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Cell structure and function in BacteriaStructure and functionGrey reef sharkThe torpedo-like body of a shark is highly adapted for quick movement through water.typical bacterial cell structure Cell Shape and SizeCell morphologyHaloarcula-bacterium from aSalt pool in Sinai.Microorganisms really can besquare!Why?Yes,Bifidobacteria is Y-shaped.Cell morphologyMorphology and Biology Why a particular microbial cell evolved the morphology it has?Actually,we do not know why yet!Several selective forces are likely in play in setting the morphology of a given species:1.For nutrient uptake,High surface-to-volume ratios2.Movement,swimming or glidingAlthough we do not know why a particular microbial cell evolved it has,its morphology makes perfect sense in terms of fitness.This is an open question,maybe you can figure out this basic biological question！The shape of microbial cells is not related to evolutional relationship!90 mm0.01 mm(10 m)2 mmSingle cellMany cellspopulation-colonyMorphology of cell populationSize of Living ThingsBacteria:0.2m-over 700mLab rod-shaped strains 0.54mx15m Cell Shape and SizeThe significance of smallness Surface-to-volume ratio-Nutrient uptake rate metabolism rate Evolution:more cells more mutations more possibilities Haploid Diploid Space for essential biomolecules 0.15 m independent living cells 750 m Cell Shape and SizeA giant prokaryote,the surgeonfish symbiont:Epulopiscium fishelsoni 600 um long and 75 m wide with three eukaryote parameciumLarge body is supported by 100,000 or so copies of genome that meet the transcriptional and translational needs of the big cellsThe largest prokaryote,an oceanic bacterium,Thiomargarita namibiensis 400-750m wide.It is big,but it“cheats”because it is mostly vacuole.So,it has only one copy of genome.Very small bacteria(less than 1 m)such as many pathogenic bacteria have very small genome and lost many genes whose functions are supplied to them by their hostsCytoplasmic Membrane-structureRigidity of cytoplasmic membraneHopanoids(藿烷类化合物)in bacteriaLow-viscosity oil Cytoplasmic Membrane-structure Integral One-end inserted Peripheral Unevenly distributed functionally clusteredPeripheral proteins and their interactions with membrane Cytoplasmic Membrane-FunctionProton motive force Small hydrophobicMoleculesWater(aquaporin)Cytoplasmic Membrane-FunctionCytoplasmic Membrane-FunctionTransporters versus diffusionCharacteristics of Transport Proteins:1.Saturation effect;2.High specificity;3.Tightly regulated Transport and transport systemsAdenosine TriPhosphate(ATP)Structure of membrane-spanning transporters and types of transport eventsTransport and transport systems Function of the lac permease symporter of Escherichia coli and several other well-characterized simple transportersSimple transport Mechanism of the phosphotransferase system of Escherichia coliPhosphoenolpyruvate(PEP)PyruvateGroup translocation Mechanism of an ABC transporterABC systemABC:ATP-binding cassetteGram-negative bacteria ATP systemCell WallCell wall protects the cell from bursting resulting from high osmolar pressure conferred by high concentration of amino acid,salt and nucleic acids.It also shapes the cell and keeps the cell rigid.Cell Wall and MembraneGram-positiveGram-negativeGram was a modest man,and in his initial publication he remarked,I have therefore published the method,although I am aware that as yet it is very defective and imperfect;but it is hoped that also in the hands of other investigators it will turn out to be useful.Gram stainingCell Wall and MembraneRepeating unit in peptidoglycanCross-linked peptidoglycanor lysineOver 100 peptidoglycans found,Diversity of Peptidoglycan:M and G are constant in all kind of peptidoglycanTetrapeptide show major variation.M and DAP are bacteria specificThere are D-amino acidsPolysaccharidebackbonePeptidesEscherichia coli(gram-negative)Staphylococcus aureus(gram-positive)InterbridgePeptide bondsGlycosidic bondsXYCell Wall and MembraneCatalyzed by DD-transpeptidaseTarget of PenicillinCell Wall and MembraneGram-positive bacteria cell wall:1.90%of the cell wall is peptidoglycan2.Several glycan strands form a peptidoglycan“cable”(50nm wide)that become cross-linked to form an even stronger cell wall structure.3.Many G+bacteria have teichoic acids(磷壁酸）磷壁酸）in inserted in peptidoglycan,in which polyalcohol are usually connected by phosphate.It also contains sugars and alanine.4.Some teichoic acids bind to membrane lipid.Cell Wall and MembraneGram negative bacteria1.Only 10%of cell wall is peptidoglycan;2.Outer cell membrane，second phospholipid bilayerMost of the outer layer is replaced by LPS,inner layer by lipoprotein.Thus this bilayer is distinct from the real cytoplasmic membrane.3.Periplasm，filled with gel-like in consistency because of high concentration of proteins including hydrolytic enzymes,binding proteins for transport chemoreceptors Outer Membrane of Gram NegativeLPS:1.Chemical structure,3 main componentsLipid A:not a glycerol lipid,fatty acids are connected through amine group with modified disaccharides.KDO:ketodeoxyoctonate.the disaccharide is connected KDO that is attached to core polysaccharide chain.Polysaccharides chain contains two parts.1.core polysaccharide 2.O-specific polysaccharidePorin:transmembrane proteins with 3 identical subunits.Four holes.Nonspecific porinwater-filled channels.Specific porin one or a group of structurally related substancesPorins make outer membrane permeable Cell wall of Gram NegativeOuter membrane functions:1)structural;protect the periplasm protein from diffusing awaytransport molecules 2)toxic to animals in pathogenic bacteria,and the toxicity is associated with lipid A(endotoxin)3)Periplasm function.filled with gel-like in consistency because of high concentration of proteins including hydrolytic enzymes,binding proteins for transport，chemoreceptorsABC TransportI.Preparing a smearII.Heat fixing and stainingIII.MicroscopySpread culture in thinfilm over slidePass slide throughflame to heat fixDry in airFlood slide with stain;rinse and dryPlace drop of oil on slide;examine with 100 objective lensSlideOilStep 1Result:All cells purpleResult:All cells remain purpleResult:Gram-positivecells are purple;gram-negativecells are colorlessResult:Gram-positive(G+)cells are purple;gram-negative(G-)cellsare pink to redFlood the heat-fixedsmear with crystalviolet for 1 minAdd iodine solutionfor 1 minDecolorize withalcohol briefly about 20 secCounterstain withsafranin for 12 minG+G-Step 2Step 3Step 4Cell Wall and Membrane-Cells that lack cell wallsMycoplasmas:Free-living protoplasts1.Habitat 2.Tough cytoplasmic membrane(sterols)Cell Surface StructuresCover structures:Capsules;Slime Layers1)on cell surface,may be thick or thin,rigid or flexible2)polysaccharides or protein3)not considered as part of the cell wall because they do not confer significant structural strength,which is different from cell wall and cell membrane.CapsuleSlime layerCapsule usually consists of polysaccharides,but can be composed of other materials(e.g.,polypeptide in B.anthracis.A tight and well ordered matrix that excludes small particles including antibiotics.Function1)Capsule binds a significant amount of water,so it could play some role in resistance of the cell to desiccation.2)Can survive chemical sterilization,leaving autoclaving and flushing with boiling water as the only certain methods of decontamination 3)Capsules also help cells adhere to surfaces.Some pathogenic bacteria use capsule to adhere to host surface.4)The capsule is considered a virulence factor(pathogenicity factor)because it enhances the ability of bacteria to cause disease(e.g.prevents phagocytosis by not being recognized by phagocytic cells of immune system).There are 14 different capsule types(serotypes),which each impart their own specific antigenicity.Immunity to one capsule type does not result in immunity to the other types.Rhizobium trifolii stained with ruthenium redRhodobacter capsulatusAcinetobacter stained with India inkSlime layer consists mostly of polysaccharides,glycoproteins,and glycolipids.Loosely attached,easily removed,unorganized and can be lost from the cell surface.Function:Resistance to antibiotics,desiccation attachmentA biofilm is any group of microorganisms in which cells stick to each other on a surface.Polysaccharides layers play a key role in the development of biofilm.Biofilm formed solid surfacesFlagellaFimbriaeCell Surface StructuresFilamentous structures:Fimbriae(菌毛),Pili(性菌毛/纤毛),Flagellium(鞭毛)Cell Surface StructuresFilamentous protein structuresEnable organisms to stick to surfaces(many cells form pellicles on liquid surface,biofilm on solid surface)Fimbriae(菌毛)Cell Surface Structures/PiliTypically longer than fimbriae,but only one or a few pili are present on the surface of a cell.Many kinds of pili are known and distinguished by their structures and function 1)Assist in surface attachment 2)Facilitate genetic exchange between cells(conjugation)3)Type IV pili involved in twitching motility/adhension/transformation The pilus on an E.coli cell that is undergoing conjugationType IV Pili&Twitching DonorRecipientCell Inclusions storing nutrientsCarbon storage polymersPoly-hydroxybutyric acid(PHB):lipid(Figure 3.26)Glycogen:glucose polymerPolyphosphates:accumulations of inorganic phosphate(Figure 3.27)Sulfur globules:composed of elemental sulfur Food storage is a strategy for getting through hard times when resources are low because of seasonal or other factors.Cell inclusion for storing carbon GlycogenPHAPolyphosphateSulfurPhosphate is a major component is cell membrane and nucleic acid and ATP.Phosphate is often a limiting nutrient in nature environment because it exists as rock phosphate that is not consumable for bioorganisms.Reduced sulfur such as H2S can be oxidized to sulfate,generating reductant for chemolithotrophy or CO2 fixation(autotrophy).Stored in the periplasm.Heliobacterium modesticaldumSulfur globulesa-sulfurLong chain sulfurCell inclusion -Function unknown Megnetosomes(磁小体）磁小体）:1.Particles of iron mineral magnetite(Fe3O4)surrounded by a thin membrane.2.Confer magnetotaxis and bacterial cells can response to a magnetic field,.3.Function unknown,could guide the cells to a specific ecological niches because of Earths magnetic field.Gas Vesicles(mainly in aquatic microorganisms)Gas VesiclesConfer buoyancy in planktonic cells by decreasing cell density,allowing microorganisms to stay optimal region,such as light intensity.Only found in bacteria and archaea,never found in eukaryotic microorganisms.Spindle-shaped,gas-filled structures made of proteinGas vesicle impermeable to water but gas-permeable.The composition of pressure of gas is that of the gas from the environment.CyanobacteriaA fresh water lake Wisconsin,USARibsGvpAGvpCMolecular Structure of Gas VesiclesEndosporesHighly differentiated cells and survival structure resistant to heat,harsh chemicals,and radiation Ideal for dispersal via wind,water,or animal gutOnly present in some gram-positive bacteria“Dormant”stage of bacterial life cycle Vegetative cell endospore vegetative cell Frogs hibernateDormant bacteriaFigure 3.33Vegetative cellDeveloping sporeSporulating cellMature spore 2012 Pearson Education,Inc.Endospore structureExosporium:a thin protein covering(Function:unknown,but could exclude toxic chemicals)Spore coat:layers of spore-specific proteins.(Function:resistance to many toxic molecules by exclusion)Cortex:loosely cross-linked peptidoglycan(Function:life essential components)Core:cytoplasmic membrane,cytoplasma,nucleoid,and other essentials.(Function:life essential components)The endospore differs structurally from the vegetative cell primarily in the kinds of structures found outside the core wall.COREEndosporeEndospore coreEndospore-specific substance is dipicolinic acid that is complexed with Ca2+,and calcium dipicolinate represents 10%of endospore dry weight.Calcium dipicolinate binds free water and reduces the water content of the core,and the core of mature endospore has only 10-25%of the water content of the vegetative cells.Dehydration of the core greatly increases the heat resistance of marcomolecules within the spore,survive 150C.121C is usually for microbiological sterilization.Dehydration confers resistance to chemicals.The complex intercalates in DNA for stabilization.Small acid-soluble proteins(SASPs)1.Bind tightly to DNA and change DNA structure from B form to A form to protect it from UV,desiccation and heat;2.Function as carbon and energy sourceFree endosporeStage VI,VIIStage VCoatStage IVStage IIIStage IIMother cellPresporeSeptumSporulation stagesCortexCell wallCytoplasmicmembraneVegetative cycleMaturation,cell lysisCelldivisionGerminationGrowthEngulfment Asymmetriccell division;commitmentto sporulation,Stage ISpore coat,Ca2 uptake,SASPs,dipicolinic acidCortexformation 2012 Pearson Education,Inc.The Sporulation Process Sporulation and EndosporesEndospore germination in Bacillusa.Endospore b.Refractility is being lostc.&d.The new vegetative cell is emerging.V.Microbial Locomotion3.13 Flagella and Motility3.14 Gliding Motility3.15 Microbial Taxeshttp:/ swimming motility powered by the rotation of flagellar filaments.(b)Sheathed flagelladriven motility by spirochetes suitable in highly viscous fluids.(c)Swarming motility on a solid surface powered by multiple lateral flagellar filaments.(d)Social gliding motility resulting from the retraction of type IV pili adhered to a solid surface or other bacterial cell bodies.(e)Mechanism for adventurous gliding motility proposed by Mignot et al.5.Flagella Swimming in liquidDifferent arrangements:Helical in shapelophotrichousPolarPeritrichousHelicalConstant distance(wavelength)between adjacent curve,characteristic for any given species.Flagellin is a protein consisting of a conserved inner core,accountable for the self-assembly of monomeric units,and an outer surface portion.D0,D1,D2 and D3 form the most inner portion and D3 the most outer surface portion.Flagellin11 flagellins formed into one helical unit.MS ringother anchor ringshookprotein cap-filamentFilament grow from its tip,flagellin molecules synthesized in cytoplasm travel through the channel to the tip.Broken filament can be repaired.RotorBasal bodyStatorGenerate torqueTorque=力力x力臂力臂Flagellium moves like propellerProton turbine modelProton motive force drives rotation of flagellumFlagella increase or decrease rotational speed in relation to strength of the proton motive force.Peritrichously flagellated cells move slowly and deliberately.Cell speed and motionPolarly flagellated cells move more rapidly and typically spin aroundReversible flagellaUndirectional flagellaGliding Motility on solid surfaceGliding MotilityFilamentous or rod-shaped cellsSlower and smoother than swimmingMovement typically occurs along long axis of cellRequires surface contactFlavobacteriumE.coliExcretion of polysaccharide slimeGliding mechanismsGliding-specific proteinsType IV Pili&Twitching 3.15 Microbial TaxesTaxis:directed movement in response to chemical or physical gradientsChemotaxis:response to chemicalsPhototaxis:response to lightAerotaxis:response to oxygenOsmotaxis:response to ionic strengthHydrotaxis:response to waterChemotaxisBest studied in E.coliBacteria respond to temporal,not spatial,difference in chemical concentration“Run and tumble”behavior(Figure 3.47)Attractants and receptors sensed by chemoreceptorsMeasure chemotaxis using a capillary tube assayPhototaxis/scotophobotaxisPhototaxis phototrophic bacteriaDifferent phototrophic bacteria like different lightScotophobotaxis
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