《环境工程微生物学》课程教学资源（微生物学教案）原核微生物 A survey of prokaryotic cells and microorganisms.doc_大学文库

3. Distinguish among the types of external cell appendages.Bacteria often bear accessory appendages sprouting from their surfaces. Appendages canbe divided into two major groups: those that provide motility (flagella and axial filaments)andthosethatprovide attachments orchannels(fimbriaeandpili)4. Describe the structure and position of bacterial flagella and axial filaments, and theirattachmentpatterns.Flagella provide the power of motility or self-propulsion. This allows a cell to swimfreely through an aqueous habitat. The bacterial flagellum displays three distinct parts: thefilament, the hook (sheath),and the basal body.Flagella vary both in number andarrangement according to twogeneral patterns: (1)In a polar arrangement, the fl agellaare attached atone or both endsof thecell.Three subtypes of this pattern are:monotrichous with a singleflagellum;lophotrichous with small bunches or tufts offlagella emerging from the same site,and amphitrichous with flagella at both poles ofthe cell.(2) In a peritrichous * arrangement, flagella are dispersed randomly over thesurfaceofthecell.The periplasmicflagella oraxial filaments.Aperiplasmicflagellum isatype of internalflagellum that is enclosed in the space between the outer sheath and the cell wallpeptidoglycan. The filaments curl closely around the spirochete coils yet are free tocontractand imparta twisting orflexingmotion to thecell.Thisformoflocomotion mustbe seen in live cells such as thespirocheteof syphilistobetrulyappreciated5.Discuss the structure and functions of pili and fimbriaeThe structures termedfimbria and pilus bothrefertobacterial surface appendages thatare involved in interactions with other cells but do not provide locomotion, except forsomespecialized pili.Fimbriae are small, bristlelikefi bers emerging fromthe surface of many bacterial cells.Their exact composition varies, but most of them contain protein.Fimbriae have aninherent tendencytostick toeach other and tosurfaces.Theymayberesponsibleforthemutual clinging of cells that leads to biofilms and other thick aggregates of cells on thesurface of liquids and for the microbial colonization of inanimate solids such as rocksandglass.Apilus (also called a sex pilus)is an elongate, rigid tubular structure made ofa specialprotein, pilin.So far, true pili have been found only on gram-negative bacteria, wherethey are utilized primarily in a“mating”process between cells called conjugation,which involves a transfer of DNA from one cell to another.6.Define glycocalyx, and describe its different forms and functions.Thebacterial cell surface isfrequently exposedto severeenvironmental conditions.Theglycocalyx develops as a coating of macromolecules to protect the cell and, in some cases,help it adhere to its environment Glycocalyces differ among bacteria in thickness,organization,and chemical composition.Somebacteria arecovered with a loose shield calleda slime layer that evidently protects them from dehydration and loss of nutrients.Otherbacteria produce capsules composed ofrepeating polysaccharide units, of protein, or of both.2

2 3. Distinguish among the types of external cell appendages. Bacteria often bear accessory appendages sprouting from their surfaces. Appendages can be divided into two major groups: those that provide motility (flagella and axial filaments) and those that provide attachments or channels (fimbriae and pili). 4. Describe the structure and position of bacterial flagella and axial filaments, and their attachment patterns. Flagella provide the power of motility or self-propulsion. This allows a cell to swim freely through an aqueous habitat. The bacterial flagellum displays three distinct parts: the filament, the hook (sheath), and the basal body. Flagella vary both in number and arrangement according to two general patterns: (1) In a polar arrangement, the fl agella are attached at one or both ends of the cell. Three subtypes of this pattern are: monotrichous with a single flagellum; lophotrichous with small bunches or tufts of flagella emerging from the same site; and amphitrichous with flagella at both poles of the cell. (2) In a peritrichous * arrangement, flagella are dispersed randomly over the surface of the cell. The periplasmic flagella or axial filaments. A periplasmic flagellum is a type of internal fl agellum that is enclosed in the space between the outer sheath and the cell wall peptidoglycan. The filaments curl closely around the spirochete coils yet are free to contract and impart a twisting or flexing motion to the cell. This form of locomotion must be seen in live cells such as the spirochete of syphilis to be truly appreciated 5. Discuss the structure and functions of pili and fimbriae. The structures termed fimbria and pilus both refer to bacterial surface appendages that are involved in interactions with other cells but do not provide locomotion, except for some specialized pili. Fimbriae are small, bristlelike fi bers emerging from the surface of many bacterial cells. Their exact composition varies, but most of them contain protein. Fimbriae have an inherent tendency to stick to each other and to surfaces. They may be responsible for the mutual clinging of cells that leads to biofilms and other thick aggregates of cells on the surface of liquids and for the microbial colonization of inanimate solids such as rocks and glass. A pilus (also called a sex pilus) is an elongate, rigid tubular structure made of a special protein, pilin . So far, true pili have been found only on gram-negative bacteria, where they are utilized primarily in a “mating” process between cells called conjugation, which involves a transfer of DNA from one cell to another. 6. Define glycocalyx, and describe its different forms and functions. The bacterial cell surface is frequently exposed to severe environmental conditions. The glycocalyx develops as a coating of macromolecules to protect the cell and, in some cases, help it adhere to its environment. Glycocalyces differ among bacteria in thickness, organization, and chemical composition. Some bacteria are covered with a loose shield called a slime layer that evidently protects them from dehydration and loss of nutrients. Other bacteria produce capsules composed of repeating polysaccharide units, of protein, or of both

4.3The cell envelope: the boundary layer of bacteria.1.Explain the concept of the cell envelope, and describe its structureThe majority of bacteriahavea chemicallycomplex external coveringtermed the cellenvelopethat lies outside of the cytoplasm.It is composed of twomain layers:the cell walland the cell membrane.These layers are stacked together and often tightlybound into a unitlike the outer husk and casings of a coconut. Although each envelope layer performs adistinct function, together they act as a single unit that maintains cell integrity.2. Outline the structure andfunctions ofcell walls,and explain the role of peptidoglycanIn general, the cell wall helps determine the shape of a bacterium, and it also provides thekind of strong structural support necessary to keep a bacterium from bursting or collapsingbecause of changes in osmotic pressure.The cell walls of most bacteria gain their relativestrength and stability from a unique macromolecule called peptidoglycan (PG).Thiscompound is composed of a repeating framework of long glycan chains cross-linked byshort peptide fragments.The amount and exact composition of peptidoglycan vary amongthemajorbacterialgroups3. Contrast the major structure of gram-positive and gramnegative cell walls.The bulk of the gram-positive cell wall is a thick, homogeneous sheath of peptidoglycanrangingfrom20 to80nm in thickness.Italsocontains tightlybound acidicpolysaccharidesincluding teichoic acid directly attached to the peptidoglycan and lipoteichoic acid. Cellwall teichoic acid is a polymer of ribitol or glycerol and phosphate embedded in thepeptidoglycan sheath. Lipoteichoic acid is similar in structure but is attached to the lipids inthe plasma membrane.These molecules appear to function in cell wall maintenance andenlargement during cell division. They also move cations into and out of the cell andstimulate a specific immune response.The cell wall of gram-positivebacteria is oftenpressed tightly against the cell membrane with very little space between them, but in somecells, a thin periplasmic space is evident between the cell membrane and cell wall.Thegram-negativecell wall ismore complex inmorphologybecauseit is composed ofan outermembrane(OM)andathinner shell ofpeptidoglycan.Theoutermembraneissomewhat similar in construction to the cell membrane,except that it contains specializedtypes of lipopolysaccharides(LPS)and lipoproteins.Lipopolysaccharides are composedof lipid molecules bound to polysaccharides.The lipids form thematrix ofthetoplayer ofthe OM, and thepolysaccharide strands project from the lipid surface.The lipid portionmay become toxic when it is released during infections. The polysaccharides give rise tothe somatic(O)antigen in gram-negative pathogens and can beused in identification.Theymayalso function as receptors and in blocking host defenses.Twotypes of proteins arelocated in the OM. The porins are inserted in the upper layer of the outer membrane. Theyhave some regulatory control overmolecules entering and leaving the cell.Many qualitiesof the selective permeability of gram-negative bacteria tobile, disinfectants, and drugs aredue to the porins. Some structural proteins are also embedded in the upper layer of the OM.Thebottomlayerof theoutermembraneis similartothecell membraneinitsoverallstructure and is composed of phospholipids and lipoproteins. There is a well-developed3

3 4.3 The cell envelope: the boundary layer of bacteria. 1. Explain the concept of the cell envelope, and describe its structure. The majority of bacteria have a chemically complex external covering, termed the cell envelope that lies outside of the cytoplasm. It is composed of two main layers: the cell wall and the cell membrane. These layers are stacked together and often tightly bound into a unit like the outer husk and casings of a coconut. Although each envelope layer performs a distinct function, together they act as a single unit that maintains cell integrity. 2. Outline the structure and functions of cell walls, and explain the role of peptidoglycan. In general, the cell wall helps determine the shape of a bacterium, and it also provides the kind of strong structural support necessary to keep a bacterium from bursting or collapsing because of changes in osmotic pressure. The cell walls of most bacteria gain their relative strength and stability from a unique macromolecule called peptidoglycan (PG). This compound is composed of a repeating framework of long glycan chains cross-linked by short peptide fragments. The amount and exact composition of peptidoglycan vary among the major bacterial groups. 3. Contrast the major structure of gram-positive and gramnegative cell walls. The bulk of the gram-positive cell wall is a thick, homogeneous sheath of peptidoglycan ranging from 20 to 80 nm in thickness. It also contains tightly bound acidic polysaccharides, including teichoic acid directly attached to the peptidoglycan and lipoteichoic acid. Cell wall teichoic acid is a polymer of ribitol or glycerol and phosphate embedded in the peptidoglycan sheath. Lipoteichoic acid is similar in structure but is attached to the lipids in the plasma membrane. These molecules appear to function in cell wall maintenance and enlargement during cell division. They also move cations into and out of the cell and stimulate a specific immune response. The cell wall of gram-positive bacteria is often pressed tightly against the cell membrane with very little space between them, but in some cells, a thin periplasmic space is evident between the cell membrane and cell wall. The gram-negative cell wall is more complex in morphology because it is composed of an outer membrane (OM) and a thinner shell of peptidoglycan. The outer membrane is somewhat similar in construction to the cell membrane, except that it contains specialized types of lipopolysaccharides (LPS) and lipoproteins. Lipopolysaccharides are composed of lipid molecules bound to polysaccharides. The lipids form the matrix of the top layer of the OM, and the polysaccharide strands project from the lipid surface. The lipid portion may become toxic when it is released during infections. The polysaccharides give rise to the somatic (O) antigen in gram-negative pathogens and can be used in identification. They may also function as receptors and in blocking host defenses. Two types of proteins are located in the OM. The porins are inserted in the upper layer of the outer membrane. They have some regulatory control over molecules entering and leaving the cell. Many qualities of the selective permeability of gram-negative bacteria to bile, disinfectants, and drugs are due to the porins. Some structural proteins are also embedded in the upper layer of the OM. The bottom layer of the outer membrane is similar to the cell membrane in its overall structure and is composed of phospholipids and lipoproteins. There is a well-developed

periplasmic space above and below the peptidoglycan.This space is an importantreactionsite for a large and varied pool of substances that enter and leave the cell.TABLE 4.1Comparisonof Gram-PositiveandGram-Negative Cell WallsCharacteristicGram-PositiveGram-NegativeOneTwoNumberof major layersPeptidoglycanChemical compositionLipopolysaccharide (LPS)Teichoic acidLipoproteinLipoteichoic acidPeptidoglycanMycolic acids andPorin proteinspolysaccharides*Overall thicknessThicker (20-80 nm)Thinner (8-11 nm)NoYesOutermembraneNarrowExtensivePeriplasmicspacePermeabilitytomoleculesMorepenetrableLess penetrable4.Relate the characteristics ofother types ofcell walls and wall-freecells.Several bacterial groups lack the cell wall structure of gram-positive or gram-negativebacteria, and somebacteria haveno cell wall at all.Although theseexceptional forms can stainpositive or negative in the Gram stain, examination of their fine structure and chemistry showsthat they do not fit the descriptions for typical gram-negative or positive cells.5. Describe the structure of the cell membrane, and explain several ofits major roles in bacterialcells.Appearing just beneath the cell wall is the cell, or cytoplasmic, membrane, a very thin (5 -10nm),flexible sheetmolded completelyaroundthecytoplasm.Ingeneralcomposition,itisalipid bilayer with proteins embedded to vary ing degrees. In some locations, the cell membraneforms internal folds in the cytoplasm called mesosomes.These areprominent in gram-positivebacteria but are harder to see in gram-negative bacteria because of their relatively small sizeThe cell membraneprovidesa siteforenergy reactions,nutrientprocessing,andsynthesis.1.4Bacterial internalstructure.1.Listthecontentsofthecell cytoplasmThe cell membrane surrounds a complex solution referred to as cytoplasm, or cytoplasmicmatrix.This chemical“pool"is aprominent siteformanyof the cell'sbiochemical andsynthetic activities. Its major component is water (70%-80%), which serves as a solventfor a complex mixture of nutrients including sugars, amino acids, and other organicmoleculesand salts.The components of this pool serveasbuildingblocksforcell synthesisor as sources of energy.The cytoplasm also holds larger, discrete bodies such as thechromosome, ribosomes, granules, and actin strands.2.Describefeaturesof the bacterial chromosomeandplasmids.The hereditary material of most bacteria exists in the form of a single circular strand of4

4 periplasmic space above and below the peptidoglycan. This space is an important reaction site for a large and varied pool of substances that enter and leave the cell. 4. Relate the characteristics of other types of cell walls and wall-free cells. Several bacterial groups lack the cell wall structure of gram-positive or gram-negative bacteria, and some bacteria have no cell wall at all. Although these exceptional forms can stain positive or negative in the Gram stain, examination of their fine structure and chemistry shows that they do not fi t the descriptions for typical gram-negative or positive cells. 5. Describe the structure of the cell membrane, and explain several of its major roles in bacterial cells. Appearing just beneath the cell wall is the cell, or cytoplasmic, membrane, a very thin (5– 10 nm), flexible sheet molded completely around the cytoplasm. In general composition, it is a lipid bilayer with proteins embedded to varying degrees. In some locations, the cell membrane forms internal folds in the cytoplasm called mesosomes. These are prominent in gram-positive bacteria but are harder to see in gram-negative bacteria because of their relatively small size. The cell membrane provides a site for energy reactions, nutrient processing, and synthesis. 1.4 Bacterial internal structure. 1. List the contents of the cell cytoplasm. The cell membrane surrounds a complex solution referred to as cytoplasm, or cytoplasmic matrix. This chemical “pool” is a prominent site for many of the cell’s biochemical and synthetic activities. Its major component is water (70%–80%), which serves as a solvent for a complex mixture of nutrients including sugars, amino acids, and other organic molecules and salts. The components of this pool serve as building blocks for cell synthesis or as sources of energy. The cytoplasm also holds larger, discrete bodies such as the chromosome, ribosomes, granules, and actin strands. 2. Describe features of the bacterial chromosome and plasmids. The hereditary material of most bacteria exists in the form of a single circular strand of

DNA designated as thebacterial chromosome.Although the chromosome is the minimalgenetic requirement for bacterial survival, many bacteria contain other, nonessential piecesof DNAcalledplasmids.Thesetiny strands existapartfromthechromosome,although attimes they can become integrated into it.Duringbacterial reproduction,they are duplicatedandpassedontooffspring.Theyarenot essential to bacterial growthandmetabolism,buttheyoften conferprotectivetraits suchas resisting drugs and producingtoxins and enzymesBecause they can be readily manipulated in the laboratory and transferred from onebacterial cell to another,plasmids are an important agent in modern genetic engineeringtechniques.3.Characterizethebacterial ribosomes and cytoskeletonA bacterial cell contains thousands of ribosomes, which are made of RNA and proteinWhen viewed even by very high magnification, ribosomes show up as fine, sphericalspecks dispersed throughout the cytoplasm that often occur in chains (polysomes).Manyarealso attachedtothecell membrane.Chemically,a ribosome isacombination ofaspecialtypeofRNAcalled ribosomalRNA,orrRNA(about60%),andprotein(40%)4.Describe inclusion bodies and granules,andexplaintheirimportanceto cells.Most bacteria are exposed to severe shifts in the availability of food. During periods ofnutrient abundance, some can compensate by storing nutrients as inclusion bodies,orinclusions, of varying size,number,and content As theenvironmental source of thesenutrients becomes depleted, the bacterial cell canmobilize its own storehouse as required.Some inclusion bodies contain condensed, energy-rich organic substances, such asglycogen and poly b-hydroxybutyrate (PHB), within special single-layered membranes. Aunique type of inclusion found in some aquatic bacteria is gas vesicles that providebuoyancy and flotation.Otherinclusions,also calledgranules, contain crystalsof inorganiccompoundsandare notenclosed bymembranes5.Describe the life cycle of endospore-forming bacteria including the fomation andgerminationofendospores.These bacteria have a two-phase life cycle that shifts between a vegetative cell and anendospore. The vegetative cell is the metabolically active and growing phase. Whenexposed to certain environmental signals,itforms an endosporeby a process termedsporulation.The spore exists in an inert, resting condition that is capable of high resistanceandverylong-term survival.6.Discusstheresistanceand significanceofendospores.Bacterial endospores are the hardiest of all life forms, capable of withstanding extremes inheat, drying,freezing,radiation, and chemicals that would readily kill ordinary cells.Although themajorityof spore-formingbacteria are relativelyharmless, several bacterialpathogens are sporeformers. In fact, some aspects of the diseases they cause are related tothe persistence andresistanceoftheir spores.Hospitals and clinicsmust takeprecautionstoguard againstthepotential harmful effectsof endospores in wounds.Endospore destruction is aparticular concern of the5

5 DNA designated as the bacterial chromosome. Although the chromosome is the minimal genetic requirement for bacterial survival, many bacteria contain other, nonessential pieces of DNA called plasmids. These tiny strands exist apart from the chromosome, although at times they can become integrated into it. During bacterial reproduction, they are duplicated and passed on to offspring. They are not essential to bacterial growth and metabolism, but they often confer protective traits such as resisting drugs and producing toxins and enzymes. Because they can be readily manipulated in the laboratory and transferred from one bacterial cell to another, plasmids are an important agent in modern genetic engineering techniques. 3. Characterize the bacterial ribosomes and cytoskeleton. A bacterial cell contains thousands of ribosomes, which are made of RNA and protein. When viewed even by very high magnification, ribosomes show up as fine, spherical specks dispersed throughout the cytoplasm that often occur in chains (polysomes). Many are also attached to the cell membrane. Chemically, a ribosome is a combination of a special type of RNA called ribosomal RNA, or rRNA (about 60%), and protein (40%). 4. Describe inclusion bodies and granules, and explain their importance to cells. Most bacteria are exposed to severe shifts in the availability of food. During periods of nutrient abundance, some can compensate by storing nutrients as inclusion bodies, or inclusions, of varying size, number, and content. As the environmental source of these nutrients becomes depleted, the bacterial cell can mobilize its own storehouse as required. Some inclusion bodies contain condensed, energy-rich organic substances, such as glycogen and poly b-hydroxybutyrate (PHB), within special single-layered membranes. A unique type of inclusion found in some aquatic bacteria is gas vesicles that provide buoyancy and flotation. Other inclusions, also called granules, contain crystals of inorganic compounds and are not enclosed by membranes. 5. Describe the life cycle of endospore-forming bacteria, including the formation and germination of endospores. These bacteria have a two-phase life cycle that shifts between a vegetative cell and an endospore. The vegetative cell is the metabolically active and growing phase. When exposed to certain environmental signals, it forms an endospore by a process termed sporulation. The spore exists in an inert, resting condition that is capable of high resistance and very long-term survival. 6. Discuss the resistance and significance of endospores. Bacterial endospores are the hardiest of all life forms, capable of withstanding extremes in heat, drying, freezing, radiation, and chemicals that would readily kill ordinary cells. Although the majority of spore-forming bacteria are relatively harmless, several bacterial pathogens are sporeformers. In fact, some aspects of the diseases they cause are related to the persistence and resistance of their spores. Hospitals and clinics must take precautions to guard against the potential harmful effects of endospores in wounds. Endospore destruction is a particular concern of the

food-canning industry. Several endospore-forming species cause food spoilage orpoisoning. Ordinary boiling (1oo° C) will usually not destroy such spores, so canning iscarried out in pressurized steam at 120°C for 20 to 30 minutes. Such rigorous conditionswill ensure that thefood is sterile and free from viable bacteria.4.5 Bacterial shapes, arrangement and sizes.1.Describethe shapes of bacteria and their possiblevariants.Bacteria exhibit considerable variety in shape, size, and colonial arrangement. It isconvenient to describe most bacteria by one of three general shapes as dictated by theconfiguration of the cell wall.If the cell is spherical or ball-shaped, the bacterium isdescribed as a coccus.Cocci can be perfect spheres, but they also can exist as oval,bean-shaped, or even pointed variants. A cell that is cylindrical (longer than wide) is termeda rod or bacillus.Thereis also a genus named Bacillus.As mightbeexpected,rodsarealso quite varied in their actual form Depending on the bacterial species, they can beblocky,spindle-shaped, roundended, long and threadlike (filamentous),or even clubbed ordrumstick-shaped.When a rod is short and plump,it is called a coccobacillus; if it is gentlycurved, it is a vibrio. A bacterium having the shape of a curviform or spiralshaped cylinderis called a spirillum, a rigid helix, twisted twice or more along its axis (like a corkscrew)2. Identify several arrangements of bacteria and how they are formed.Bacterial cells can also be categorized according to arrangement, or style of groupingThemain factors influencing the arrangement of a particular cell type are its pattern ofdivision and how the cells remain attached afterward. The greatest variety in arrangementoccurs in cocci.They may exist as singles, in pairs (diplococci),in tetrads (groups offour),in irregular clusters (both staphylococci *and micrococci),or in chains of a fewtohundreds of cells(streptococci).3. Indicate the size ranges in bacteria in comparison to other organisms.Thesizes of bacteriarangefromthose just barelyvisiblewithlightmicroscopy(O.2m)tothosemeasuringa thousand times that size.Coccimeasureanywherefrom 0.5to3.0μmindiameter:bacillirangefrom0.2to2.0μmindiameterandfrom0.5to20μminlength.4.6 Classification systems of prokaryotic domains: archaea and bacteria1.Describe the purposes ofclassification and taxonomy in the study ofprokaryotesClassifi cation systems serve bothpractical and academic purposes.They aid indifferentiating and identifying unknown species in medical and applied microbiology.Theyare also useful in organizing bacteria and as a means of studying their relationships andevolutionaryorigins.2.Overview characteristics used to classify bacteriaThe methods that a microbiologist uses to identify bacteria to the level of genusand species fall into the main categories of morphology (microscopic and macroscopic),bacterial physiology or biochemistry, serological analysis, and genetic techniques.Data from6

6 food-canning industry. Several endospore-forming species cause food spoilage or poisoning. Ordinary boiling (100°C) will usually not destroy such spores, so canning is carried out in pressurized steam at 120°C for 20 to 30 minutes. Such rigorous conditions will ensure that the food is sterile and free from viable bacteria. 4.5 Bacterial shapes, arrangement and sizes. 1. Describe the shapes of bacteria and their possible variants. Bacteria exhibit considerable variety in shape, size, and colonial arrangement. It is convenient to describe most bacteria by one of three general shapes as dictated by the configuration of the cell wall. If the cell is spherical or ball-shaped, the bacterium is described as a coccus. Cocci can be perfect spheres, but they also can exist as oval, bean-shaped, or even pointed variants. A cell that is cylindrical (longer than wide) is termed a rod, or bacillus. There is also a genus named Bacillus. As might be expected, rods are also quite varied in their actual form. Depending on the bacterial species, they can be blocky, spindle-shaped, roundended, long and threadlike (filamentous), or even clubbed or drumstick-shaped. When a rod is short and plump, it is called a coccobacillus; if it is gently curved, it is a vibrio. A bacterium having the shape of a curviform or spiralshaped cylinder is called a spirillum, a rigid helix, twisted twice or more along its axis (like a corkscrew). 2. Identify several arrangements of bacteria and how they are formed. Bacterial cells can also be categorized according to arrangement, or style of grouping. The main factors influencing the arrangement of a particular cell type are its pattern of division and how the cells remain attached afterward. The greatest variety in arrangement occurs in cocci. They may exist as singles, in pairs ( diplococci), in tetrads (groups of four), in irregular clusters (both staphylococci * and micrococci ) , or in chains of a few to hundreds of cells ( streptococci ). 3. Indicate the size ranges in bacteria in comparison to other organisms. The sizes of bacteria range from those just barely visible with light microscopy (0.2 μ m) to those measuring a thousand times that size. Cocci measure anywhere from 0.5 to 3.0 μm in diameter; bacilli range from 0.2 to 2.0 μm in diameter and from 0.5 to 20 μm in length. 4.6 Classification systems of prokaryotic domains: archaea and bacteria 1. Describe the purposes of classification and taxonomy in the study of prokaryotes. Classifi cation systems serve both practical and academic purposes. They aid in differentiating and identifying unknown species in medical and applied microbiology. They are also useful in organizing bacteria and as a means of studying their relationships and evolutionary origins. 2. Overview characteristics used to classify bacteria. The methods that a microbiologist uses to identify bacteria to the level of genus and species fall into the main categories of morphology (microscopic and macroscopic), bacterial physiology or biochemistry, serological analysis, and genetic techniques. Data from

a cross section of such tests can produce a unique profile of each bacterium.Finaldifferentiation of any unknown species is accomplished by comparing its profile with thecharacteristics of known bacteria in tables, charts, and keys.4.7 Survey of Prokaryotic Groups with Unusual Characteristics1.Differentiatevarious groupsofphotosynthetic bacteria.Photosynthetic bacteria are independent cells that contain special light-trapping pigmentsand can use the energy of sunlight to synthesize all required nutrients from simple inorganiccompounds. The two general types of photosynthetic bacteria are those that produce oxygenduringphotosynthesis and thosethat produce some other substance, such as sulfur granulesor sulfates.The cyanobacteria are indeed bacteria with a gram-negative cell wall and generalprokaryoticstructure.Thesebacteriarangeinsizefrom1μmto1oμm,and theycanbeunicellular or can occur in colonial or filamentous groupings Cyanobacteria are among theoldest types of bacteria on earth.Cyanobacteria arevery widely distributed in nature.Theygrow profusely in freshwater and seawater and are thought to beresponsible for periodicblooms thatkill off fi sh. Somemembers are so pollution-resistant thatthey serve asbiologicalindicatorsofpollutedwater.The green and purple bacteria are also photosynthetic and contain pigments.They differfrom thecyanobacteria in having adifferenttypeof chlorophyll called bacteriochlorophylland by not giving off oxygen as a product of photosynthesis. They live in sulfur springs,freshwaterlakes,and swampsthat aredeep enoughfortheanaerobic conditionstheyrequireyet where their pigment can still absorb wavelengths of light.2. Describe bacteria with extremes in size.In1985,biologists discovered a newbacterium living in the intestine of surgeonfish that atthe time was a candidate for the Guinness Book of World Records. The large cells, namedEpulopiscium fishelsoni (“guest at a banquet of fish"), measure around 100 μm in length,althoughsomespecimenswereaslargeas300μm.At the other extreme, microbiologists are being asked to reevaluate the lower limits ofbacterial size.Up until now it has been generally accepted that the smallest cells on the planetare someform of mycoplasma withdimensions of 0.2to 0.3μm, which is right at the limit ofresolutionwith lightmicroscopes.Anew controversy isbrewing over thediscovery of tinycells that look likedwarf bacteria but are10times smallerthan mycoplasmas and100 timessmaller than the average bacterial cell3. Summarize the basic characteristics of archaea.Among the ways that the archaea differ signifi cantly from other cell types are that certaingenetic sequences are found only in their ribosomal RNA and that they have uniquemembrane lipidsand cell wall construction.It is clear that thearchaea arethemost primitiveof all lifeforms and have retained characteristics of the fi rst cells that originated on the earthnearly4billionyearsago4.CompareDomainArchaeawithDomainsBacteriaandEukarya.2

7 a cross section of such tests can produce a unique profile of each bacterium. Final differentiation of any unknown species is accomplished by comparing its profile with the characteristics of known bacteria in tables, charts, and keys. 4.7 Survey of Prokaryotic Groups with Unusual Characteristics 1. Differentiate various groups of photosynthetic bacteria. Photosynthetic bacteria are independent cells that contain special light-trapping pigments and can use the energy of sunlight to synthesize all required nutrients from simple inorganic compounds. The two general types of photosynthetic bacteria are those that produce oxygen during photosynthesis and those that produce some other substance, such as sulfur granules or sulfates. The cyanobacteria are indeed bacteria with a gram-negative cell wall and general prokaryotic structure. These bacteria range in size from 1 μm to 10 μm, and they can be unicellular or can occur in colonial or filamentous groupings. Cyanobacteria are among the oldest types of bacteria on earth. Cyanobacteria are very widely distributed in nature. They grow profusely in freshwater and seawater and are thought to be responsible for periodic blooms that kill off fi sh. Some members are so pollution-resistant that they serve as biological indicators of polluted water. The green and purple bacteria are also photosynthetic and contain pigments. They differ from the cyanobacteria in having a different type of chlorophyll called bacteriochlorophyll and by not giving off oxygen as a product of photosynthesis. They live in sulfur springs, freshwater lakes, and swamps that are deep enough for the anaerobic conditions they require yet where their pigment can still absorb wavelengths of light. 2. Describe bacteria with extremes in size. In 1985, biologists discovered a new bacterium living in the intestine of surgeonfish that at the time was a candidate for the Guinness Book of World Records. The large cells, named Epulopiscium fishelsoni (“guest at a banquet of fish”), measure around 100 m in length, although some specimens were as large as 300 m. At the other extreme, microbiologists are being asked to reevaluate the lower limits of bacterial size. Up until now it has been generally accepted that the smallest cells on the planet are some form of mycoplasma with dimensions of 0.2 to 0.3 m, which is right at the limit of resolution with light microscopes. A new controversy is brewing over the discovery of tiny cells that look like dwarf bacteria but are 10 times smaller than mycoplasmas and 100 times smaller than the average bacterial cell. 3. Summarize the basic characteristics of archaea. Among the ways that the archaea differ signifi cantly from other cell types are that certain genetic sequences are found only in their ribosomal RNA and that they have unique membrane lipids and cell wall construction. It is clear that the archaea are the most primitive of all life forms and have retained characteristics of the fi rst cells that originated on the earth nearly 4 billion years ago. 4. Compare Domain Archaea with Domains Bacteria and Eukarya

B.Prokaryotic cells lack the membrane-surrounded organellescausing fever and other signs and symptoms, incuding the onesand nuclear compartment ofeukaryotic clls but are stillthat were fatal for Mr. Jones.complex in their structure and function. All prokaryotes havea cell membrane, cytoplasm, ribosomes,and a chromosomeStaphylococcus aureus is the most common cause of endocar.C.Appendages: Somebactenahaveprojections thatextendditis, especially associated with artificial heart valves. MRSAstandsfrom the cell.for methicillin resistant Staphylococcus aureus, which is a short.1Flagella (and intemal axtalfilaments foundinhand way of saying that the microbe is resistant to numerousspirochetes) are used for motility.drugs used in treatment.The reason that the penicllin2.Fimbriae function in adhering totheevironment; pllMrjoneswasgiventotakeathomewouldnothaveworkedisprovide a means for genetic exchange.thatmtstranureusistantteatmnwith3helyocalymaybeasimelayroaapsulemixtureof drugs is indicated, but itneeds to start early in the in-4.3The Cell Envelope:The BoundaryLayerof Bacterlafection.MRSA isan emerging pathogen thatstartedas a problemA,Most prokaryotes are surrounded by a protective emvelopeinhospitalsbutisnowprominent innonhospitalsttings as wel.that consists of the cell wall and the cellmembraneThe wallisrelativelyrigiddueopeptidoglyanFot more background on MRSA and endocarditis, see chapter 18.C, Structural differences give rise to gram-positive and gram-negativecelis, as differentiated by the Gram stainI. Gram-positive bacteria contain a thick wall composedof peptidoglycan and teichoic acid in a single layer.Chapter Summary with2.Gram-negative bacteriahaveathinnertwolayercellKeyTermswall withanouermmaethinypepidoglycan,ada wel-deoped perplasmic spae3.Wall structure gives rise to differences in staining.4.1Basle Characteristics of Cells and Life Formstoxicity,and effects ofdrugs and disinfctanAAll living things are composed of cells, which are complex4.4 Bacterial Internal StructurecollectiosofmacromoleculesthatcayutfivingThe cell cytoplasm is a watery substance that hoids some or all ofprocesses All cells must have the minimum structure of anthe following internal structures in bacteria: the chromosome(s)Outellmmraylasmcomosom,acondnsedinthenuceod; riosoms,whchseeasthesierlbesomes.of protein synthesis and are 70S in size; extra genetic informationB. Cells can be divided into two basic types prokaryotes andin the form of plasmids, storage structures known as inclusions;eukaryotesacytoskeleonofbactealactin,whichhepsgivethProkaryticeisarethbascstuctununactbacterumitsshapandinsombacteaanendopore,whichadarahyckcsalleha highly resistant structure for survival, not reproduction.arehighlysuccessfuland adaptablesinglecellife4.5celhrnmnnforms.2.Eukaryotic cells containamembrane-suoundedAMost bacteria are unicellular and are found in a great varietyof shapes, arrangements, and sizes, General shapes includenuckeus and a number of organelles that function inspecific ways.A wide varicty of organisms, from singlecocc, bacill, and helical forms such as splilla andsproceSomsowgatriationithnthescelled protozoans to humans, are composed ofinshapeand sizeand areplemorphic.Othervariationseukaryotic cells.3Viresaeoyondelivingorcellsinclude coccobacill, vbrios, and filamentous forms.BProkaryotesdivideby binary fssion and donot utlizeely on host cells to replicateC.CelsshowthebasicessentialcharacteristicsoflifeParsmitosis.Various arrangements result from clldivisionandtcells and macromolecules do not show these characteristicsindependenty.and sarcina for cocci; bacilli may form pairs, chains, orHeredtyandReproduction: Celsmustpass ongeneticpallsades.aiammobacteriaciesaealletnasadinformation to their offspring, whether asexuully (withone parent) or sexually (with two parents).types.2Growth:Livingenttiesareabletogrowand increasein4.6 Classification Systems of the Prokaryotic Domains: Archaeasize,oftenrering and rebuilding themselves overtimand Bacteria3. Metabolism: This refers to the chemical reactions in theAAnimportanttaxonomicsystemisstandardizedby Benggy'cellcuingtsss onsoMauaf of Determinative Bacteriolog, which presentstheandthecaptureandrelease ofenergyusingATPprokaryotes in five major volumes.4,Responsiveness: Irritabtlty ts responsiveness toVolume I Domain Archaeaextemal stimuli, communicatlon is interaction withDomain Bacteria:Deeply Branching and Phototropicother cells, and motility originates from specialBacterialocomotor structures such as flagella and ciliaDomain BacteriaTransport:Nutrients must hebrought intothecellVolume 2 Proteobacteria (graim-negaitive cell walls)through the membrane and wastes expelled from the cell.Volume3 Low G +Cgram-positive Bacteris4.2ProkaryoticProfles:The Bacterla and ArchaeaVolume 4 High G + C gram-positive BacteriaPrkryensiswmgouacteridtVolumncomyepihesFoBctedetes, and Fusobacteria (gram-negative cell walls)archaea. Life on earth would not be possible without them.4.7 Survey of Prokaryotic Groups with Unusual CharacteristiesA.Several groups of bacteria have unusual adaptations and tifecycles.1. Medically important bacteria: Rickettsias andchlamydias are within the gram-negative group but areSmall obligateintracellular parasitesthat replicatewithin cells ofthe hosts they invade.2.Nonpathogenic bacterialgroupsThemajorityfbacterialspecies are free-living and not involved indisease. Unusual groups include photosynthetic bacteriasuch as cyanobacteria, which provide oxygen to theenvironment, and the green and purple bacteria.B.Archaea share many characteristics with bacteria but varyinceaingenetic aspects and structuressuchasthecell walland ribosomes.1. Many are adapted to extreme environments similar tothe earliest of earth's inhabitants.2.They are not considered medically important but are ofecological and potential economic importance.9