微生物学史微生物学史 (12).ppt

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1、Endospores-Sporulation&GerminationAfter learning this section,you should be able to:Describe in general terms the process of sporulation Describe the three stages that transform an endospore into an active vegetative cell Sporulation:Making Endospores Endospore-forming bacteria are common in soil,wh

2、ere they must be able to withstand fluctuating levels of nutrients.Sporulation(endospore formation)normally commences when growth ceases due to lack of nutrients.Thus it is a survival mechanism that allows the bacterium to produce a dormant cell that can survive until nutrients are again available a

3、nd vegetative growth can resume.These bacteria cycle between two states:vegetative growth and survival as an endospore.Vegetative growth is the normal,continuous cycle of growth and division.By contrast,sporulation is a complex process that occurs in a highly organized fashion over several hours.The

4、 mature endospore is located in a characteristic location in the mother cell(referred to as the sporangium),depending on the species of bacteria.Endospores may be centrally located,close to one end (subterminal),or terminal(figure 3.53).Sometimes an endospore is so large that it swells the sporangiu

5、m.One of the best-studied endospore formers is Bacillus subtilis,which is an important model organism.Sporulation may be divided into seven stages(as seen in the following picture).Endospore to Vegetative CellThe transformation of dormant spores into active vegetative cells is almost as complex as s

6、porulation.It occurs in three stages:(1)activation,(2)germination,and(3)outgrowth Activation is a process that prepares spores for germination and can result from treatments such as heating.This is followed by germination,the breaking of the spores dormant state.Germination begins when proteins call

7、ed germinant receptors,located in the inner membrane,detect small molecules such as sugars and amino acids.Upon detection of these molecules,a series of events occur,including release of the Ca-DPA complexes,breakdown of the peptidoglycan in the cortex,and water uptake.Eventually water levels inside

8、 the germinating spore reach those characteristic of vegetative cells and enzymes in the core become active.This allows the spore to begin synthesizing the various molecules it needs to initiate spore outgrowth and return to a vegetative state.Wordlist1.sporulation 芽孢形成芽孢形成2.mature endospore成熟的芽孢成熟的芽孢3.Sporangium 孢囊孢囊4.centrally located endospores 中生芽孢中生芽孢5.Subterminalendospores次端生芽孢次端生芽孢6.Terminal endospores端生芽孢端生芽孢7.swollen sporangium.芽孢膨大芽孢膨大8.Bacillus subtilis枯草芽孢杆菌枯草芽孢杆菌9.forespore septum 前芽孢隔板前芽孢隔板10.Engulfs吞没吞没 11.Bacillus megaterium巨大芽孢杆菌巨大芽孢杆菌12.Clostridium pectinovorum蚀果胶梭菌蚀果胶梭菌