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1、Chapter 7 Microbial Growth and Growth controlChapter 7 Microbial Growth an7.1 Overview of Cell Growth7.2 Population Growth 7.3 Measurement of Growth7.4 Continuous Culture:The Chemostat 7.5 Effect of Environment on Growth7.6 Growth Control 7.7 Viral Control7.8 Fungal Control Chapter outline7.1 Overvi
2、ew of Cell Growth C Concepts Microbial growth is defined as an increase in cellular constituents and may result in an increase in a microorganisms size,population number,or both.A wide variety of techniques can be used to study microbial growth by following changes in the total cell number,the popul
3、ation of viable microorganisms,or the cell mass.Solid objects can be sterilized by physical agents such as heat and radiation;Liquids and gases are sterilized by heat,radiation,and filtration through the proper filter.A knowledge of methods used for microbial control is essential for personal and pu
4、blic safety.Concepts Microbial growth iChapter-7-Microbial-Growth-and-Growth-control-微生物学-教学课件-英文版Chapter-7-Microbial-Growth-and-Growth-control-微生物学-教学课件-英文版G1 Primary growth phase of the cell during which cell enlargement occurs,a gap phase separating cell growth from replication of the genomeS Pha
5、se in which replication of the genome occursG2 Phase in which the cell prepares for separation of the replicated genomes,this phase includes synthesis of microtubules and condensation of DNA to form coherent chromosomes,a gap phase separating chromosome replication from miosis.M Phase called miosis
6、during which the microtubular apparatus is associated and subsequently used to pull apart the sister chromosomes.Cell life cycle in Eukaryotic cellsG1 Primary growth Eukaryotic cell:Prokaryotic cell:G1 S G2 M G1 R DEukaryotic cell:G1 SMost bacterial cells reproduce asexually by binary fision,a proce
7、ss in which a cell divides to produce two nearly equal-sized progeny cells.Three processes:Increase in cell size(cell elongation)DNA replication Cell divisionBinary fisionMost bacterial cells reproduceChapter-7-Microbial-Growth-and-Growth-control-微生物学-教学课件-英文版7.2 Population GrowthGrowth is defined a
8、s 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 the generation time.7.2 Population GrowthGrowth
9、 is A growth experiment beginning with a single cell having a doubling time of 30 min is presented.This pattern of population increase,where the number of cells doubles during each unit time period,is referred to as exponential growth.Exponential Growth A growth experiment beN=N02n N=final cell numb
10、er.N0=initial cell number,and n=number of generations.n=(log N0 log N)/log 2 =(log N0 log N)/0.301=3.3(log N log N0).The generation time g of the cell population is calculated as t/n,where t is simply the hours or minutes of exponential growth.Calculating Generation TimesN=N02n N=final cell numGrowt
11、h Cycle of PopulationsA 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.Growth Cycle of PopulationsA tGrowth curve of bacteria1.Lag Phase 2.Exponential Phase 3.Stationary Phase4.Death P
12、hase Growth curve of bacteriaLag Ph Lag Phase When a microbial population is inoculated into a fresh medium,growth usually does not begin immediately but only after a period of time called the lag phase,which may be brief or extended depending on the history of the culture and growth conditions.This
13、 happens because for growth to occur in a particular culture medium the cells must have a complete complement of enzymes for synthesis of the essential metabolites not present in that medium.Lag Phase When a microb Exponential Phase It is a consequence of the fact that each cell divides to form two
14、cells,each of which also divides to form two more cells,and so on.Most unicellular microorganisms grow exponentially,but rates of exponential growth vary greatly.In general,prokaryotes grow faster than eukaryotic microorganisms Exponential Phase It is a If a single bacterium continued to grow expone
15、ntially for 48 hr,produce a population that weighed about 4000 times the weight of Earth!This is particularly impressive because a single bacterial cell weighs only about one-trillionth(10 l2)of a gram.Stationary PhaseAn essential nutrient of the culture medium is used up or some waste product of th
16、e organism builds up in the medium to an inhibitory level and exponential growth ceases,or both.If a single bacterium con If incubation continues after a population reaches the stationary phase,the cells may remain alive and continue to metabolize,but they may also die.If the latter occurs,the popul
17、ation is said to be in the death phase.Death Phase If incubation continues af Population growth is measured by following changes in the number of cells or weight of cell mass.7.3 Measurement of Growth Population growth is measur The number of cells in a population can be measured by counting a sampl
18、e under the microscope,either on samples dried on slides or on samples in liquid.With liquid samples,special counting chambers must be used.Total Cell CountDirect microsopic counting procedure using the Petroff-Hausser counting chamber.The number of cells in The usual practice,which is the most vali
19、d statistically,is 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.Viable Counting method The usual practice,whichThe usual way to perform a viable count is
20、to determine the number of cells in the sample capable of forming colonies on a suitable agar medium.There are two ways of performing a plate count:the spread plate method and the pour plate method.In either case the sample must usually be diluted before plating.The usual way to perform a viaChapter
21、-7-Microbial-Growth-and-Growth-control-微生物学-教学课件-英文版The number of colonies obtained in a viable count depends not only on the inoculum size but also on the suitability of the culture medium and the incubation conditions used;It also depends on the length of incubation.The length of incubation.Some t
22、iny colonies may be missed during the counting.The incubation conditions(medium,temperature,time).Key dilutions must be prepared.Sources of Error in Plate CountingThe number of colonies obtaine A cell suspension looks cloudy(turbid)to the eye because cells scatter light passing through the suspensio
23、n.The more cells present,the more light scattered and hence the more turbid the suspension.Turbidimetric Measurements of Cell Number A cell suspension looks cChapter-7-Microbial-Growth-and-Growth-control-微生物学-教学课件-英文版 A continuous culture is essentially a flow system of constant volume to which medi
24、um is added continuously and from which continuous removal of any overflow can occur.Once such a system is in equilibrium,cell number and nutrient status remain constant,and the system is said to be in steady state.7.4 Continuous Culture:The Chemostat A continuous culture is es The most common type
25、of continuous culture device used is a chemostat,which permits control of both the population density and the growth rate of the culture.Both parameters can be set by the experimenter.The Chemostat The most common type of coChemostat used for continuous cultures.Rate of growth can be controlled eith
26、er by controlling the rate at which new medium enters the growth chamber or by limiting a required growth factor in the medium.Chemostat used for continuous Relationship among nutrient concentration,growth rate(solid line),and growth yield(dashed line)in a batch culture(closed system).At low nutrien
27、t concentrations both growth rate and growth yield are affected.Relationship among nutrient coSteady-state relationships in the chemostat.The dilution rate is determined from the flow rate and the volume of the culture vessel.Thus,with a vessel of 1000ml and a flow rate through the vessel of 500ml/h
28、r,the dilution rate would be 0.5hr-1.Note that at high dilution rates,growth cannot balance dilution,and the population washes out.Note also that although the population density remains constant during steady state,the growth rate(doubling time)can vary over a wide range.Thus,the experimenter can ob
29、tain populations with widely varying growth rates without affecting population density.Steady-state relationships in Even over rather wide ranges,any desired growth rate can be obtained in the chemostat by simply varying the dilution rate.A practical advantage to the chemostat is that a population m
30、ay be maintained in the exponential growth phase for long periods,for days and even weeks.The experimenter using the chemostat can have such cells available at any time.Experimental Uses of the ChemostatEven over rather wide ranges,The activities of microorganisms are greatly affected by the chemica
31、l and physical conditions of their environments.Understanding environmental in fluences helps us to explain the distribution of microorganisms in nature and makes it possible for us to devise methods for controlling microbial activities and destroying undesirable organisms.Four main factors:Temperat
32、ure,pH,water availability,and oxygen.7.5 Effect of Environment on GrowthThe activities of microorganis Bacteria grow over a range of temperatures;they do not reproduce below the minimum growth temperattire nor above the maximum growth temperature.Within the temperature growth range there is an optim
33、um growth temperature at which bacterial reproduction is fastest.Effect of temperature on bacterial growth rate Bacteria grow over a range of Enzymes exhibit a Q10 so that within a suitable temperature range the rate of enzyme activity doubles for every 10 C rise in temperature.Enzymes exhibit a Q10
34、 so t Microorganisms are classified as psychrophiles,mesophiles.thermophiles,and extremethemophiles based on their optimal growth temperature.Microorganisms are classifiedEffect of oxygen concentration on the growth of various bacteria in tubes of solid medium.(a)Obligate aerobes-growth occurs only
35、in the short distance to which the oxygen diffuses into the medium.(b)Facultative anaerobes growth is best near the surface,where oxygen is available,but occurs throughout the tube.(c)Obligate anaerobes-oxygen is toxic,and there is no growth near the surface.(d)Aerotolerant anaerobes-growth occurs e
36、venly throughout the tube but is not better at the surface because the organisms do not use oxygen.(e)Microaerophiles,aerobic organisms that do not tolerate atmospheric concentrations of oxygen-growth occurs only in a narrow band of optimal oxygen concentrationEffect of oxygen concentrationBacteria
37、Neutral conditionFungi Acidic conditionActinomycetes Alkaline conditionBacteria NeThe water activity of a solution is 1/100 the relative humidity of the solution(when expressed as a percent),or it is equivalent to the ratio of the solutions vapor pressure to that of pure water.Water activityThe wate
38、r activity of a solutiaw=P solution/P waterApproximate lower aw limits for microbial growth:0.90 1.00 for most bacteria,most algae and some fungi as Basidiomycetes,Mucor,Rhizopus.0.75 for Halobacterium,Aspergillus 0.60 for some saccharomyces speciesaw=P solution/P waterAppro If the concentration of
39、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 cellPlasmolyzed cellWater activity If the concentration of s7.6 Growt
40、h ControlDefinitions:Sterilization the process of destroying all forms of microbial life on an object or in a material.Disinfection the process of destroying vegetative pathogens but not necessary endospores.Antisepsis chemical disinfection of skin,mucous membranes or other living tissues7.6 Growth
41、ControlDefinitionMany antibiotics active against prokaryotes are also produced by prokaryotes.Include the aminoglycosides,the macrolides,and the tetracyclines.Many of these antibiotics have major clinical applications.The tetracyclines and the-lactam antibiotics are the two most important groups of
42、antibiotics in the medical field.Many antibiotics active againsContain amino sugars bonded by glycosidic linkage to other amino sugars.Inhibiting protein synthesis at the 30S subunit of the ribosome.Including streptomycin and its relatives,kanamycin,gentamicin,and neomycin,are used clinically agains
43、t gram-negative Bacteria.Aminoglycoside antibioticsStructure of kanamycin,an aminoglycoside antibiotic,an aminoglycoside antibiotic.The site of modification by an N-acetyltransferase,encoded by a resistance plasmid,is indicated.Contain amino sugars bonded byContain large lactone rings connected to s
44、ugar moieties.Include erythromycin,oleandomycin,spiramycin,and tylosin.Acts as a protein synthesis inhibitor at the level of the 50S subunit of the ribosome.Macrolide antibioticsStructure of erythromycin,a typical macrolide antibiotic.Contain large lactone rings coThe tetracyclines inhibiting almost
45、 all gram-positive and gram-negative Bacteria.Tetracycline is a protein synthesis inhibitor.It interferes with 30S ribosomal subunit function.TetracyclinesStructure of tetracycline and important derivatives.The tetracyclines inhibiting aViruses actually use the host cell machinery to perform their m
46、etabolic functions.Therefore,most attempts at chemical control of viruses result in toxicity for the host.Several agents are more toxic for the virus than the host,and there are a few agents produced by the host that specifically target viruses.There are several classes of chemotherapeutic agents th
47、at have been shown to be clinically effective in controlling viral replication.7.7 Viral ControlViruses actually use the host The most successful and commonly used agents for antiviral chemotherapy are the nucleoside analogs.The first compound to gain universal acceptance in this category was azidot
48、hymidine(AZT),Azidothymidine is chemically related to thymidine but is a dideoxy derivative,AZT inhibits HIV.Because the normal host cell function of DNA replication is targeted,these drugs almost always exhibit some level of host toxicity.Several other chemicals work at the level of viral polymeras
49、e.A relatively novel class of antiviral drugs are the protease inhibitors.Antiviral Chemotherapeutic AgentsThe most successful and commonAntiviral chemotherapeutic compoundsAntiviral chemotherapeutic comInterferons are antiviral substances produced by many animal cells in response to infection by ce
50、rtain viruses.They are low-molecular-weight proteins(17,000 MW)that prevent viral multiplication in normal cells by stimulating the production of antiviral proteins.There are three molecular types,IFN-,produced by leukocytes;IFN-,produced by fibroblnsts;and IFN-,produced by immune cells known as lym