微生物学英文教学课件：chapter5 Microbial Nutrition

1、PART IIIIMicrobial Nutrition,Microbial Nutrition,Growth, and ControlGrowth, and ControlChapter 5 Microbial NutritionNutrient requirementsNutritional types of microorganismsUptake of Nutrients by the Cell Outline: Nutrition Nutrition is a process by which chemical substances called nutrientsnutrients

2、 are acquired from the environment and used in cellular activities such as metabolism and growth. With respect to nutrition,microbes are not really so different from humans and plants. Microorganisms require about nine elements in large quantities, because they are used to construct carbohydrates, l

3、ipids, proteins, and nucleic acids. Several other elements are needed in very small amounts and are parts of enzymes and cofactors.Concepts:5.1 Nutrient requirementsMacronutrients 95% or more of cell dry weight is made up of a few major elements: carbon, oxygen, hydrogen, nitrogen, sulfur, phosphoru

4、s, potassium, calcium and magnesium . The first six ( C, H, O, N, P and S) are components of carbohydrates, lipids, proteins and nucleic acids.Trace Elements/ micronutrientsMicrobes require very small amounts of other mineral elements, such as iron, copper, molybdenum, and zinc; these are referred t

5、o as trace elements. Most are essential for activity of certain enzymes, usually as cofactors. Finally, it must be emphasized that microorganisms require a balanced mixture of nutrients. If an essential nutrient is in short supply, microbial growth will be limited regardless of the concentrations of

6、 other nutrients.Major nutritional typeSources of energy, hydrogen/electrons, and carbonRepresentative microorganismsPhotoautotroph (Photolithotroph)Light energy, inorganic hydrogen/electron(H/e-) donor, CO2 carbon sourceAlgae, Purple and green bacteria, CyanobacteriaPhotoheterotroph (Photoorganotro

7、ph)Light energy, inorganic H/e- donor, Organic carbon sourcePurple nonsulfur bacteria, Green sulfur bacteriaChemoautotroph(Chemolithotroph)Chemical energy source (inorganic), Inorganic H/e- donor, CO2 carbon sourceSulfur-oxdizing bacteria, Hydrogen bacteria,Nitrifying bacteriaChemoheterotroph(Chenoo

8、rganotroph) Chemical energy source (organic), Organic H/e- donor, Organic carbon sourceMost bacteria, fungi, protozoa5.2 Nutritional types of microorganismsAlgae, CyanobacteriaCO2 + H2O Light + Chlorophyll （CH2O） +O2Purple and green bacteriaCO2 + 2H2S Light + bacteriochlorophyll （CH2O） + H2O + 2SPur

9、ple nonsulfur bacteria (Rhodospirillum)CO2 + 2CH3CHOHCH3 Light + bacteriochlorophyll （CH2O） + H2O + 2CH3COCH3Photoautotroph:Photoheterotroph:PropertycyanobacteriaGreen and purple bacteriaPurple nonsulfur bacteriaPhoto - pigmentChlorophyllBcteriochlorophyllBcteriochlorophyllO2 productionYesNoNoElectr

10、on donorsH2OH2, H2S, SH2, H2S, SCarbon sourceCO2CO2Organic / CO2Primary products of energy conversionATP + NADPHATPATPProperties of microbial photosynthetic systemsChemoautotroph:Nitrifying bacteria2 NH4+ + 3 O2 2 NO2- + 2 H2O + 4 H+ + 132 KcalBacteriaElectron donorElectron acceptorProductsAlcaligen

11、s and Pseudomonas sp.H2O2H2ONitrobacterNO2-O2NO3- , H2ONitrosomonasNH4+O2NO2- , H2ODesulfovibrioH2SO4 2-H2O. H2SThiobacillus denitrificansS0. H2SNO3-SO4 2- , N2Thiobacillus ferrooxidansFe2+O2Fe3+ , H2O Although a particular species usually belongs in only one of the four nutritional classes, some sh

12、ow great metabolic flexibility and alter their metabolic patterns in response to environmental changes. These microbes are sometimes called mixotrophicmixotrophic because they combine chemolithoautotrophic and heterotrophic metabolic processes. This sort of flexibility seems complex and confusing, y

13、et it gives its possessor a definite advantage if environmental conditions frequently change. Microorganisms often grow and reproduce when minerals and sources of energy, carbon, nitrogen, phosphorus, and sulfur are supplied. These organisms have the enzymes and pathways necessary to synthesize all

14、cell components required for their well-being.5.3 Growth Factors Many microorganisms, on the other hand, lack one or more essential enzymes. Therefore they cannot manufacture all indispensable constituents but must obtain them or their precursors from the environment. Few microbes are as versatile a

15、s Escherichia coli in assembling molecules from scratch. Many fastidious bacteria lack the genetic and metabolic mechanisms to synthesize every organic compound they need for survival. An organic compound such as an amino acid, nitrogen base, or vitamin that cannot be synthesized by an organism and

16、must be provided as a nutrient is a growth factorgrowth factor. . Growth Factors Amino acids are needed for protein synthesis, purines and pyrimidines for nucleic acid synthesis. Vitamins are small organic molecules that usually make up all or part enzyme cofactors, and only very small amounts are r

17、equired for growth. (1)amino acids, (2) purines and pyrimidines, (3) vitamins5.4 Culture medium and its physiological function Any culture medium should contain six nutrient elements that microorganisms need for growing: Water, Carbon Sources, Nitrogen Sources,Inorganic Salts/ minerals, Growth Facto

18、rs and Energy Sources1.Water Water content is the highest component of the cells (70%-90%). All cells require water from their environment to sustain growth and metabolism.(the diffusion of nutrients and wastes.) Water is the solvent for cell chemicals, and it is needed for enzyme function and diges

19、tion of macromolecules. Water can regulate and control the environmental temperature(Higher specific heat,faster heat-transport)2. Carbon sources They Constitute the carbonic framework of the cell materials and the metabolites. Carbon sources frequently also serve as energy sources. Carbon sources i

20、n common use:carbohydrates, alcohol,lipids,organic acid, hydrocarbon, protein etc. Carbohydrates are best carbon sources for heterotroph microorganisms.(Glucose is most common used in lab.)3. Nitrogen Sources They Constitute the nitrogen framework of the cell materials and the metabolites.(but canno

21、t serve as energy sources.) Inorganic nitrogen sources: NO3-, NO2-, or NH4+). Organic nitrogen sources:peptone,beef extract,yeast extract.4. Inorganic Salts/ minerals Mineral ions are normally a part of enzymes and cofactors, and they serve as cofactors for many enzymes or are required for activity

22、by a number of enzymes. maintenance of cell structure. regulate osmotic pressure. Control oxidation-reduction potential. Sometimes serve as energy sources for some microorganisms. Mineral ions in common use: sulphate,phosphate,chloride,compounds contained K,Na,Ca,Mg,Fe.5. growth factors Organic comp

23、ounds that cannot be synthesized with ordinary carbon or nitrogen sources by an organism and must be provided as small quantity of nutrients are growth factors.growth factors. There are four classes of growth factors: (1) amino acids, (2) purines and pyrimidines, (3) vitamins and (4)lipoids. They se

24、rve as coenzymes or cofactors to take part in enzyme-catalyzed reactions. They are provided from peptone,beef extract,yeast extract in the lab.And there are a various of growth factors in wort or rice medium.6. Energy Sources Light energy and Chemical energy5.5 Uptake of Nutrients by the Cell5.5 Upt

25、ake of Nutrients by the Cell Since microorganisms often live in nutrient-poor habitats, they must be able to transport nutrients from dilute solutions into the cell against a concentration gradient. Nutrient molecules must pass through a selectively permeable plasma membrane that will not permit the

26、 free passage of most substances. Nutrient molecules frequently cannot cross selectively permeable plasma membranes through passive diffusion and must be transported by one of three major mechanisms involving the use of membrane carrier proteins.Uptake of nutrients 1. Phagocytosis Protozoa2. Permeab

27、ility absorption Most microorganisms passive transport /simple diffusion facilitated diffusion active transport group translocationA few substances, such as glycerol, can cross the plasma membrane by passive diffusion. Passive diffusion is the process in which molecules move from a region of higher

28、concentration to one of lower concentration as a result of random thermal agitation. 1. passive diffusion The rate of passive diffusion is dependent on the size of the concentration gradient between a cells exterior and its interior. Very small molecules such as H2O, O2, and CO2 often move across me

29、mbranes by passive diffusion. Larger molecules, ions, and polar substances do not cross membranes by passive or simple diffusion.The rate of diffusion across selectively permeable membranes is greatly increased by the use of carrier proteins, sometimes called permeases, which are embedded in the pla

30、sina membrane. Since the diffusion process is aided by a carrier, it is called facilitated diffusion. The rate of facilitated diffusion increases with the concentration gradient much more rapidly and at lower concentrations of the diffusing molecule than that of passive diffusion. 2. Facilitated dif

31、fusionThe membrane carrier can change conformation after binding an external molecule and subsequently release the molecule on the cell interior. It then returns to the outward oriented position and is ready to bind another solute molecule. A model of facilitated diffusionBecause there is no energy

32、input, molecules will continue to enter only as long as their concentration is greater on the outside. Facilitated diffusion does not seem to be important in procaryotes because nutrient concentrations often are lower outside the cell so that facilitated diffusion cannot be used in uptake. Glycerol

33、is transported by facilitated diffusion in E. coli, Salmonella typhimurium, Pseudomonas, Bacillus, and many other bacteria. The process is much more prominent in eucaryotic cells where it is used to transport a variety of sugars and amino acids. Microorganisms often live in habitats characterized by

34、 very dilute nutrient sources, and, to flourish, they must be able to transport and concentrate these nutrients. Thus facilitated diffusion mechanisms are not always adequate, and other approaches must be used. The two most important transport processes in such situations are active transport and gr

35、oup translocation, both energy-dependent processes.Active transport is the transport of solute molecules to higher concentrations, or against a concentration gradient, with the use of metabolic energy input. 3. Active transport(1) primary active transport Binding protein transport systems or A ATP-T

36、P-b binding inding c cassette transporters (ABC assette transporters (ABC transporters) transporters) are active in bacteria, archaea, and eucaryotes. The membrane-spanning domains form a pore in the membrane and the nucleotide-binding domains bind and hydrolyze ATP to drive uptake. E. coli transpor

37、ts a variety of sugars (arabinose, maltose, galactose, ribose) and amino acids (glutamate, histidine, leucine) by this mechanism.(2) secondary active transport Bacteria also use proton gradients generated during electron transport to drive active transport. The membrane transport proteins responsibl

38、e for this process lack special periplasmic solute-binding proteins. The lactose permease of E. coli is a well-studied example. The permease is a single protein having a molecular weight of about 30,000. It transports a lactose molecule inward as a proton simultaneously enters the cell (a higher con

39、centration of protons is maintained outside the membrane by electron transport chain activity). Such linked transport of two substances in the same direction is called symportsymport. . Here, energy stored as a proton gradient drives solute transport. E. coli also uses proton symport to take up amin

40、o acids and organic acids like succinate and malate. Although the mechanism of transport is not completely understood, it is thought that binding of a proton to the transport protein changes its shape and affinity for the solute to be transported. A proton gradient also can power active transport in

41、directly, often through the formation of a sodium ion gradient. For example,an E. coli sodium transport system pumps sodium outward in response to the inward movement of protons (figure figure 5.45.4). Such linked transport in which the transported substances move in opposite directions is termed an

42、tiportantiport. . The sodium gradient generated by this proton antiport system then drives the uptake of sugars and amino acids. A sodium ion could attach to a carrier protein, causing it to change shape. The carrier would then bind the sugar or amino acid tightly and orient its binding sites toward

43、 the cell interior. Because of the low intracellular sodium concentration, the sodium ion would dissociate from the carrier, and the other molecule would follow. E. coli transport proteins carry the sugar melibiose and the amino acid glutamate when sodium simultaneously moves inward. Sodium symport

44、or cotransport also is an important process in eucaryotic cells where it is used in sugar and amino acid uptake. ATP, rather than proton motive force, usually drives sodium transport in eucaryotic cells. Often a microorganism has more than one transport system for each nutrient, as can be seen with

45、E. coli. This bacterium has at least five transport systems for the sugar galactose, three systems each for the amino acids glutamate and leucine, and two potassium transport complexes. When there are several transport systems for the same substance, the systems differ in such properties as their en

46、ergy source, their affinity for the solute transported,and the nature of their regulation. Presumably this diversity gives its possessor an added competitive advantage in a variable environment. 4. Group translocationThe best-known group translocation system is the phosphoenolpyruvate: sugar phospho

47、transferase system (PTS), which transports a variety of sugars into procaryotic cells while Simultaneously phosphorylating them using phosphoenolpyruvate (PEP) as the phosphate donor.Group translocationPEP + sugar (outside) pyruvate + sugar-P (inside)The phosphoenolpyruvate: sugar phosphotransferase

48、 system of E. coli. The following components are involved in the system: phosphoenolpyruvate, PEP; enzyme 1, E I; the low molecular weight heat-stable protein, HPr; enzyme 11, E II. The PTS is quite complex. In E. coli and Salmonella typhimurium. HPr and enzyme I(EI) are cytoplasmic. Enzyme II(EII)

49、is more variable in structure and often composed of three subunits or domains. EIIA is cytoplasmic and soluble. EIIB also is hydrophilic but frequently is attached to EIIC, a hydrophobic protein that is embedded in the membrane. PTSs are widely distributed in procaryotes. Except for some species of

50、Bacillus that have both glycolysis and the phosphotransferase system, aerobic bacteria seem to lack PTSs. Members of the genera Escherichia, Salmonella, Staphylococcus, and other facultatively anaerobic bacteria have phosphotransferase systems; some obligately anaerobic bacteria (e.g., Clostridium)

51、also have PTSs. Many carbohydrates are transported by these systems. E. coli takes up glucose, fructose, mannitol, sucrose, N-acetylglucosamine, cellobiose, and other carbohydrates by group translocation. ItemsPassive diffusionFacilitated diffusionActive transportGroup translocationcarrier proteins

52、NonYesYesYestransport speedSlow Rapid Rapid Rapid against gradientNonNonYesYestransport moleculesNo specificity Specificity Specificity Specificity metabolic energy No needNeedNeedNeedSolutes moleculesNot changedChangedChangedChangedSimple comparison of transport systemsSummary 1. Microorganisms req

53、uire nutrients, materials that are used in biosynthesis and energy production.2. Macronutrients or macroelements (C, O, H, N, S, P, K, Ca, Mg, and Fe) are needed in relatively large quantities; micronutrients or trace elements (e.g., Mn, Zn, Co, Mo, Ni, and Cu) are used in very small amounts.3. Auto

54、trophs use CO2 as their primary or sole carbon source; heterotrophs employ organic molecules.4. Microorganisms can be classified based ontheir energy and electron sources.Phototrophs use light energy, and chemotrophs obtain energy from the oxidation of chemicalcompounds. Electrons are extracted from

55、reduced inorganic substances by lithotrophsand from organic compounds by organotrophs.5. Nitrogen, phosphorus, and sulfur may beobtained from the same organic moleculesthat supply carbon, from the directincorporation of ammonia and phosphate,and by the reduction and assimilation ofoxidized inorganic molecules.6. Probably most microorganisms need growthfactors. Growth factor requirements makemicrobiological assays possible.7. Although some nutrients can enter cells by passive diffusion, a me