原核微生物形态构造及功能.ppt

**细菌形态指细胞形态**◆BacterialshapeTheFigurebelowshowsfourofthecommonandcharacteristicshapesofbacteria:cocci(spherical),rods,vibrio(commashaped)andspiral.Cocci.Theorganismshown(topleft)isMicrococcusluteus,whichformstetradsduetoregularalternationoftheplaneofcelldivision.Micrococcusspeciesarecommonlyassociatedwiththeskin.Staphylococcusspeciesalsoarecommonontheskin,andS.aureuscausesboilsor,occasionally,moreseriousinfections.Streptococcusspeciesalsoarecommonbuttypicallyformchainsofcellsbecausetheydivideinasingleplane.Streptococcusmutanscommonlygrowsontoothenamelandcontributestotoothdecay(dentalcaries).Rods.Theorganismshown(topright)isBacilluscereus,acommoninhabitantofsoilbutalsofoundonmanyfoodproducts.AllBacillusspeciesproduceendospores,seeninvariousstagesofdevelopmentinthephotograph;eventuallytheyarereleasedwhenthecellslyse.B.cereuscausesarelativelymildfoodpoisoning,especiallyonreheatedfriedriceintake-awayfoodoutlets.Thesporescanresistdestructionduringcookingandcanthengerminateifthecookedfoodisnotrefrigerated.Twotoxinsareformed:oneisheat-stable,isproducedduringsporulationandcausingvomiting;theotherisheat-labile,isproducedduringexponentialgrowthandcausesdiarrhoea.

Vibrio.Theorganismshown(bottomleft)isVibrioalginolyticus,anagar-degradingspeciesfoundinmarineenvironments.Theorganismsinthephotographareclusteredtogetherinanextracellularpolysaccharide(slime)thattheysynthesized,andmanyofthemaredividingsotheyareseeninpairs.Thebest-knownspeciesofVibrioisV.choleraewhichcausescholera,aseverediarrhoealdiseaseresultingfromatoxinproducedbybacterialgrowthinthegut.Spiral.Theorganismshown(bottomright)isaspeciesofRhodospirillum,oneofthepurplenon-sulphurbacteria(seeWinogradskycolumn).Typically,t