Iron enriched yeast biomass--a promising mineral feed supplement

Investigation of impact of siderophore and process variables on production of iron enriched Saccharomyces boulardii by Plackett-Burman design

The primary cause of anemia worldwide is due to poor diet and iron deficiency. Iron (Fe) enriched yeast can be the most effective way to manage anemia because of the capability for biotransformation of mineral to organic and bioavailable iron. To overcome the low richness of yeast, the use of siderophore as cellular iron carriers is a new approach. In this research, for the first time the potential of siderophore in increasing the Fe enrichment of Saccharomyces boulardii (S. boulardii), which is important because of its probiotic properties and resistance to different stresses, has been investigated to produce of potential iron supplements. For this purpose, siderophore was produced by Pseudomonas aeruginosa (P. aeruginosa). Siderophore impact, along with ten other independent process variables, has been studied on the efficiency of iron biotransformation by the Plackett-Burman design (PBD). The results showed that the highest biotransformation yield was 17.77 mg Fe/g dry cell weight (DCW) in the highest biomass weight of 9 g/l. Iron concentration is the most important variable, with contributions of 46% and 70.79% for biomass weight and biotransformation, respectively, followed by fermentation time, agitation speed, and KH2PO4 concentration. But increasing the level of siderophore and zinc led to a significant negative effect. siderophore inefficiency may be attributed to the absence of membrane receptors for pyoverdine (Pvd) and pyochelin (Pch) siderophores. Also, the steric hindrance of the cell wall mannan, the stickiness and sediment ability of the yeast, can create limitations in the absorption of elements. Such yeast can be used as a potential source of iron even for vegetarians and vegans in the form of medicinal and fortified food products to improve the treatment of anemia. It is recommended that further research be focused on increasing the iron enrichment of yeast by overcoming the structural barrier of the cell wall, investigating factors affecting membrane permeability and iron transport potential of other types of siderophores.

Production of iron-enriched yeast and it's application in the treatment of iron-deficiency anemia

Iron deficiency anemia (IDA) is one of the most serious forms of malnutrition. Wild type strains of Saccharomyces cerevisiae have higher tolerance to inorganic iron and higher iron conversion and accumulation capacity. The aim of this study was to investigate the effect of S. cerevisiae enriched iron as a potential organic iron supplement on mice with iron deficiency anemia. 60 male Kunming mice (KM mice, with strong adaptability and high reproduction rate, it can be widely used in pharmacology, toxicology, microbiology and other research) were randomly divided into normal control group and iron deficiency diet model group to establish IDA model. After the model was established, IDA mice were randomly divided into 5 groups: normal control group, IDA group, organic iron group (ferrous glycinate), inorganic iron group (ferrous sulfate) and S. cerevisiae enriched iron group. Mice in the experimental group were given different kinds of iron by intragastric administration once a day for 4w. The results showed that S. cerevisiae enriched iron had an effective recovery function, and the body weight and hematological parameters of IDA mice returned to normal levels. The activities of superoxide dismutase, glutathione peroxidase and total antioxidant capacity in serum were increased. In addition, the strain no. F8, able to grow in an iron-rich environment, was more effective in alleviating IDA and improving organ indices with fewer side effects compared to ferrous glycinate and ferrous sulfate groups. This study suggests that the iron-rich strain no. F8 may play an important role in improving IDA mice and may be developed as a new iron supplement.

Effect of High Efficiency Digestion and Utilization of Organic Iron Made by Saccharomyces cerevisiae on Antioxidation and Caecum Microflora in Weaned Piglets

Organic iron is expected to replace inorganic iron used in diets as an iron source. Organic iron possesses high absorption efficiency and low fecal iron excretion. This study aims to study the effect of organic iron produced by Saccharomyces cerevisiae (yeast iron) on digestion, utilization, antioxidation and caecum microflora in weaned piglets. In total, 20 piglets that had been weaned after 28 days were divided into 4 groups, each of which followed a different basal diet. The basal diet of each of these 4 groups contained, respectively, 104 mg/kg iron (ferrous sulfate, CON), 84 mg/kg iron (yeast iron, LSC), 104 mg/kg iron (yeast iron, MSC) or 124 mg/kg iron (yeast iron, HSC). This experiment lasted 35 d. The apparent digestibility of iron in LSC, MSC and HMS was higher than that in CON (p < 0.01) and the fecal iron content in LSC, MSC and HMS was lower than that in CON (p < 0.01). Serum iron contents in LSC, MSC and HMS were higher than that in CON (p < 0.01). The iron contents of the heart, lungs, liver, kidney and left gluteus muscle in the MSC and HMS groups were higher than that in CON and LSC (p < 0.05). Serum catalase, glutathione peroxidase, superoxide dismutase activity, superoxide anion, glutathione, hydroxyl free radical scavenging rate, total antioxidant capacity, and liver superoxide anion clearance rate and peroxidase in MSC and HMS were higher than that in CON and LSC (p < 0.05). The contents of nitric oxide and peroxide of the weaned piglets in MSC and HMS were lower than that in CON and LSC (p < 0.05). The abundance of Firmicutes, Blautia and Peptococcus in LSC, HSC and MSC was higher than that in CON (p < 0.01). The abundance of Lactobacillus in CON and LSC was higher than that in MSC and HSC (p < 0.01). The abundance of Acinetobacter, Streptococcus and Prevotella in LSC, MSC and HSC was lower than that in CON (p < 0.01). The results suggested that a diet containing 84 mg/kg iron of yeast iron has the same effect as a diet containing 104 mg/kg iron of ferric sulfate, and that a diet containing 104 or 124 mg/kg iron of yeast iron is superior to a diet containing 104 mg/kg iron of ferric sulfate.

Sterol Composition Modulates the Response of Saccharomyces cerevisiae to Iron Deficiency

Iron is a vital micronutrient that functions as an essential cofactor in multiple biological processes, including oxygen transport, cellular respiration, and metabolic pathways, such as sterol biosynthesis. However, its low bioavailability at physiological pH frequently leads to nutritional iron deficiency. The yeast Saccharomyces cerevisiae is extensively used to study iron and lipid metabolisms, as well as in multiple biotechnological applications. Despite iron being indispensable for yeast ergosterol biosynthesis and growth, little is known about their interconnections. Here, we used lipid composition analyses to determine that changes in the pattern of sterols impair the response to iron deprivation of yeast cells. Yeast mutants defective in ergosterol biosynthesis display defects in the transcriptional activation of the iron-acquisition machinery and growth defects in iron-depleted conditions. The transcriptional activation function of the iron-sensing Aft1 factor is interrupted due to its mislocalization to the vacuole. These data uncover novel links between iron and sterol metabolisms that need to be considered when producing yeast-derived foods or when treating fungal infections with drugs that target the ergosterol biosynthesis pathway.

Preparation and process optimization of microbial organic copper as a feed additive

ABSTRACT As an essential trace element for animals, copper significantly contributes to the growth and health of animals. Compared to inorganic trace elements, organic trace elements are better supplements; notably, they are acquired through microbial transformation. Therefore, we screened for copper-enriched microorganisms from high copper content soil to obtain organic copper. Sodium diethyldithio carbamate trihydrate was applied as a chromogenic agent for determining micro amounts of intracellular copper through spectrophotometry. In total, 50 fungi were isolated after the successful application of the screening platform for copper-rich microbes. Following morphological and molecular biology analyses, the N-2 strain, identified as Aspergillus niger sp. demonstrated showed better copper enrichment potential than others. Notably, the strain tolerance to copper was nearly thrice that of Saccharomyces cerevisiae, up to 1600mg/L. The content of the organic bound copper was 22.84mg Cu/g dry cell. Using the Central Composite Design (CCD) response surface method, we optimized the fermentation condition (inoculation amount, 13%; temperature, 28(C; pH, 5.0). Compared to the original strain results under the single factor fermentation condition, we reported an increase by 24.18% under the optimized conditions. Collectively, these findings provide a reference for uncovering new and low-cost organic copper additives.

The Use of Iron-Enriched Yeast for the Production of Flatbread

The most common cause of iron deficiency is an improperly balanced diet, in which the body’s need for iron cannot be met by absorption of this element from food. Targeted iron supplementation and food fortification may be the main treatments for iron deficiency in the population. However, many iron-rich supplements and foods have low bioavailability of this element. In our study, we used yeast enriched with iron ions to produce flatbread. The yeast cells accumulated iron ions from the medium supplemented with Fe(NO₃)₃·9H₂O, additionally one of the cultures was treated with pulsed electric field in order to increase the accumulation. The potential bioavailability of iron from flatbread containing 385.8 ± 4.12 mg of iron in 100 g dry mass was 10.83 ± 0.94%. All the flatbreads had a moderate glycemic index. There were no significant differences in antioxidant activity against DPPH^• between flatbread with iron-enriched and non-iron-enriched yeast. Sensory evaluation showed that this product is acceptable to consumers since no metallic aftertaste was detected. Iron enriched flatbread can potentially be an alternative to dietary supplements in iron deficiency states.

Expression of a Truncated Yeast Ccc1 Vacuolar Transporter Increases the Accumulation of Endogenous Iron

Iron is an essential micronutrient for all eukaryotic organisms because it participates as a redox cofactor in multiple metabolic processes. Iron bioavailability is highly restricted due to the low solubility of its oxidized form, frequently leading to iron deficiency anemia. The baker’s yeast Saccharomyces cerevisiae is used as a model organism for iron homeostasis studies, but also as a food supplement and fermentative microorganism in the food industry. Yeast cells use the vacuolar Ccc1 transporter to detoxify and store excess iron in the vacuoles. Here, we modulate CCC1 expression and properties to increase iron extraction from the environment. We show that constitutive expression of full-length CCC1 is toxic, whereas deletion of its cytosolic amino-terminal (Nt) domain (NtΔCCC1) rescues this phenotype. Toxicity is exacerbated in cells lacking AFT1 transcription factor. Further characterization of NtΔCcc1 protein suggests that it is a partially functional protein. Western blot analyses indicate that deletion of Ccc1 Nt domain does not significantly alter GFP-Ccc1 protein stability. A functional full-length GFP-Ccc1 protein localized to particular regions of the vacuolar membrane, whereas GFP-NtΔCcc1 protein was evenly distributed throughout this endogenous membrane. Interestingly, expression of NtΔCCC1 increased the accumulation of endogenous iron in cells cultivated under iron-sufficient conditions, a strategy that could be used to extract iron from media that are not rich in iron.

Preparation of S-iron-enriched yeast using siderophores and its effect on iron deficiency anemia in rats

Efforts to obtain organic trace elements have been made, including yeast enrichment and transformation, but the application of yeast for this purpose is restricted by poor tolerance and low enrichment. Siderophores play an important role in iron transport. Thus, the role of siderophores in iron transport under high-iron conditions and the application of siderophores in the enrichment of elements was explored. The results showed that some siderophores from iron-tolerant strains promoted yeast growth and increased its intracellular iron content. Among them, siderophore TZT-12 (from LK1110) was the best for promoting yeast growth and iron conversion. The siderophore-iron-enriched yeast (S-iron-enriched yeast) effectively restored the iron concentration, and an iron concentration of 59.40 mg/g was obtained by adding TZT-12. Iron deficiency anemia in rats was significantly mitigated with S-iron-enriched yeast compared with ferrous sulfate. These findings provide a new perspective on the preparation of organic trace elements for supplementation or food fortification.

Pulsed Electric Field (PEF) Enhances Iron Uptake by the Yeast Saccharomyces cerevisiae

The aim of the study was to investigate the influence of a pulsed electric field (PEF) on the level of iron ion accumulation in Saccharomyces cerevisiae cells and to select PEF conditions optimal for the highest uptake of this element. Iron ions were accumulated most efficiently when their source was iron (III) nitrate. When the following conditions of PEF treatment were used: voltage 1500 V, pulse width 10 μs, treatment time 20 min, and a number of pulses 1200, accumulation of iron ions in the cells from a 20 h-culture reached a maximum value of 48.01 mg/g dry mass. Application of the optimal PEF conditions thus increased iron accumulation in cells by 157% as compared to the sample enriched with iron without PEF. The second derivative of the FTIR spectra of iron-loaded and -unloaded yeast cells allowed us to determine the functional groups which may be involved in metal ion binding. The exposure of cells to PEF treatment only slightly influenced the biomass and cell viability. However, iron-enriched yeast (both with or without PEF) showed lower fermentative activity than a control sample. Thus obtained yeast biomass containing a high amount of incorporated iron may serve as an alternative to pharmacological supplementation in the state of iron deficiency.

Effect of dietary supplementation with yeast Saccharomyces cerevisiae on skin, serum and liver of gilthead seabream (Sparus aurata L)

The effect of dietary supplementation with Saccharomyces cerevisiae on gilthead seabream (Sparus aurata L.) was studied. Four replicates of fish (n = 6) were fed with a commercial diet containing 0 (control, no yeast added) or 10 mg per kilogram of heat-killed (30 min, 60°C) S. cerevisiae. After 4 weeks, half of the fish (two replicates) were injured and continued with the same diet. At 3 and 7 days post-wounding, samples of blood, skin mucus, skin and liver were obtained from each fish. The results showed that calcium concentrations were significantly higher (with respect to control fish) in the serum from fish sampled at 3 days post-wounding, whereas antioxidant enzymes in the skin mucus were altered after wounding (at both 3 and 7 days). Histological analyses revealed oedema, signs of inflammation and white cell recruitment together with a reduction in the epidermis layer in the wounded regions of fish fed control diet. Yeast supplementation did not change growth performance and helped maintain the normal serum calcium concentrations in wounded fish. Furthermore, a reduction in inflammation around wounds in the animals fed yeast with respect to that fed control diet was evident in the histological study. Furthermore, increased levels of stress-related gene expression in liver and skin from wounded fish were obtained. Overall, yeast supplementation seemed to be a functional and appropriate dietary additive to improve skin recovery reducing the stress resulting from wounds.

Molecular strategies to increase yeast iron accumulation and resistance

All eukaryotic organisms rely on iron as an essential micronutrient for life because it participates as a redox-active cofactor in multiple biological processes. However, excess iron can generate reactive oxygen species that damage cellular macromolecules. The low solubility of ferric iron under physiological conditions increases the prevalence of iron deficiency anemia. A common strategy to treat iron deficiency consists of dietary iron supplementation. The baker's yeast Saccharomyces cerevisiae is used as a model eukaryotic organism, but also as a feed supplement. In response to iron deficiency, the yeast Aft1 transcription factor activates cellular iron acquisition. However, when constitutively active, Aft1 inhibits growth probably due to iron toxicity. In this report, we have studied the consequences of using hyperactive AFT1 alleles, including AFT1-1UP, to increase yeast iron accumulation. We first characterized the iron sensitivity of cells expressing different constitutively active AFT1 alleles. We rescued the high iron sensitivity conferred by the AFT1 alleles by deleting the sphingolipid signaling kinase YPK1. We observed that the deletion of YPK1 exerts different effects on iron accumulation depending on the AFT1 allele and the environmental iron. Moreover, we determined that the impairment of the high-affinity iron transport system partially rescues the high iron toxicity of AFT1-1UP-expressing cells. Finally, we observed that AFT1-1UP inhibits oxygen consumption through activation of the RNA-binding protein Cth2. Deletion of CTH2 partially rescues the AFT1-1UP negative respiratory effect. Collectively, these results contribute to understand how the Aft1 transcription factor functions and the multiple consequences derived from its constitutive activation.

Iron-rich microorganism-enabled synthesis of magnetic biocarbon for efficient adsorption of diclofenac from aqueous solution

Microorganisms in nature have been suggested as effective synthetic platform for functional materials construction. In this study, we cultured a typical white rot fungus of Phanerochaete chrysosporium in iron-containing medium to obtain iron-rich biomass, serving as sole precursor for magnetic biocarbon synthesis. The accumulated iron in biomass reached to 4.6 wt%. After carbonization and activation, microporous magnetic biocarbon (Fe/BC) with high specific surface area of 1986 m² g^-1 was obtained. When applied as adsorbent for a model pharmaceutical (diclofenac sodium, DCF) removal from aqueous solution, a high adsorption capacity of 361.25 mg g^-1 was found for the developed Fe/BC. Systematic isotherm, kinetic, thermodynamic and recycle studies were conducted to investigate adsorption behaviors of DCF onto Fe/BC. This work not only provides a novel strategy for magnetic biocarbon construction, but also envisions new perspective on the utilization of a variety of microorganisms in nature for functional materials preparation.

Production of antioxidant and ACE-inhibitory peptides from Kluyveromyces marxianus protein hydrolysates: Purification and molecular docking

Kluyveromyces marxianus protein hydrolysates were prepared by two different sonicated-enzymatic (trypsin and chymotrypsin) hydrolysis treatments to obtain antioxidant and ACE-inhibitory peptides. Trypsin and chymotrypsin hydrolysates obtained by 5 h, exhibited the highest antioxidant and ACE-inhibitory activities. After fractionation using ultra-filtration and reverse phase high performance liquid chromatography (RP-HPLC) techniques, two new peptides were identified. One fragment (LL-9, MW = 1180 Da) with the amino acid sequence of Leu-Pro-Glu-Ser-Val-His-Leu-Asp-Lys showed significant ACE inhibitory activity (IC₅₀ = 22.88 μM) while another peptide fragment (VL-9, MW = 1118 Da) with the amino acid sequence of Val-Leu-Ser-Thr-Ser-Phe-Pro-Pro-Lys showed the highest antioxidant and ACE inhibitory properties (IC₅₀ = 15.20 μM, 5568 μM TE/mg protein). The molecular docking studies revealed that the ACE inhibitory activities of VL-9 is due to interaction with the S2 (His513, His353, Glu281) and S’1 (Glu162) pockets of ACE and LL-9 can fit perfectly into the S1 (Thr345) and S2 (Tyr520, Lys511, Gln281) pockets of ACE.

INVESTIGATION OF THE INFLUENCE OF NANOPARTICLES OF METALS ON FERMENTTATION OF WORT OF HIGH CONCENTRATIONS

There was theoretically grounded and experimentally proved the expedience of enriching high-concentrated wort of the starch-containing raw material with such additional source of mineral nutrition for yeast cells as nanoparticles of metals. There was studied the influence of nanoparticles of metals on hydrolysis of biopolymers of the raw material and biosynthesis of organic compounds at wort fermentation. It was experimentally established, that the most positive influence of biosynthetic properties of yeast cells is realized by zinc and magnesium. At using zinc and magnesium, yeast biomass and alcohol content in mashes increase. Best chemical-technological indices of mashes were received at adding nanoparticles of zinc and magnesium at the stage of batch dilution. There was experimentally studied the synthesis of volatile organic admixtures in marsh distillates depending on point of adding nanoparticles of metals.

Protein Hydrolysates as Promoters of Non-Haem Iron Absorption

Iron (Fe) is an essential micronutrient for human growth and health. Organic iron is an excellent iron supplement due to its bioavailability. Both amino acids and peptides improve iron bioavailability and absorption and are therefore valuable components of iron supplements. This review focuses on protein hydrolysates as potential promoters of iron absorption. The ability of protein hydrolysates to chelate iron is thought to be a key attribute for the promotion of iron absorption. Iron-chelatable protein hydrolysates are categorized by their absorption forms: amino acids, di- and tri-peptides and polypeptides. Their structural characteristics, including their size and amino acid sequence, as well as the presence of special amino acids, influence their iron chelation abilities and bioavailabilities. Protein hydrolysates promote iron absorption by keeping iron soluble, reducing ferric iron to ferrous iron, and promoting transport across cell membranes into the gut. We also discuss the use and relative merits of protein hydrolysates as iron supplements.

Soybean Ferritin Expression in Saccharomyces cerevisiae Modulates Iron Accumulation and Resistance to Elevated Iron Concentrations

Fungi, including the yeast Saccharomyces cerevisiae, lack ferritin and use vacuoles as iron storage organelles. This work explored how plant ferritin expression influenced baker's yeast iron metabolism. Soybean seed ferritin H1 (SFerH1) and SFerH2 genes were cloned and expressed in yeast cells. Both soybean ferritins assembled as multimeric complexes, which bound yeast intracellular iron in vivo and, consequently, induced the activation of the genes expressed during iron scarcity. Soybean ferritin protected yeast cells that lacked the Ccc1 vacuolar iron detoxification transporter from toxic iron levels by reducing cellular oxidation, thus allowing growth at high iron concentrations. Interestingly, when simultaneously expressed in ccc1Δ cells, SFerH1 and SFerH2 assembled as heteropolymers, which further increased iron resistance and reduced the oxidative stress produced by excess iron compared to ferritin homopolymer complexes. Finally, soybean ferritin expression led to increased iron accumulation in both wild-type and ccc1Δ yeast cells at certain environmental iron concentrations.

IMPORTANCE

Iron deficiency is a worldwide nutritional disorder to which women and children are especially vulnerable. A common strategy to combat iron deficiency consists of dietary supplementation with inorganic iron salts, whose bioavailability is very low. Iron-enriched yeasts and cereals are alternative strategies to diminish iron deficiency. Animals and plants possess large ferritin complexes that accumulate, detoxify, or buffer excess cellular iron. However, the yeast Saccharomyces cerevisiae lacks ferritin and uses vacuoles as iron storage organelles. Here, we explored how soybean ferritin expression influenced yeast iron metabolism, confirming that yeasts that express soybean seed ferritin could be explored as a novel strategy to increase dietary iron absorption.

Responses of Saccharomyces cerevisiae Strains from Different Origins to Elevated Iron Concentrations

Iron is an essential micronutrient for all eukaryotic organisms. However, the low solubility of ferric iron has tremendously increased the prevalence of iron deficiency anemia, especially in women and children, with dramatic consequences. Baker's yeast Saccharomyces cerevisiae is used as a model eukaryotic organism, a fermentative microorganism, and a feed supplement. In this report, we explore the genetic diversity of 123 wild and domestic strains of S. cerevisiae isolated from different geographical origins and sources to characterize how yeast cells respond to elevated iron concentrations in the environment. By using two different forms of iron, we selected and characterized both iron-sensitive and iron-resistant yeast strains. We observed that when the iron concentration in the medium increases, iron-sensitive strains accumulate iron more rapidly than iron-resistant isolates. We observed that, consistent with excess iron leading to oxidative stress, the redox state of iron-sensitive strains was more oxidized than that of iron-resistant strains. Growth assays in the presence of different oxidative reagents ruled out that this phenotype was due to alterations in the general oxidative stress protection machinery. It was noteworthy that iron-resistant strains were more sensitive to iron deficiency conditions than iron-sensitive strains, which suggests that adaptation to either high or low iron is detrimental for the opposite condition. An initial gene expression analysis suggested that alterations in iron homeostasis genes could contribute to the different responses of distant iron-sensitive and iron-resistant yeast strains to elevated environmental iron levels.

Effects of Fe-YM1504 on iron deficiency anemia in rats

Iron deficiency anemia (IDA) is one of the most serious forms of malnutrition.

Preparation of iron-enriched baker's yeast and its efficiency in recovery of rats from dietary iron deficiency

OBJECTIVES

Iron is an important mineral, essential for the health and function of mammalian cells. Despite its key role, iron deficiency in humans is common worldwide, often leading to significant health issues within the population. The aim of this study was to evaluate the potential of using iron-enriched baker's yeast as a source of iron, especially for the protection and recovery from conditions related to anemia.

METHODS

Iron-enriched yeast was prepared by cultivating cells on basal medium comprising different iron concentrations. The effects of iron supplementation on animal health were assessed by feeding anemic rats with a variety of diets containing either inorganic iron or iron-enriched yeast. Body weight, iron bioavailability, blood parameters, and the activity of iron-containing enzymes (catalase) were studied.

RESULTS

Iron accumulation in yeast cells increased with iron concentration, reaching a maximum of 15 mg/g when 32 mM iron was applied. Rat groups fed iron-enriched yeast had the highest feed efficiency, iron bioavailability, and hemoglobin concentration. The source of iron supplementation influenced catalase activity in kidney tissues, increasing from 70 U/g tissue in anemic rats to 90 U/g tissue (inorganic iron salt), 110 U/g tissue (inorganic iron salt and non-enriched dry yeast), 145 U/g tissue (iron-enriched yeast 15 mg/g iron) and 115 U/g tissue (iron-enriched yeast 30 mg/g iron). The histologic study of tissues from liver, kidney, heart, and spleen of rats from different groups showed that the damage observed in tissues of anemic rats, was not observed after feeding with iron-enriched yeasts.

CONCLUSION

The results demonstrated that ingestion of iron-enriched yeast is more efficient than inorganic treatment in recovery from iron deficiency, including tissue recovery in rats.

Mineral composition of the sugarcane juice and its influence on the ethanol fermentation

In the present work, we evaluated the mineral composition of three sugarcane varieties from different areas in northeast Brazil and their influence on the fermentation performance of Saccharomyces cerevisiae. The mineral composition was homogeneous in the different areas investigated. However, large variation coefficients were observed for concentrations of copper, magnesium, zinc and phosphorus. Regarding the fermentation performances, the sugarcane juices with the highest magnesium concentration showed the highest ethanol yield. Synthetic media supplemented with magnesium also showed the highest yield (0.45 g g(-1)) while the excess of copper led to the lowest yield (0.35 g g(-1)). According to our results, the magnesium is the principal responsible for the increase on the ethanol yield, and it also seems to be able to disguise the inhibitory effects of the toxic minerals present in the sugarcane juice.

The uptake of different iron salts by the yeast Saccharomyces cerevisiae

Yeasts can be enriched with microelements, including iron; however, special physicochemical conditions are required to formulate a culture media that promotes both yeast growth and iron uptake. Different iron sources do not affect biomass formation; however, considering efficacy, cost, stability, and compatibility with Saccharomyces cerevisiae metabolism, ferrous sulphate is recommended.

Characterization of Saccharomyces cerevisiae promoters for heterologous gene expression in Kluyveromyces marxianus

Kluyveromyces marxianus is now considered one of the best choices of option for industrial applications of yeast because the strain is able to grow at high temperature, utilizes various carbon sources, and grows fast. However, the use of K. marxianus as a host for industrial applications is still limited. This limitation is largely due to a lack of knowledge on the characteristics of the promoters since the time and amount of protein expression is strongly dependent on the promoter employed. In this study, four well-known constitutive promoters (P(CYC), P(TEF), P(GPD), and P(ADH)) of Saccharomyces cerevisiae were characterized in K. marxianus in terms of protein expression level and their stochastic behavior. After constructing five URA3-auxotrophic K. marxianus strains and a plasmid vector, four cassettes each comprising one of the promoters--the gene for the green fluorescence protein (GFP)--CYC1 terminator (T(CYC)) were inserted into the vector. GFP expression under the control of each one of the promoters was analyzed by reverse transcription PCR, fluorescence microscopy, and flow cytometer. Using these combined methods, the promoter strength was determined to be in the order of P(GPD) > P(ADH) ∼ P(TEF) >> P(CYC). All promoters except for the P(CYC) exhibited three distinctive populations, including non-expressing cells, weakly expressing cells, and strongly expressing cells. The relative ratios between populations were strongly dependent on the promoter and culture time. Forward scattering was independent of GFP fluorescence intensity, indicating that the different fluorescence intensities were not just due to different cell sizes derived from budding. It also excluded the possibility that the non-expressing cells resulted from plasmid loss because plasmid stability was maintained at almost 100 % over the culture time. The same cassettes, cloned into a single copy plasmid pRS416 and transformed into S. cerevisiae, showed only one population. When the cassettes were integrated into the chromosome, the stochastic behavior was markedly reduced. These combined results imply that the gene expression stochasticity should be overcome in order to use this strain for delicate metabolic engineering, which would require the co-expression of several genes.