extracellular synthesis of nanoparticles with paint-additive-application was developed.

Proteomic study of the yeast Rhodotorula mucilaginosa RCL-11 under copper stress

In order to understand the mechanism involved in Rhodotorula mucilaginosa RCL-11 resistance to copper a proteomic study was conducted. Atomic absorption spectroscopy showed that the copper concentration in the medium decreased from 0.5 to 0.19 mM 48 h after inoculation of the yeast. Analysis of one-dimensional gel electrophoresis of crude cell extracts revealed expression of differential bands between cells with and without copper. In order to study this difference, two-dimensional electrophoresis of R. mucilaginosa RCL-11 exposed to Cu for 16, 24, and 48 h was carried out. Identification of differentially expressed proteins was performed by MALDI-TOF/TOF. Ten of the 16 spots identified belonged to heat shock proteins. Superoxide dismutase, methionine synthase and beta-glucosidase were also found over-expressed at high copper concentrations. The results obtained in the present work show that when R. mucilaginosa RCL-11 is exposed to 0.5 mM copper, differential proteins, involved in cell resistance mechanisms, are expressed.

The construction of a new integrative vector with a new selective marker of copper resistance for glycerol producer Candida glycerinogenes

Candida glycerinogenes WL2002-5 has been used for industrial-scale fermentation of glycerol and may be a promising genetic host due to its tolerance to high osmotic pressure and fast growth. It resists many kinds of drugs, such as G418/hygromycin/cycloheximide. In previous studies, only Zeocin was used as a drug-resistant marker. But Zeocin is so expensive that it largely limits the genetic and molecular study. Here, we constructed a eukaryotic integrative vector pGAPZU, based on pGAPZB, to gain a new selectable marker of copper resistance for this strain. The results showed that the CUP1 gene of Saccharomyces cerevisiae elevated copper resistance of C. glycerinogenes. The C. glycerinogenes transformed with recombinant vector pGUC, obtained from introducing CUP1 gene into plasmid pGAPZU, could resist 21 mM copper, while the minimum inhibitory concentration (MIC) of wild type was 18 mM in solid YEPD medium. With copper resistance as a selective marker, research cost was largely reduced from 114.0 $/L with Zeocin as selective marker to 0.1 $/L. The new expression vector pGUC and selective marker of copper resistance gene establish a good foundation for further study on this industrial strain.

Removal of chromium (VI) ions from aqueous solution by adsorption onto two marine isolates of Yarrowia lipolytica

The removal of chromium (VI) ions from aqueous solutions by the biomass of two marine strains of Yarrowia lipolytica (NCIM 3589 and 3590) was studied with respect to pH, temperature, biomass, sea salt concentration, agitation speed, contact time and initial concentration of chromium (VI) ions. Maximum biosorption was observed at pH 1.0 and at a temperature of 35 degrees C. Increase in biomass and sea salts resulted in a decreased metal uptake. With an agitation speed of 130 rpm, equilibrium was attained within 2h. Under optimum conditions, biosorption was enhanced with increasing concentrations of Cr (VI) ions. NCIM 3589 and 3590 displayed a specific uptake of Cr (VI) ions of 63.73+/-1.3 mg g(-1) at a concentration of 950 ppm and 46.09+/-0.23 mg g(-1) at 955 ppm, respectively. Scatchard plot analysis revealed a straight line allowing the data to be fitted in the Langmuir model. The adsorption data obtained also fitted well to the Freundlich isotherm. The surface sequestration of Cr (VI) by Y. lipolytica was investigated with a scanning electron microscope equipped with an energy dispersive spectrometer (SEM-EDS) as well as with ED-X-ray fluorescence (ED-XRF). Fourier transform infrared (FTIR) spectroscopy revealed the involvement of carboxyl, hydroxyl and amide groups on the cell surfaces in chromium binding.

Responses of Candida fukuyamaensis RCL-3 and Rhodotorula mucilaginosa RCL-11 to copper stress

The effect of high Cu(II) concentrations on superoxide dismutase (SOD) and catalase (CAT) activity in Candida fukuyamaensis RCL-3 and Rhodotorula mucilaginosa RCL-11, previously isolated from a copper filter at a mine plant in Argentina, was studied. Addition of 0.1, 0.2 and 0.5 mM Cu(II) to the culture medium increased total SOD and CAT activity in both strains. Native polyacrylamide gel electrophoresis revealed two bands with SOD activity for C. fukuyamaensis RCL-3 and only one for R. mucilaginosa RCL-11; the three bands corresponded to MnSOD.Intracellular accumulation of copper and morphological changes was observed using electron microscopy. Dark bodies examined with transmission electron microscopy (TEM) after 48 h of incubation probably corresponded to copper deposits. The number of dark bodies in R. mucilaginosa RCL-11 grew with increasing incubation time, whereas in C. fukuyamaensis RCL-3 the amount decreased. Scanning electron micrographs (SEM) of C. fukuyamaensis RCL-3 did not reveal any differences compared with the control, but R. mucilaginosa RCL-11 cells were bigger than control ones. TEM confirmed absence of compartmentalization mechanisms in Cu(II) detoxification since electron-dense bodies were mainly found in the cytoplasm.