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1、Chapter 6 Microbial Nutrition and growth,Sources of Essential Nutrients,. Microorganisms require about ten elements in large quantities, because they are used to construct carbohydrates, lipids, proteins, and nucleic acids. Several other elements are needed in very small amounts and are parts of enz
2、ymes and cofactors,Carbon Sources (inorganic or organic) heterotroph or autotroph Hot and cold Salt, Acidity, Alkalinity Other Frontiers to Conquer Nitrogen Sources Oxygen Sources Hydrogen Sources Phosphorus Sources Sulfur Sources Other Nutrients Important in Microbial Metabolism,Macronutrients,96%
3、or more of cell dry weight is made up of a few major elements: carbon, oxygen, hydrogen, nitrogen, sulfur, phosphorus, potassium, calcium, magnesium and iron. The first six ( C, H, O, N, P and S) are components of carbohydrates, lipids, proteins and nucleic acids,Trace Elements,Microbes require very
4、 small amounts of other mineral elements(矿质元素), such as iron, copper, molybdenum(钼), and zinc(锌); these are referred to as trace elements. Most are essential for activity of certain enzymes, usually as cofactors.,Growth Factors,Amino acids for protein synthesis Purines and pyrimidines for nucleic ac
5、id synthesis. Vitamins are small organic molecules that usually make up all or part enzyme cofactors, and only very small amounts are required for growth.,(1)Amino acids (2) Purines and pyrimidines, (3) Vitamins,6.2 Nutritional types of microorganisms,Algae, Cyanobacteria CO2 + H2O Light + Chlorophy
6、ll （CH2O） +O2,Purple and green bacteria CO2 + 2H2S Light + bacteriochlorophyll （CH2O） + H2O + 2S,Purple nonsulfur bacteria (Rhodospirillum) CO2 + 2CH3CHOHCH3 Light + bacteriochlorophyll （CH2O） + H2O + 2CH3COCH3,Photoautotroph,Photoheterotroph,Properties of microbial photosynthetic systems,Chemoautot
7、roph,Nitrifying bacteria 2 NH4+ + 3 O2 2 NO2- + 2 H2O + 4 H+ + 132 Kcal,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.,Transport Mecha
8、nisms for Nutrient Absorption,Passive transport simple diffusion Facilitated diffusion Active transport Group translocation,Passive diffusion,Passive diffusion-a phenomenon in which molecules move from an area of high concentration to an area of low concentration because of random thermal agitation
9、Requires a large concentration gradient for significant levels of uptake Limited to only a few small molecules (e.g., glycerol, H2O, O2, and CO2),Facilitated diffusion,Facilitated diffusion-a process that involves a carrier molecule (permease) to increase the rate of diffusion; net effect is limited
10、 to movement from an area of higher concentration to an area of lower concentration Requires a smaller concentration gradient than passive diffusion The rate plateaus when the carrier becomes saturated (i.e., when it is binding and transporting molecules as rapidly as possible) Generally more import
11、ant in eucaryotes rather than procaryotes,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 plasina membrane. Since the diffusion process is aided by a carrier, it is called facilita
12、ted diffusion. The rate of facilitated diffusion increases with the concentratioti gradient much more rapidly and at lower concentrations of the diffusing molecule than that of passive diffusion,Facilitated diffusion,The rate of diffusion across selectively permeable membranes is greatly increased b
13、y the use of carrier proteins, sometimes called permeases, which are embedded in the plasina membrane. Since the diffusion process is aided by a carrier, it is called facilitated diffusion. The rate of facilitated diffusion increases with the concentratioti gradient much more rapidly and at lower co
14、ncentrations of the diffusing molecule than that of passive diffusion.,The 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 mole
15、cule.,A model of facilitated diffusion,Because there is no energy input, molecules will continue to enter only as long as their concentration is greater on the outside.,Active transport,Active transport-a process in which metabolic energy is used to move molecules to the cell interior where the solu
16、te concentration is already higher (i.e., it runs against the concentration gradient),Characteristics of active transport Saturable uptake rate Requires an expenditure of metabolic energy Can concentrate molecules inside the cell even when the concentration inside the cell is already higher than tha
17、t outside the cell ATP-binding cassette transporters (ABC transporters) use ATP to drive transport against a concentration gradient; they are observed in bacteria, archaea and eucaryotes Proton motive forces can also be used to power active transport,Group translocation,The best-known group transloc
18、ation system is the phosphoenolpyruvate: sugar phosphotransferase system (PTS), which transports a variety of sugars into procaryotic cells while Simultaneously phosphorylating them using phosphoenolpyruvate (PEP) as the phosphate donor.,Group translocation,PEP + sugar (outside) pyruvate + sugar-P (
19、inside),The phosphoenolpyruvate: sugar phosphotransferase 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,- and enzyme III, E III.,Growth definition,Growth may be gener
20、ally defined as a steady increase in all of the chemical components of an organism. Growth usually results in an increase in the size of a cell and frequently results in cell division. Because observing growth of single cells is difficult, microbiologists usually study growth of a population of micr
21、obes,Population Growth,Growth is defined as an increase in the number of microbial cells in a population. Growth rate is the change in cell number or cell mass per unit time. The interval for the formation of two cells from one is called a generation. The time required for this to occur is called th
22、e generation time.,A typical growth curve for a population of cells can be divided into several distinct phases called the lag phase, exponential phase, stationary phase, and death phase.,Lag Phase,Lag phase-the period of apparent inactivity in which the cells are adapting to a new environment and p
23、reparing for reproductive growth, usually by synthesizing new cell components; it varies considerably in length depending upon the condition of the microorganisms and the nature of the medium,Exponential Phase,Exponential (log) phase-the period in which the organisms are growing at the maximal rate
24、possible given their genetic potential, the nature of the medium, and the conditions under which they are growing; the population is most uniform in terms of chemical and physical properties during this period,Stationary Phase,Stationary phase-the period in which the number of viable microorganisms
25、remains constant either because metabolically active cells stop reproducing or because the reproductive rate is balanced by the rate of cell death Microbial populations enter stationary phase for several reasons including nutrient limitation, toxic waste accumulation, and possibly cell density Respo
26、nses to starvation conditions are of practical importance for medical and industrial microbiology; these responses include morphological changes and changes in gene expression and physiology,Death Phase,If incubation continues after a population reaches the stationary phase, the cells may remain ali
27、ve and continue to metabolize, but they may also die. If the latter occurs, the population is said to be in the death phase.,Measurement of Growth,Measurement of cell numbers Direct count methods do not distinguish between living and dead cells, and may be accomplished by direct microscopic observat
28、ion on specially etched slides (such as Petroff-Hausser chambers or hemacytometers) or by using electronic counters (such as Coulter Counters, which count microorganisms as they flow through a small hole or orifice),Viable Counting method,The usual practice, which is the most valid statistically, is
29、 to count colonies only on plates that have between 30 and 300 colonies. To make a 10-fold (101) dilution, one can mix 0.5 ml of sample with 4.5 ml of diluent, or 1.0 ml sample with 9.0 ml diluent.,Measurement of cell mass-may be used to approximate the number of microorganisms if a suitable paramet
30、er proportional to the number of microorganisms present is used (suitable parameters may be dry weight, light scattering in liquid solutions, or biochemical determinations of specific cellular constituents such as protein, DNA, or ATP),The Continuous Culture of Microorganisms,Used to maintain cells
31、in the exponential growth phase at a constant biomass concentration for extended periods of time (these conditions are met by continual provision of nutrients and removal of wastes),The Chemostat,A chemostat-a continuous culture device that maintains a constant growth rate by supplying a medium cont
32、aining a limited amount of an essential nutrient at a fixed rate and by removing medium that contains microorganisms at the same rate,the turbidostat,a continuous culture device that regulates the flow rate of media through the vessel in order to maintain a predetermined turbidity or cell density; t
33、here is no limiting nutrient,The Influence of Environmental Factors on Growth,The activities of microorganisms are greatly affected by the chemical and physical conditions of their environments. Understanding environmental in fluences helps us to explain the distribution of microorganisms in nature
34、and makes it possible for us to devise methods for controlling microbial activities and destroying undesirable organisms. Four main factors : Temperature, oxygen, water availability, and pH,Temperature,Temperature has a profound effect on microorganisms; as the temperature rises, there is an increas
35、e in the growth rate due to increasing the rates of enzyme reactions; eventually a temperature becomes too high and microorganisms are damaged by enzyme denaturation, membrane disruption, and other phenomena,Microorganisms are classified as psychrophiles(嗜冷的), mesophiles(嗜温的), thermophiles(嗜热的), and
36、 extremethemophiles(极度嗜热的) based on their optimal growth temperature.,Oxygen concentration,An organism able to grow in the presence of O2 is an aerobe; one that cannot is an anaerobe Obligate aerobes are completely dependent on atmospheric O2 for growth Facultative anaerobes do not require O2 for gr
37、owth, but do grow better in its presence Aerotolerant anaerobes ignore O2 and grow equally well whether it is present or not Obligate (strict) anaerobes do not tolerate O2 and die in its presence Microaerophiles require lower levels (2 to 10%) for growth because normal atmospheric levels of O2 (20%)
38、 are damaging to the cell,Water activity,If the concentration of solutes, such as sodium chloride, is higher in the surrounding medium (hypertonic), then water tends to leave the cell. The cell membrane shrinks away from the cell wall (an action called plasmolysis), and cell growth is inhibited.,Normal cell,Plasmolyzed cell,