Yeasts are genesCloning experimentCommonly used inEukaryoteReceptor cell, culture yeast and cultureEscherichia coliSame convenience.yeastCloning vectorThere are also many kinds.Yeasts also have plasmids, which are 2 μ m long and about 6300 bp.This plasmid exists at least for a period of time innucleusIn addition to the inner chromosome, the 2 μ m plasmid and the plasmid in Escherichia coli can be used to construct aShuttle plasmid。Yeast clone vectors are constructed on this basis.[1]
Yeast is a single celled fungus, notSystem evolutionClassified unit.A kind of tiny invisible to the naked eyeUnicellular microorganism, can ferment sugar into alcohol andcarbon dioxide, distributed throughout the nature, is a typical heterotrophicFacultative anaerobeIt can survive under both aerobic and anaerobic conditions. It is a naturalStarter。
Generally, it refers to all kinds of single-cell fungi that can ferment sugars, which can be used for brewing orpathogenic bacteria——genetic engineeringandcell cycleStudiedModel organism。Yeast is the earliest microorganism used in the history of human civilization.There are more than 1000 yeasts known. According to the yeast producing spores（AscosporeandBasidiospore）Yeasts can be divided into three categories: spore forming strains belong toAscomycetesandBasidiomycetes。No spore formation, but mainly throughBudding reproductionThose who come to breed are called noComplete fungi, or "false yeast" (yeast like).
Few yeasts are known to be classified intoAscomycetes。Yeasts are widely distributed in nature, mainly growing in acidic, wet and sugary environment.In February 2018, the precise customized synthesis of yeast long chromosomes was awarded the Ministry of Science and TechnologyTop Ten Scientific Progress in China in 2017。[2]
[Definition] Fermentation: the decomposition of organic matter due to certain bacteria or enzymes is called "fermentation".The fungus that can ferment organic matter is called "yeast".Also called "yeast" or "brewer's yeast".
Yeast is a kind of single-cell fungus, which can survive in both aerobic and anaerobic environments. It belongs toFacultative anaerobe。
Cell morphology
Yeast cell width (diameter) is about 2~6μmThe length is 5~30 μ m, and some are longer. The individual forms are sphericalOval, elliptical, columnar, andsausageAnd so on.
Most yeast can be separated from the environment rich in sugar, such as some fruits（Grape、Apple, peach, etc.) or plant secretions (such ascactusJuice).Some yeastinsectInternal life.Yeast is a single celled eukaryotic microorganism, which usually has spherical, ovalSausageShape, oval, lemon shaped or lotus root shaped, which is much larger than the single cell individual of bacteria, generally 1~5 or 5~20 microns.Yeast has no flagella and cannot swim.Yeast has typicalEukaryotic cellStructure, withcell wall, cell membrane, nucleuscytoplasm、vacuole、mitochondrionSome also haveMicrobody。
The colony characteristics of most yeasts are similar to those of bacteria, butBacterial colonyLarge and thick, the surface of the colony is smooth, moist, viscous, easy to pick up, the colony texture is uniform, and the color of the front and back, the edge, and the center is very uniform,colony of bacteriaMost are milky white, a few are red, and some are black.
BuddingThis is the main way for yeast to reproduce asexually.Mature yeast cells first grow a small bud, the bud cells grow to a certain extentmother cellsContinue to grow, and then form new individuals.There are buds at one end, two ends, three ends and multiple ends.
Characteristics: The vegetative cells are haploid;Asexual reproductionwithSchizogenesisMode;Diploid cells cannot live independently, because the diploid stage is short, once generatedMeiosis。
Characteristics: The vegetative body is diploid, and it is constantly budding. The vegetative stage of diploid body is long, and the haploid ascospores join in the ascus.Haploid stage only exists in the form of ascospores, so it cannot live independently.
Constituent sequence
staySaccharomyces cerevisiaeBefore the start of the sequencing program, people have identified the coding in yeast through traditional genetic methodsRNAorproteinAbout 2600 genes.Through the integrity of Saccharomyces cerevisiaegenomeSequencing found that there were 5885 codes in the 12068kb genome sequenceSpecificityProteousOpen reading box。This means that there is one protein coding gene every 2 kb in the yeast genome, that is, 72% of the whole genomeNucleotide sequenceIt consists of an open reading box.This indicates that yeast gene is higher than othersEukaryoteGene arrangementclose together.For example, in the genome of nematode, there is one protein coding gene every 6 kb on average;stayhuman genomeMedium, every 30kb or moreBaseTo find a gene that encodes proteins.The tightness of yeast genome is due to genesBay areaShort and mediumIntronRare.Open reading frame of yeast genomeAverage length1450bp, i.e. 483CodonThe longest is an open reading frame (4910 codons) with unknown function on chromosome XII, and there are a few open reading frames with a length of more than 1500 codons.In the yeast genome, there are also genes encoding short proteins, for example, 40amino acidConstituentCell plasma membraneProteolipidPMP1 gene.In addition, the yeast genome also contains: about 140 genes encoding RNA, arranged at the long end of chromosome XII;40 codesSnRNAThe gene of, dispersed in 16 chromosomes;275 belonging to 43 familiestRNAGenes are also widely distributed ingenomeMedium.[3]
SequencingRevealed yeastgenomeMedium to large scaleBase compositionChange.Most yeast chromosomes are composed ofGCrichDNA sequenceAnd GC lack DNA sequence mosaic composition.suchGC contentThe relationship between chromosome structure, gene density andRecombination frequencyofAreas with high GC content are generally located inChromosome armThe gene density of these regions is higher in the middle of the;Areas with low GC content are generally close totelomereandCentromereThe number of genes in these regions is relatively poor.Simchen et al confirmed that yeastGenetic recombinationI.eDouble chain fractureRelative ofincidence rateIt is coupled with the GC rich region of chromosome, and the recombination frequency of different chromosomes is different. The recombination of smaller chromosomes I, III, IV and IXFrequency ratioThe average recombination frequency of the whole genome is high.
Another obvious feature of yeast genome is that it contains a lot of DNARepeating sequence, some of which are identical DNA sequences, such asrDNAAnd CUP1 geneTy factorAnd its derivativesLTRSequence, etc.In geneticBay areaContains a large number ofTrinucleotide repeat, has aroused great attention.Because some peopleGenetic diseaseIt is caused by the change of repeat number of trinucleotide.There are more DNA sequences with higherHomologyThese DNA sequences are called genetic redundancy.The end of multiple chromosomes in yeast has a height of more than dozens of kbCognate regionThey are the main areas of genetic surplus, and these areas are still frequentDNA recombinationProcess.Another form of genetic surplus is singleGene duplicationAmong them, the dispersed type is the most typical, and there is another rare type that is clusteredgene family。Cluster homology region (CHR) is a large homologous segment located on multiple chromosomes revealed by yeast genome sequencing. Each segment contains multiple correspondingHomologous geneTheir sequence and transcription direction are very conservative, and small fragments may be inserted or deleted.These characteristics indicate that the cluster homologous region is between the large chromosomeFragment repetitionBetween and fully differentiatedIntermediate productTherefore, it is a good material for studying genome evolution and is called the fossil of gene duplication.chromosomeEnd repeat, single gene duplication and cluster homologous regions constitute the general structure of genetic surplus of yeast genome.Research shows that a group of genes in genetic surplus often have the same or similarphysiological functionTherefore, the mutation of a single gene or a few genes in them cannot show a recognizable phenotype, which is very unfavorable to the functional research of yeast genes.Therefore, many yeast geneticists believe that understanding the true nature and functional significance of genetic abundance and developing relevant experimental methods are the main difficulties and central issues in revealing the functions of all genes in the yeast genome.
gene
With the achievement of advancedEukaryoteaddedgenetic informationIt will be found that more yeast genes and higher eukaryotic genes haveHomologyTherefore, the role of yeast genome in the field of bioinformatics will become more important, which in turn will promote the research of yeast genome.Compared with yeast, higher eukaryotes have more abundant phenotypes, which makes up for the lack of obvious phenotypic changes in some gene mutations in yeast.The examples to be mentioned below just illustrate that yeast andhuman genomeStudy the relationship of mutual promotion.human beingsXeroderma pigmentosumIs a kind ofAutosomal recessive inheritanceThe skin disease ofSkin cancer。As early as 1970, Cleaver et al. reported that xeroderma pigmentosum andultraviolet raysSensitive yeast mutants are associated with the lack ofNucleotide excision repairNucleotide exception repair (NER).In 1985, the first NER pathway related gene was sequenced and confirmed to be the RAD3 gene of yeast.In 1987, Sung first reported that yeast Rad3p could repair DNA in eukaryotic cellsHelicaseThe defect of vitality.In 1990, people cloned the xeroderma pigmentosum related gene xPD, and found that it has high homology with the yeast NER pathway RAD3 gene.Later, it was found that all human NER genes could find homologous genes in yeast.The major breakthrough came from 1993, when it was found that human xPBp and xPDp are both basic components of TFIIH complex of RNA polymerase II in the transcription mechanism.Therefore, people speculated that the homologous genes (RAD3 and RAD25) of xPBp and xPDp in yeast should also have similar functions. Based on this clue, satisfactory results were quickly obtained and the original guess was confirmed.
Yeast asModel organismIts role is not only in bioinformatics, but also provides an experimental system that can be detected for higher eukaryotes.For example, you can useHeterologous geneIt complements the function of yeast gene to confirm the function of gene.According to Bassett's incomplete statistics, by July 15, 1996, at least 71 pairs ofComplementary gene。
Yeast can grow in the range of pH 3.0~7.5, and the optimal pH is 4.5~5.0.
water content
Like bacteria, yeast must have water to survive, but yeast needs less water than bacteria. Some yeast can grow in an environment with very little water, such as honey and jam, which shows that they are good atosmotic pressureThere are quite highTolerance。
temperature
When the temperature is lower than the freezing point of water or higher than 47 ℃, yeast cells generally cannot grow, and the optimal growth temperature is generally 20~30 ℃.
oxygen
Yeasts can grow in both aerobic and anaerobic environments, that is, yeasts areFacultative anaerobeIn the presence of oxygen, it decomposes sugar into carbon dioxide and water, and yeast grows faster.In the absence of oxygen, yeast decomposes sugar into alcohol and carbon dioxide.
purpose
The most frequently mentioned yeast isSaccharomyces cerevisiae(Also calledBaker's yeast）(Saccharomyces cerevisiae). Since thousands of years ago, humans have used it to ferment bread andliquor, in fermented bread andSteamed bunsIn the process, carbon dioxide will be released from the dough.
As a simple single cell eukaryote, yeast is easy to cultivate and grows rapidly, so it is widely used in modern biological research.For example, as an important model organism, Saccharomyces cerevisiae is also a genetic andmolecular biologyImportant research materials.
Dry food with no fermenting power for human consumptionyeast powderorGranularProducts.It can be recycledBeerYeast mud from the factory, or specially cultivated and dried for human nutrition.The United States, Japan and some European countriesGrain productsasbread, cakes, biscuits andSconesAbout 5% edible yeast powder is added to improve the nutritional value of food.yeastAutolysateIt can be used as meatJam, soupscheese, bread, vegetables andflavoringAdditives;stayBaby Food, health food asfood nutrition reinforcement 。5 ′ -nucleotideIt can be used as reinforcement in combination with monosodium glutamateFood flavorAdditives.Concentrate extracted from yeastInvertaseUsed as a square eggFilled chocolateLiquefier.From towheyExtracted from yeast produced from raw materialslactase, which can be used in milk processing to increase sweetness and preventlactoseThe product can meet the needs of lactose intolerant consumers.[4]
In Taiwan's frozen top mountain area, people are makingOolong TeaFirst, the tea will be blanched, and then low-temperature fermentation will be carried out. After fermentation, the yeast will retire and settle at the bottom.However, the yeast at this time has already absorbed the essence nutrients of oolong tea, picked it up, washed, disinfected, dried and other remanufacturing processes, and became tea yeast.
There are three kinds of tea yeast in the market:
one
As mentioned above, the production of tea yeast is very low, and there is almost no production, because it is difficult to collect after separating with tea;
two
Oolong TeaIt is dried together with the fermentation liquid and crushed into powder, which is basically oolong tea with little yeast;
three
Oolong tea extract andbeer yeastThe extract is formed, which is easy to collect and process, and can be produced on a large scale.
Tea yeast is widely used, and the most popular one is suitable for weight loss.
Tea yeast -- containingtea polyphenolsHas a higher thanvitamin E10 times antioxidant capacity, can reduce bloodNeutral fatThe content can effectively reduce blood fat.It can also improve the symptoms caused by obesity and high blood fatMental malaise, sleepyalkaloid, make you energetic.beer yeast-- More abundantvitamin BIt is equivalent to three times of tea yeast,Yeast chromiumTwo times as much as tea yeast,B vitaminsCan acceleratecarbohydrateThe metabolism of fat and fast consumption of calories make people energetic while slimming;Yeast chromium reduces neutral fat and helpsinsulinAccelerate the metabolism of sugar.
The concept of real tea yeast should be: containing oolong tea and other slimming productsActive ingredientAnd has the characteristics of yeast. Beer yeast is also a popular product for weight loss, which shows that yeast itself is effective for weight lossTea yeastIts advantages are that it has the characteristics of tea weight loss and yeast weight loss, which is healthier, more effective and safer.
According to the ratio of cell length and width, beer yeast can be divided into three groups.The cells in the first group are mostly round, oval or oval (cell length/width<2), mainly used foralcohol fermentation, brewing beverage wine and bread production.Group IIThe shape of the cells is mainly oval and long oval, and there are also round or short oval cells (cell length/width ≈ 2).This kind of yeast is mainly used for brewingWineandfruit wine, can also be used for beerDistilled liquorAnd yeast production.The cells in the third group were oblong (cell length/width>2).This kind of yeast has high toleranceosmotic pressureAnd high concentration salt, suitable forCane Molasses Produce alcohol for raw materials.[5]
Crushing yeast: blocky products containing 70~73% water produced by Saccharomyces cerevisiae.It is light yellow, has compact structure, is easy to crush, and has strongHairdoAbility.The products that can be stored for 2 to 3 months at 0 ℃ were initially put intocentrifugalAfter the yeast milk is pressed and dehydrated, it is called pressed yeast, commonly known as fresh yeast.Fresh compressed yeast should not be refrigerated for too long. If it is stored for too long, the yeast will begin to turn brown, and if the cold storage period is extended, the yeast can be used asBulking agentThe effect of will be reduced.When baking, its amount is 1~2% of the flour, and the baking temperature is 28~30 ℃. If the temperature exceeds 54 ℃, the yeast will lose its activity.The dough setting time varies with yeast consumption, dough setting temperature, sugar content of dough and other factors, generally 1~3 hours.
two
Active dry yeast: the dry yeast product with a moisture content of about 8%, granular, and dough forming ability produced by Saccharomyces cerevisiae.Fresh yeast is obtained by culturing yeast with drying resistance and stable fermentation power, and then it is made by extrusion and drying.The fermentation effect is similar to that of the squeezing yeast.Vacuum or filling for productsinert gas(such as nitrogen or carbon dioxide)aluminum foilBag or metal can packaging, shelf life is half a year to one year.Compared with crushed yeast, it has the advantages of long storage period, no low-temperature storage, convenient transportation and use, etc.
three
Rapid active dry yeast: a new type of fine granular product (less than 1mm in diameter) with rapid and efficient fermentation power.The moisture content is 4-6%.It is based on active dry yeastgenetic engineeringThe highly dry resistant Saccharomyces cerevisiae strain obtained by the technology ofNutritionProportioning and strictProliferation cultureConditions and drying with fluidized bed drying equipment.Same as active dry yeast, it is stored in vacuum or inert gaslifeMore than 1 year.Compared with active dry yeast, it has smaller particles and higher fermentation power. It can be directly mixed with flour and added with water to make dough for fermentation without first hydration. It can be fermented in a short timeBakingInto food.
In the actual production of bread, yeast fermentation is affected by the following factors:
Temperature:Within a certain temperature range, with the increase of temperature, the fermentation speed of yeast and gas production also increase, but the maximum temperature should not exceed 38 ℃~39 ℃.Generally, the normal temperature should be controlled within 26 ℃~28 ℃. If the rapid production rule is used, the temperature should not exceed 30 ℃, because if the temperature is exceeded, the fermentation will be too fast, the dough will not be fully mature, and the gas holding capacity will be poor, affecting the finalProduct quality。
PH value: The pH value of dough is most suitable between 4 and 6.
Effect of sugar: The sugar that can be directly used by yeast is glucose,fructose。Sucrose needs to pass through theInvertaseIt can be decomposed into glucose and fructose, and then provide energy for fermentation.alsomalt dust, made from flouramylaseIt is obtained by decomposing broken starch in flourMaltaseTransformed into 2 moleculesglucoseIt can also be used later.
Osmotic pressure:osmotic pressureIt refers to the additional pressure added to the solution to prevent osmosis. The osmotic pressure of external media has a greater impact on the vitality of yeast.Because the outer layer of yeast cellcell membraneIt's aSemipermeable membrane, that is, withInfiltrationTherefore, the concentration of external media will directly affect the vitality of yeastinorganic saltAnd other soluble solid substances will cause highOsmotic pressure, inhibit yeast fermentation.The reason is that when the concentration of external media is high, the protozoa in the yeast ooze out of the cell membrane,ProtoplasmThe yeast was destroyed and could not survive due to the separation of plasma.In this respect, dry yeastFresh yeastMore powerfuladaptability。Of course, some yeast can still survive and ferment at high concentrations.
In the production of bread, sugar and salt are the two main raw materials that affect the osmotic pressure.When theSugar contentWhen it is 0~5%, it cannot ferment yeastinhibition, on the contrary, it can promote yeastFermentation。When it exceeds 6%, it will inhibit the fermentation. If it exceeds 10%, the fermentation speed will significantly slow down,fructose, sucrose andmalt dustThe inhibitory effect of maltose is smaller than that of the first three sugars, because the osmotic pressure of maltose is lower than that of other sugars.
Salt has higher osmotic pressure and greater inhibition on yeast fermentation. When the amount of salt reaches 2%, the fermentation will be affected.
medical
The manufacturing method and properties are the same as those of food yeast.Because it contains richprotein、vitaminAnd enzymes, etcPhysiologically active substance, which is made from medicineYeast tabletasSaccharated Yeast Teblets, used to treat patients caused by unreasonable dietindigestionSymptoms.The weak people can adjust the metabolism function to a certain extent after taking it.In the process of yeast culture, such as adding some special elements to make selenium, chromium, etctrace elementIt has certain curative effect on some diseases.If includedSelenium yeastFor treatmentKeshan diseaseandKashin Beck disease, and certain preventionCell senescenceThe role of;Chromium containing yeast can be used for treatmentdiabetesEtc.
Feed
Feed yeast: usually usedCandidaOr Kleveromyces fragilis, which is made by culturing and drying, has no fermentation power, and the cells are in a dead state of powder or granular products.It is rich in protein (about 30-40%)B vitamins、amino acidAnd other substances, widely used asanimal feedProtein supplements for.It can promote animal'sGrowth and development, shorten the feeding period, increase the meat and eggs, improve the meat quality andLean meat percentage, fur improvingglossAnd can enhance the disease resistance of young poultry and livestock.
Make hair noodles
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makeHairdoThere are many waysbaking sodaHair noodles and yeast hair noodles, etc.
These methods have the same effect, that is, by generating a large amount of carbon dioxide gas in the dough, the carbon dioxide expands when heated during the cooking process, so the pasta becomes soft and delicious.
Yeast leavening is accomplished through the biological process of yeast fermentation and improves the nutritional value.
Yeasts are divided into fresh yeast and dry yeast, which are edible and nutritious single cell microorganisms,NutritionIt is called "inexhaustible source of nutrition".In addition to protein, carbohydratelipidIn addition, yeast is also rich in vitamins, minerals and enzymes.Experiments have proved that every kilogram of dry yeast contains protein equivalent to 5kg of rice, 2kg of soybeans or 2.5kgporkProtein content.Therefore,Steamed bunsThe nutritional content of bread is higher than that of non doughPancake、noodleIt is 3-4 times higher, and the protein increases nearly twice.
Protect the liver
There is also a strongAntioxidants, can protect the liver, there are certainDetoxification。Selenium, chromium, etc. in yeastMineral energyAnti aging and anti agingtumour, PreventionArteriosclerosisAnd improve human immunity.After fermentation, a kind ofphytic acidIt can be decomposed to improve the human body's ability toNutrientsAbsorption and utilization.
Loose products
Yeast produces a large amount of carbon dioxide during dough fermentation, andglutenNetwork organizationAnd was left behindReticular tissueInside, the baking food tissue is loose and porous, and the volume is increased.
Yeast also has the function of increasing gluten expansion, so that the carbon dioxide produced during fermentation can be retained in the dough, improving the gas holding capacity of the dough.If using chemistryLoosening agentIt has no effect.
Improve flavor
Dough infermentation process Experienced a series of complex creatureschemical reaction, producing the unique fermentation flavor of bread products.At the same time, it forms the unique aroma, rich and appetizing baking fragrance of bread products.
Add in foodFlavorIt can improve the overall taste intensity of food, and can also be used to enhance some flavor characteristics of food, such as persistence, mildness, and richness.The more flavoring agent is added, the better.Research showsMSG(monosodium glutamate) has the best flavor enhancement effect at 0.2~0.8% of the food weightphosphoric acidInosineDisodium）About 0.02~0.04%, we can getequivalentThe flavor enhancement intensity of.But we should also consider the flavor andNaClScale of.If MSG and salt are added toChicken soupOr plusSpiceIn the chicken soup, the best proportion is 0.33% MSG, 0.83% NaCL, 0.38% MSG, 0.87% NaCl.Only in a specific concentration range can you give a pleasant feeling, and too much is counterproductive.
In the range of 0.6~4.0% NaCl content, when the added YE (yeast extract) content is between 0.4~3.0%, the salty taste of the solution can be enhanced.
two
When NaCl concentration is more than 7%, adding more than 0.4% YE can weaken the salty taste of the product to varying degrees, and the degree of weakening increases with the increase of NaCL concentration and the amount of YE added.
Performance characteristics of YE:
Pure natural, rich in a variety of amino acids, polypeptides, taste nucleotides.
It has delicious taste, rich aroma and strong meat quality.
High temperature resistance, which can give food a better flavor under high temperature conditions.[6]
The amino acid composition is shown in the table below:
Yeast, as a higher eukaryote, especiallyHuman geneThe most direct role of the model organism of group research is embodied in the field of bioinformatics.When people discover a new human gene with unknown function, they can quickly reach any yeastGenome databaseIn order to speed up the functional research of this human gene, we searched for the yeast gene with known homologous function and obtained the relevant information about its function.The study found that there are manyHereditary diseaseThe genes ofPhysiological function of proteinAnd their interactions with other proteins will help deepen the understanding of these genetic diseases.In addition, many important human diseases, such as earlydiabetes、Small bowel cancerAnd heart diseasePolygeneHereditary diseases reveal that all related genes involved in these diseases are a difficult and long processSimilarityIt will provide important help for us to improve the level of diagnosis and treatment.
The best example of yeast as a model organism is that those wholinkage analysisandPositioning clonesAnd then obtained by sequencing verificationHuman genetic diseasesIn the study of related genes, the latternucleotideThe sequence homology with yeast gene provides clues for its function research.For example, humansgeneticwrongpolypnatureSmall bowel cancerRelated genes and yeast MLH1, MSH2 genes,DyskinesianatureTelangiectasiaThe related gene has high homology with yeast TEL1 gene and Bloom's syndrome related gene with yeast SGS1 gene.Hereditary nonpolyposis colorectal cancer genetumor cellIt shows thatnucleotideA cell phenotype with unstable short repeat sequence. Before the human gene was cloned, researchers isolated gene mutations with the same phenotype (MSH2 and MLH1 mutations) in yeast.Inspired by this result, people speculate that the small intestine cancer gene is the homologous gene of MSH2 and MLH1, and theynucleotide sequenceOnHomologyThis hypothesis is further confirmed.Bloom's syndrome is a clinical manifestation ofsexual precocityThe patient's cells show a shortened life cycle phenotype when cultured in vitro, and its related genes are encoded in yeastSnail enzymeSGS1 gene has high homology.Similar to cultured cells from individuals with Bloom's syndrome, yeast cells with SGS1 gene mutations exhibit significantly shortened life cycles.Francoise et al. studied more than 170Feature cloning42% of the human genes obtained have obvious homology with yeast genes, and most of the coding products of these human genes aresignal transduction pathway、Membrane transportperhapsDNA synthesisIt is related to repair, while human genes that have no obvious homology with yeast genes mainly code someMembrane receptor, blood orimmune systemComponents, or human specificMetabolic pathwaySome important enzymes and proteins in C.
engineering application
Yeasts of unicellular eukaryotes have relatively completeGene expression regulationMechanism and the ability to process and modify the expressed product.Saccharomyces Cerevisiaemolecular geneticsThe aspect was first recognized by people and was also the first to actExogenousgene expressionThe yeast host of.In 1981, Saccharomyces cerevisiae expressed the firstforeign gene----interferonGene, and then a series of foreign genes were expressed in the system. Although interferon and insulin have been produced in large quantities and widely used by Saccharomyces cerevisiae, the results of the laboratory were very encouraging when it was prepared by Saccharomyces cerevisiae, but when the laboratory was expanded to industrial scale, its output declined rapidly.as a result ofculture mediumMiddle vit plasmid highcopy numberOfSelect pressureThe lost plasmid became unstable and the copy number decreased.Copy number is an essential factor for high expression, so the decrease of copy number also directly leads to the decrease of foreign gene expression.At the same time, the composition of the culture medium used in the laboratory is complex and expensive. When the culture medium acceptable to the industrial scale is used, the output will decline.In order to overcome the limitations of Saccharomyces cerevisiae, Wegner and others in the United States first developedMethylotrophic yeast(methylotropic yeast) as the representative of the second generation yeast expression system.Methylotrophic yeasts include Pichia, Candida, etc.Pichia Pastoris（pichia pastoris ）In recent years, the host gene expression system has developed most rapidly and been widely used.pichia pastoris The reason why the system is widely used is that it has the characteristics of ordinary yeast.
Candida:Can causeThrushas well asurethritisAnd other infectious diseases.Candida albicans mainly appear on the mucous membrane of oral cavity, intestinal tract, urethra and other parts of human body, and a small part lives on the skin surfaceNormally,CandidaIt exists in yeast cell type, withoutPathogenicity；Under the induction of some factors, such as immune deficiency, excessive use of antibiotics, Candida albicans is transformed intomyceliumGrowth form, and multiply in large numbers, invade the patient's mucosal system, causing inflammation and morbidity.In the bosomLate pregnancytakeacyeterionOf women are highly susceptible to infectionurethritisOne possible cause is the imbalance of hormones in the body.
whiteCryptococcusCryptococcus albidus: It is a kind of budding yeast that is generally harmless to human beings.But in people with immune system defects, it may infect patients and cause a disease calledCryptococcosis(cryptococcus).In addition, there are cases that one personImmunosuppressive therapyThe pulmonary infection caused by Cryptococcus albicans in 30% of patients led to acuterespiratory distress syndrome（ARDS）Symptoms of.
Saccharomyces cerevisiae(Saccharomyces serviciae): Generally not considered as conditionalpathogenic bacteriaHowever, there are also a few reports showing that Saccharomyces cerevisiae has pathogenic ability.
product development
Announce
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As early as 3000 BC, humans began to use yeast to produce fermentation products.The first product to be sold on the market is yeast paste, which is characterized by fast fermentation, but inconvenient transportation and use, and the commercialization of the product is limited.From the sales of yeast paste, yeast manufacturing as an industry has a history of more than 200 years.Yeast has become one of the most studied microorganisms in the world and is a biotechnology product todayResearch and developmentHot spots andModern biotechnologyDevelopmentgenomeThe mode system studied.
Since the 1980s, China's yeast industry has achievedLeap forward developmentIt has a globally popular independent innovation brand, and the research, production and application of yeast products have reached the international advanced level.
The research team used yeast with about 6000 genes to conduct experiments and investigate the maximum number of copies of all its genes, that is, to what extent the number of copies of genes will lead to cell death.The results showed that more than 80% of the genes were replicated more than 100 times respectively, and the yeast cells still maintained normal functions.However, 115 genes that replicate only several times will lead to yeast death.Most of these genes are related toIntracellular transportandCytoskeletonAnd other basic functions, as well as genes related to manufacturing cellsproteinorProtein complexofThe research team believes that after these genes are duplicated several times, they lead to unnecessary synthesis or decomposition of a large number of proteins, causing a burden on cells, causing serious imbalance in yeast, which leads to yeast death.
