Effect of cultivation conditions on the cytochrome system of Candida mycoderma yeasts

The effect of aeration of the medium, the source of carbon, yeast autolysate and its components (amino acids, vitamins, cytochrome precursors) on the biosynthesis of cytochromes and the ratio between them was studied in the cells of Candida mycoderma. The content of cytochromes b and c increased in the cells at the stationary phase of growth on the Rieder medium regardless of the carbon source and in the presence of elevated concentrations of iron and yeast autolysate (or one of its components, delta-aminolevulinic acid), whereas the content of cytochromes a + a3 decreased. These changes in the content of cytochromes were found in the conditions of strong oxygen deficiency in the medium during the stationary phase.     

Reduction of Nucleic Acid Content in Candida Yeast Cells by Bovine Pancreatic Ribonuclease A Treatment

Yeast as a source of protein for human consumption is limited by its relatively high nucleic acid content. In this study, we developed an enzymatic method of decreasing the nucleic acid content. Candida utilis cells, heat-shocked at 80 C for 30 sec, were treated with bovine pancreatic ribonuclease A. Maximum leakage of nucleic acid was observed when the incubation temperature was between 55 and 65 C, the pH of the system from 6.75 to 8.0, and the enzyme-to-cell ratio 1:10,000 on a weight-by-weight basis. Other factors, such as yeast strain, age of cells, and method of propagation, did not influence the susceptibility of the yeast cells to the action of ribonuclease. Buffers and monovalent cations had no inhibiting effects. Magnesium and calcium ions at concentrations greater than 0.001 m showed marked inhibition on the rate of nucleic acid leakage. This enzymatic method reduced the nucleic acid content of yeast cells from 7.5 to 9.0% to 1.5 to 2.0% with no significant concomitant loss of protein.     

Study of Candida ingens grown on the supernatant derived from the anaerobic fermentation of monogastric animal wastes.

A pellicle-forming yeast, identified as Candida ingens, was found to grow on substrates derived from the anerobic fermentation of monogastric animal wastes. The organism used volatile fatty acids C2 to C6 and ammonia nitrogen. It had a preferential uptake of the acids in increasing order of molecular weight, removing 90% of the total titratable volatile acid. The nonwrinkled pellicle had a doubling time of 3.2 h, and the doubling time of the wrinkled pellicle was 4.2 h. Proximate amino acid and nucleic acid analyses suggested that the organism might be acceptable as a source of single cell protein. Its vitamin B group content compared favorably with that of other yeasts. It contained 6% calcium and 7% phosphorus. It could be useful in removing these minerals from effluents as well as in providing them as nutrients in livestock rations.     

RNA removal from Candida utilis by chemical and thermal treatments

The removal of the content of nucleic acids of fodder yeast (Candida utilis) by treatment with HCl or heat shock was investigated Acid concentrations between 5 and 15% (on dried matter basis) were used. A maximal removal of the content of nucleic acids of 88% was realized wheńn was worked with 15% HCl, 90 °C during 30 minutes. But under this conditions were observed high demanges of protein and also of some essential amino acids Good results for diminishing the content of nucleic acids were reached with the highest concentration of acid and a treatment during 20 minutes The experiments with heat shock were carried out at 68 °C, different times for heating and different contents of yeast In this way better results than for treatment with acid according to diminishing the content of nucleic acids and yield of protein and essential amino acids were reached A removal of over 80% of the content of nucleic acids was achieved in all cases.     

EFFECTS OF CERTAIN LIMITING CONDITIONS ON THE SYNTHESIS OF B VITAMINS BY YEAST

In yeast crops which were grown in the presence of various inhibitors, there was considerable variation in content of the various B vitamins. A higher degree of parallelism in variation in content was found to exist between thiamine and niacin than between any other pair of vitamins; this has been interpreted as indicating that the predominant functions of these two vitamins are their established rôles in fermentation. Values for inositol indicate that it may be involved in fermentation processes, but this is not the case for other members of the B complex. Biotin appears to be unique since in no case did the biotin content of yeast grown in the presence of an inhibitor fall below that of the control yeast. There was some evidence of synthesis of biotin, or a material with biotin activity, in the presence of certain inhibitors, the most striking instance being with sulfaguanidine. An exogenous supply of biotin was essential for extensive proliferation of F. B. yeast, and yeast grown in a medium to which biotin was the only added vitamin contained the B vitamins in amounts very similar to those found in the control yeast, the most marked differences being in increased vitamin B₆ and p-aminobenzoic acid contents. In the absence of biotin, significant amounts of all of the B vitamins except biotin were synthesized, both in the presence and absence of certain other members of the B complex. The addition of thiamine, pyridoxine, inositol, and β-alanine to the culture medium caused a reduction in the amounts of vitamin B₆ and p-aminobenzoic acid synthesized. F. B. yeast was able to grow in a xylose medium only when certain of the B vitamins were present, and even then growth was limited. Evidence was obtained for some synthesis of all of the vitamins investigated except biotin and vitamin B₆. The most significant differences in vitamin content between galac yeast and the parent F. B. strain were in folic acid and vitamin B₆, the former being considerably reduced in amount, the latter being increased.     

氨基酸对白念珠菌形态学影响的研究

目的初步探讨单个氨基酸对白念珠菌形态学的影响。方法用0．67％的酵母氮源基础培养基和2％葡萄糖配制成SD合成培养基,37％恒温摇床培养,研究单个天然氨基酸对白念珠菌形态学的影响,并分别通过不添加碳源和厌氧条件下培养观察对精氨酸诱导的菌丝的影响。结果在含10mmol／L的L－精氨酸的SD液体培养基中,可见大量的菌丝。在含10mmol／L的L一半胱氨酸、L．苏氨酸、L－缬氨酸和L－色氨酸的sD液体培养基中,可见典型的酵母细胞,未见菌丝。在含10mmol／L的其他单个氨基酸的SD液体培养基中可见混合的酵母和菌丝结构。在不含氨基酸或含各种天然氨基酸的SD固体培养基上,白念珠菌的菌落均光滑。但在含10mmol／L的L-精氨酸固体培养基上,光滑的菌落周围可见小的突起,镜下可见菌丝。无氧条件下,无论有无碳源,含精氨酸的SD培养液中白念珠菌只能形成酵母细胞,生长部分受到抑制。结论精氨酸可以诱导白念珠菌菌丝形成,厌氧条件下精氨酸不能诱导白念珠菌菌丝形成。     

Variety of effects of vitamins on yeast cells in aerobic conditions]

The effect of thiamine and biotin on the processes of cell division, assimilation of glucose, and accumulation of the biomass and nitrogen in the cells was studied with the Candida yeast. The action of the vitamins depended on the source of nitrogen. In some strains, asparagine can substitute for biotin. Biotin has different effect on the production of gamma-aminobutyric acid in Candida pulcherrima, C. guilliermondii. C. tropicalis K3-10. High concentrations of arginine were found in C. guilliermondii var. membranaefaciens in the presence of biotin. The vitamins did not favour the assimilation of nitrate nitrogen in species which were not adapted to this source of nitrogen.     

Joint effect of nitrogen sources and B vitamin supplementation of date juice on lactic acid production by Lactobacillus casei subsp. rhamnosus

The use of date juice as a substrate for lactic acid production was investigated. Various nitrogen sources were compared with yeast extract for efficient lactic acid production by Lactobacillus casei subsp. rhamnosus. Among different nitrogen sources added to date juice (yeast extract, ammonium sulfate, tryptic soy, urea, peptone, and casein hydrolysate), yeast extract was the most efficient. The effect of yeast extract could have been due to its B vitamin content. The addition of five B vitamins at less than 25 mg/l to date juice with any nitrogen source enhanced lactic acid production to some extent, except for date juice with yeast extract or urea or peptone. The most significant increase was obtained with ammonium sulfate. Half of the yeast extract content (10 g/l) in a supplemented date juice could be replaced by a mixture of B vitamins at less than 25 mg/l, and ammonium sulfate at 2.6 g/l with no significant decrease in lactic acid production.     

Cultivation of the yeast Mycoderma vini on an ethanol-containing medium and evaluation of the nutritive value of isolated yeast proteins]

A stable process of the development of the yeast Mycoderma vini is possible during continuous cultivation on the nutrient medium containing 3% ethanol as the only carbon and energy source. The maximum coefficient of ethanol consumption is 65%. The total protein isolated from the yeast biomass is similar to casein in terms of the composition and susceptibility to gastrointestinal enzymes in vitro. This protein shows a low content of nucleic acids.     

Isolation and Characterization of a Thermotolerant Methanol-Utilizing Yeast

A yeast capable of growth on methanol as its sole carbon-energy source was isoalted from soil samples and identified as a strain of Hansenula polymorpha. A continuous enrichment culture at 37 C with a simple mineral salts medium was used to select this organism. The isolate, designated DL-1, has a maximal specific growth rate of 0.22 per h, at pH 4.5 to 5.5 and temperatures of 37 to 42 C, in simple mineral salts medium with methanol (0.5%), biotin, and thiamine. Growth occurred in a chemostat at temperatures up to 50 C, with strong growth at 45 C. The maximal growth yield of the yeast on methanol was 0.36 g of dry cell weight per g of methanol, and the yield on oxygen was 0.37 g of dry cell weight per g of O(2). Protein content of the isolate is 46%, and total nucleic acid content varies from 5.0 to 7.0% with increasing growth rate from 0.08 to 0.20 per h. The amino acid profile of this yeast protein indicates that it could serve as a good source of food protein. Feeding studies with rats show the yeast to have no toxic effects.     

Control of fatty-acid synthetase levels by exogeneous long-chain fatty acids in the yeasts Candida lipolytica and Saccharomyces cerevisiae.

Endogeneous fatty acid biosynthesis in the two yeast species, Saccharomyces cerevisiae and Candida lipolytica is completely repressed by the addition of long-chain fatty acids to the growth medium. In Candida lipolytica, this repression is accompanied by a corresponding loss of fatty acid synthetase activity in the cell homogenate, when the cells were grown on fatty acids as the sole carbon source. The activity of the Saccharomyces cerevisiae fatty acid synthetase, however, remains unaffected by the addition of fatty acids to a glucose-containing growth medium. From fatty-acid-grown Candida lipolytica cells no fatty acid synthetase complex can be isolated, nor is there any immunologically cross-reacting fatty acid synthetase protein detectable in the crude cell extract. From this it is concluded that Candida lipolytica, but not Saccharomyces cerevisiae, is able to adapt to the growth on fatty acids either by repression of fatty acid synthetase biosynthesis or by a fatty-acid-induced proteolytic degradation of the multienzyme complex. Similarly, the fatty acid synthetase complex disappears rapidly from stationary phase Candida lipolytica cells even after growth in fatty-acid-free medium. Finally, it was found that the fatty acid synthetase complexes from Saccharomyces cerevisiae and Candida lipolytica, though very similar in size and subunit composition, were immunologically different and had no common antigenic determinants.     

Production of aflatoxin by an Aspergillus flavus isolate cultured under a limited oxygen supply.

In a previous experiment on the preservation of hay of high moisture content with formic acid, among other agents, aflatoxin was formed in the hay, and aflatoxin-forming strains of Aspergillus flavus were isolated from this hay after incubation in air as well as in an anaerobic jar. One isolate from the anaerobic jar was cultivated in a chemostat (Bioflo model C 30; New Brunswick Scientific Co.) in a defined medium with added B vitamins, yeast extract, or formic acid, with or without gas flow (air or nitrogen). In all cases where spore germination occurred, aflatoxin was formed in the cultures with gas flow, and small quantities of aflatoxins B1 and B2 occurred even in an atmosphere of nitrogen. Addition of B vitamins and supply of traces of air gave an approximately 15-fold increase in the amount of aflatoxin in 2 days. Carbon dioxide enrichment hindered aflatoxin formation on the defined medium even in the presence of B vitamins, but when formic acid was added, small quantities (5 to 15 micrograms/liter) were formed, and this low level remained constant until the gas flow was started.     

Production of aflatoxin by an Aspergillus flavus isolate cultured under a limited oxygen supply

In a previous experiment on the preservation of hay of high moisture content with formic acid, among other agents, aflatoxin was formed in the hay, and aflatoxin-forming strains of Aspergillus flavus were isolated from this hay after incubation in air as well as in an anaerobic jar. One isolate from the anaerobic jar was cultivated in a chemostat (Bioflo model C 30; New Brunswick Scientific Co.) in a defined medium with added B vitamins, yeast extract, or formic acid, with or without gas flow (air or nitrogen). In all cases where spore germination occurred, aflatoxin was formed in the cultures with gas flow, and small quantities of aflatoxins B1 and B2 occurred even in an atmosphere of nitrogen. Addition of B vitamins and supply of traces of air gave an approximately 15-fold increase in the amount of aflatoxin in 2 days. Carbon dioxide enrichment hindered aflatoxin formation on the defined medium even in the presence of B vitamins, but when formic acid was added, small quantities (5 to 15 micrograms/liter) were formed, and this low level remained constant until the gas flow was started.     

Physiological and nutritional features of Corynebacterium pyogenes

Growth and acid metabolic products were similar when Corynebacterium pyogenes was grown aerobically or anaerobically in a serum-free medium (SFM). This indicated that C. pyogenes obtains energy for growth primarily by fermentative metabolism even under aerobic growth conditions. Growth yield was reduced by 90% in SFM minus glucose, 50% in SFM minus NaHCO3, 90% in SFM minus yeast extract, 100% in SFM minus Trypticase and yeast extract, and 30% in SFM minus haemin or Trypticase. Growth was not detectable when a known mixture of amino acids, vitamins, and nucleic acid bases were substituted for Trypticase and yeast extract in SFM; addition to the latter medium of a peptide source such as Trypticase or casitone supported good growth of the organism. When NaHCO3 was omitted from SFM and dissolved CO2 in the medium was rigorously excluded, growth was undetectable indicating that C. pyogenes has an obligate requirement for CO2 for growth. Succinate, formate and acetate were the major fermentation products in SFM, whereas in SFM minus HCO-3 or haemin, lactate was the major product and only small quantities of other acids accumulated.     

Simple Process for the Reduction in the Nucleic Acid Content in Yeast

A simple one-step process for the nucleic acid reduction in Rhodotorula glutinis is described. The process consists of submitting the yeast cells to a heat treatment in an acidic (pH 2) spent medium. The optimal temperature for pH 2 medium is 90 C and the final nucleic acid content in treated yeasts was 1.2%. Heat treatment at acidic pH is preferred to that at alkaline pH because it offers a better protection for amino acids and crude protein, while being more efficient in lowering the nucleic acid level. The new process is economic and rapid and could be easily used for industrial application.     

Reduction of the nucleic acid content of single-cell protein concentrates

Methods for reducing the content of nucleic acid in protein concentrates from disintegrated yeast and microalgae were investigated. Protein concentrates were prepared by acid precipitation of extracted protein after cell wall separation. The influence of alkaline protein extraction on the content of RNA in isoelectrically precipitated protein concentrates was studied. It was found that when a strong decrease in the RNA content was obtained, this was followed by a decrease in the yield of protein concentrate. Protein concentrates were also prepared without cell wall separation by precipitation with different agents after cell disintegration. In the precipitates from microalgae, a RNA reduction was obtained. Precipitation of yeast, protein gave no essential reduction with the precipitants used. Precipitation of yeast protein by heating at an alkaline pH gave a protein concentrate with a low content of RNA. A slightly lower RNA content was obtained when the precipitation was performed in the presence of NaCl. The yield of amino acid nitrogen was 70–80% and the RNA content was 1–2%. A process with precipitation at alkaline pH for the production of microbial protein concentrates with a low content of nucleic acid is suggested.     

Changes in the composition of intracellular lipids and hydrocarbons in Candida tropicalis in the absence of growth]

The fatty acid composition of lipids and the composition of hydrocarbons were studied in Candida tropicalis cultivated on a medium with propionic acid and incubated in the conditions of starvation and on a medium containing glucose-1-6-14C but no nitrogen. Intracellular fatty acids with an odd number of carbon atoms were found to be easily metabolized by yeast cells. The content and composition of intracellular hydrocarbons were very labile and underwent intensive transformation caused by changes in the metabolism of the yeast cell.     

Composition of Methanospirillum hungatii GP1 during growth on different media

Growth of Methanospirillum hungatii GP1 as determined by optical density measurement wsa comparable to growth assessed by cell dry weight, ribonucleic acid content, and deoxyribonucleic acid content. Cultivation of M. hungatii on synthetic medium containing mineral salts, vitamins, and acetic acid indicated that, on a dry weight basis, cell constituents such as protein (71%), ribonucleic acid (15.8%), deoxyribonucleic acid (1.6%), and total carbohydrate (3.2%) did not vary significantly with the growth phase. Cells grown in the synthetic medium supplemented with yeast extract and tryptone had slightly higher protein content (76%), but the concentrations of the other cell constituents were similar and did not fluctuate much during growth. Nitrogen limiting growth resulted in somewhat lower ribonucleic acid content as well as slightly higher protein content than that in cells grown in nonlimiting medium. Methanospirillum hungatii did not accumulate any of the commonly known reserve materials under nitrogen or carbon and hydrogen limiting growth.     

Mitochondrial function and toxicity: role of B vitamins on the one-carbon transfer pathways

The B vitamins are water-soluble vitamins that are required as coenzymes for reactions essential for cellular function. This review focuses on the essential role of vitamins in maintaining the one-carbon transfer cycles. Folate and choline are believed to be central methyl donors required for mitochondrial protein and nucleic acid synthesis through their active forms, 5-methyltetrahydrofolate and betaine, respectively. Cobalamin (B12) may assist methyltetrahydrofolate in the synthesis of methionine, a cysteine source for glutathione biosynthesis. Pyridoxal, pyridoxine and pyridoxamine (B6) seem to be involved in the regeneration of tetrahydrofolate into the active methyl-bearing form and in glutathione biosynthesis from homocysteine. Other roles of these vitamins that are relevant to mitochondrial functions will also be discussed. However these roles for B vitamins in cell function are mostly theoretically based and still require verification at the cellular level. For instance it is still not known what B vitamins are depleted by xenobiotic toxins or which cellular targets, metabolic pathways or molecular toxic mechanisms are prevented by B vitamins. This review covers the current state of knowledge and suggests where this research field is heading so as to better understand the role vitamin Bs play in cellular function and intermediary metabolism as well as molecular, cellular and clinical consequences of vitamin deficiency. The current experimental and clinical evidence that supplementation alleviates deficiency symptoms as well as the effectiveness of vitamins as antioxidants will also be reviewed.     

Ability of casamino acids to support gellan production by Sphingomonas paucimobilis ATCC 31461

The ability of casamino acids and vitamin-assay casamino acids to support gellan production by Sphingomonas paucimobilis ATCC 31461 was examined in a medium containing glucose or corn syrup as the carbon source relative to yeast extract supplementation. When glucose or corn syrup served as the carbon source, the presence of yeast extract in the growth medium stimulated gellan production by strain ATCC 31461 on casamino acids. Using vitamin-assay casamino acids as the nitrogen source, the addition of vitamins lowered gellan synthesis by glucose-grown cells regardless of yeast extract supplementation while gellan elaboration by corn syrup-grown strain ATCC 31461 cells could only be increased by supplementing vitamins into medium lacking yeast extract. Independent of carbon source, the absence of yeast extract in the medium reduced biomass production. Biomass production by the strain grown on either carbon source was increased by supplementing vitamins in the medium containing yeast extract.