微生物学史微生物学史 (33).ppt

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1、Influences of Environmental Factors on Microbial Growth After learning this section,you should be able toUse the terms that describe a microbes growth range or requirement for each of the factors that influence microbial growth.Describe the enzymes observed in microbes that protect them against toxi

2、c O2 products.Microbes are thought to be present nearly everywhere on Earth.Bacteria such as Bacillus infernus are able to live over 2.4 km below Earths surface,without oxygen and at temperatures above 60.Other microbes live at great ocean depths or in lakes such as the Great Salt Lake in Utah(USA)t

3、hat have high sodium chloride concentrations.Bacillus infernus,a hyper-thermophile,found 2.65-2.77 km beneath the Earths surface.Halobacterium salinarum Microorganisms that grow in such harsh conditions are called extremophiles.To extremophiles,the harsh conditions of their habitats are“normal”.Many

4、 other microbes are not extremophiles;they live in more moderate conditions.However,conditions can vary within any habitat,and microbes must be able to respond to any changes to ensure their survival.In this section,we briefly review the effects of the most important environmental factors on microbi

5、al growth.Major emphasis is given to pH,temperature,and oxygen level.pH pH is a measure of the relative acidity of a solution.Each species has a definite pH growth range and pH growth optimum.Acidophiles have their growth optimum between pH 0 and 5.5;Neutrophiles,between pH 5.5 and 8.0;Alkaliphiles(

6、alkalophiles),between pH 8.0 and 11.5.Alkaliphiles are distributed among all three domains of life.They include bacteria belonging to the genera Bacillus,Micrococcus,Pseudomonas,and Streptomyces;yeasts and filamentous fungi;and numerous archaea.In general,different microbial groups have characterist

7、ic pH preferences.Most known bacteria and protists are neutrophiles.Most fungi prefer more acidic surroundings,about pH 4 to 6;photosynthetic protists also seem to favor slight acidity.Many archaea are acidophiles.This picture shows that microbial habitats vary widely in pH-from pH 0 to 2 at the aci

8、dic end to alkaline lakes and soil with pH values between 9 and 10.A,archae;E,eukaryote;B,bacterium.TemperatureMicroorganisms are particularly susceptible to external temperatures because they cannot regulate their internal temperature.An important factor influencing the effect of temperature on gro

9、wth is the temperature sensitivity of enzyme-catalyzed reactions.High temperatures denature enzymes,transport carriers,and other proteins.Temperature also has a significant effect on microbial membranes.At very low temperatures,membranes solidify.At high temperatures,the lipid bilayer simply melts a

10、nd disintegrates.Thus when organisms are above or below their optimum temperature,both function and cell structure are affected.Cardinal temperaturesMicrobial growth has a characteristic temperature dependence with distinct cardinal temperatures.-minimum growth temperature-optimum growth temperature

11、-maximum growth temperatureThe cardinal temperatures vary greatly among microorganisms.Optima usually range from 0 to 75,whereas microbial growth occurs at temperatures extending from less than-20 to over l20.Some archaea even grow at 121,the temperature normally used in autoclaves.Microorganisms ar

12、e placed in different classes based on their temperature ranges for growth.They are ranked in order of increasing growth temperature range as psychrophiles,psychrotrophs,mesophiles,thermophiles,and hyperthermophiles.Representative ranges and optima for these five types are illustrated.Several terms

13、are used to describe microbes based on their temperature ranges for growth.Psychrophiles grow well at 0oC and have an optimum growth temperature of l5 oC;the maximum is around 20oC.Psychrotrophs(psychrotolerants)grow at 0oC or higher and typically have maxima at about 35oC.Mesophiles are microorgani

14、sms that grow in moderate temperatures.They have growth optima around 20 to 45 oC and often have a temperature minimum of 15 to 20oCand a maximum of about 45oC.Microorganisms are placed in different classes based on their temperature ranges for growth.They are ranked in order of increasing growth te

15、mperature range as psychrophiles,psychrotrophs,mesophiles,thermophiles,and hyperthermophiles.Representative ranges and optima for these five types are illustrated.Microbes that grow best at high temperatures are thermophiles and hyperthermophiles.Thermophiles grow at temperatures between 45 and 85oC

16、,and they often have optima between 55 and 65oC.Hyperthermophiles have growth optima between 85oC and about 113oC.They usually do not grow below 55oC.Oxygen ConcentrationThe importance of oxygen to the growth of an organism correlates with the processes it uses to conserve energy.Almost all multicel

17、lular organisms are completely dependent on atmospheric O2 for growth;that is,they are obligate aerobes.Microaerophiles are damaged by the normal atmospheric level of O2(20%)and require O2 levels in the range of 2 to 10%for growth.Facultative anaerobes do not require O2 for growth but grow better in

18、 its presence.In the presence of oxygen,they use O2 as the terminal electron acceptor during aerobic respiration.Aerotolerant anaerobes such as Enterococcus faecalis grow equally well whether O2 is present or not;they can tolerate O2,but they do not make use of it.Obligate anaerobes or Strict anaero

19、bes(e.g.,members of the genera Bacteroides,Clostridium,Methanococcus),O2 is toxic,and they are usually killed by the presence of O2.They cannot generate energy through aerobic respiration and employ other metabolic strategies such as fermentation or anaerobic respiration,neither of which requires O2

20、.Figure 7.13 Oxygen and Bacterial Growth.Each dot represents an individual bacterial colony within the agar or on its surface.The surface,which is directly exposed to atmospheric oxygen,is oxic.The oxygen content of the medium decreases with depth until the medium becomes anoxic toward the bottom of

21、 the tube.The presence and absence of the enzymes superoxide dismutase(SOD)and catalase for each type are shown.The nature of bacterial O2 responses can be readily determined by growing the bacteria in a solid culture medium or a medium such as thioglycollate broth,which contains a reducing agent to

22、 lower O2 levels.sThe different relationships with O2 are due to several factors,including the inactivation of proteins and the effect of toxic O2 derivatives.Effect of toxic O2 derivativesToxic O2 derivatives are formed when cellular proteins such as flavoproteins transfer electrons to O2.These tox

23、ic O2 derivatives are called reactive oxygen species(ROS),and they can damage proteins,lipids,and nucleic acids.ROS include the superoxide radical,hydrogen peroxide,and the most dangerous hydroxyl radical.A microorganism must be able to protect itself against ROS or it will be killed.Many microorgan

24、isms possess enzymes that protect against toxic O2 products.Obligate aerobes and facultative anaerobes usually contain the enzymes superoxide dismutase(SOD)and catalase,which catalyze the destruction of super-oxide radical and hydrogen peroxide,respectively.Peroxidase also can be used to destroy hyd

25、rogen peroxide.Wordlist1.Bacillus infernus 地狱芽孢杆菌2.sodium chloride NaCl3.extremophiles 极端微生物4.Acidophiles嗜酸微生物5.Neutrophils6.Alkaliphiles7.Denature 使变性8.cardinal temperatures 基本温度9.minimum,optimum,and maximum growth temperatures最小，最适，最高生长温度10.psychrophiles低温微生物，嗜冷微生物低温微生物，嗜冷微生物11.psychrotrophs 耐冷微生物

26、耐冷微生物12.Mesophiles嗜温微生物嗜温微生物13.Thermophiles 嗜热微生物嗜热微生物,14.hyperthermophiles 超超嗜热微生物嗜热微生物15.obligate aerobes专性好氧菌16.Microaerophiles微好氧菌微好氧菌17.Facultative anaerobes兼性厌氧菌兼性厌氧菌18.Aerotolerant anaerobes耐氧厌氧菌耐氧厌氧菌19.obligate anaerobes 专性厌氧菌，严格厌氧菌专性厌氧菌，严格厌氧菌20.thioglycollate巯基乙酸盐巯基乙酸盐21.derivative衍生物22.inactivation失活23.sulfhydryls巯基24.flavoproteins黄素蛋白25.reactive oxygen species(ROS)活性氧26.superoxide radical 超氧自由基 27.hydrogen peroxide 过氧化氢28.hydroxyl radical 羟基自由基29.superoxide dismutase(SOD)超氧化物歧化酶30.catalase,过氧化氢酶31.Peroxidase过氧化物酶