Viruses, Bacteria & Archaea

Chapter 21

2Viruses, BacterViruses, Bacteria & Archaeaia & ArchaeaOutlineOutline

VirusesViruses StructureStructure ClassificationClassification ReproductionReproduction

ProkaryotesProkaryotes StructureStructure ReproductionReproduction NutritionNutrition

BacteriaBacteriaArchaeaArchaea

3Viruses, BacterViruses, Bacteria & Archaeaia & ArchaeaThe VirusesThe Viruses

Viruses are noncellular and thus cannot be Viruses are noncellular and thus cannot be classified with cellular organismsclassified with cellular organisms

Generally smaller than 200 nm in diameterGenerally smaller than 200 nm in diameterEach type has at least two partsEach type has at least two parts

Capsid: Outer layer composed of protein Capsid: Outer layer composed of protein subunitssubunits­Some enveloped by membraneSome enveloped by membrane­Others “naked”Others “naked”

Nucleic acid core: DNA or RNANucleic acid core: DNA or RNAVary in shape from thread-like to Vary in shape from thread-like to polyhedralpolyhedral

4Viruses

5Viruses, BacterViruses, Bacteria & Archaeaia & ArchaeaViral CategorizationViral Categorization

Classification is based on:Classification is based on:Type of nucleic acidType of nucleic acidSize and shapeSize and shapePresence / absence of outer envelopePresence / absence of outer envelope

6Viruses, BacterViruses, Bacteria & Archaeaia & ArchaeaParasitic NatureParasitic Nature

Viruses are:Viruses are:Obligate intracellular parasitesObligate intracellular parasitesCannot reproduce outside a living cellCannot reproduce outside a living cellCan be cultured only inside living cellsCan be cultured only inside living cells­Chicken egg Chicken egg ­ Tissue cultureTissue culture

7“Growing” Viruses

8Viruses, BacterViruses, Bacteria & Archaeaia & ArchaeaThe Bacteriophages:The Bacteriophages:ReproductionReproduction

Bacteriophages – Viruses that infect Bacteriophages – Viruses that infect bacterial cellsbacterial cells

Portions of capsid adhere to specific Portions of capsid adhere to specific receptor on the host cellreceptor on the host cell

Viral nucleic acid enters the cellViral nucleic acid enters the cellOnce inside, the virus takes over Once inside, the virus takes over metabolic machinery of the host cellmetabolic machinery of the host cell

9Viruses, BacterViruses, Bacteria & Archaeaia & ArchaeaBacteriophages:Bacteriophages:The Lytic CycleThe Lytic Cycle

Lytic cycle may be divided into five Lytic cycle may be divided into five stages:stages:AttachmentAttachmentPenetrationPenetrationBiosynthesisBiosynthesisMaturationMaturationReleaseRelease

10Viruses, BacterViruses, Bacteria & Archaeaia & ArchaeaThe Bacteriophages:The Bacteriophages:The Lysogenic CycleThe Lysogenic Cycle

Phage becomes a prophagePhage becomes a prophageBecomes integrated into the host Becomes integrated into the host genomegenome

Becomes latentBecomes latentMay later reenter the lytic cycleMay later reenter the lytic cycle

11Lytic and Lysogenic Cycles in Prokaryotes

12Viruses, BacterViruses, Bacteria & Archaeaia & ArchaeaReproduction of Animal VirusesReproduction of Animal Viruses

Animal virus enters the host cellAnimal virus enters the host cellUncoating releases viral DNA or RNAUncoating releases viral DNA or RNA

Budding:Budding:­Viral particles released in a budViral particles released in a bud­Acquires a membranous envelopeAcquires a membranous envelope

Retroviruses (AIDS)Retroviruses (AIDS)­Contain reverse transcriptaseContain reverse transcriptase­Carries out RNA Carries out RNA cDNA reverse cDNA reverse transcriptiontranscription­ cDNA becomes integrated into host DNAcDNA becomes integrated into host DNA

13Reproduction of the Retrovirus HIV-1

14Viruses, BacterViruses, Bacteria & Archaeaia & ArchaeaViral InfectionsViral Infections

Viruses are best known for causing infectious Viruses are best known for causing infectious diseases in plants and animalsdiseases in plants and animals Herpes, HIV, cancerHerpes, HIV, cancer­ Viruses lack metabolism; thus, antibiotics have Viruses lack metabolism; thus, antibiotics have no effectno effect

ViroidsViroids­ Naked strands of RNANaked strands of RNA­ Many crop diseasesMany crop diseases

PrionsPrions­ Protein molecules with contagious tertiary Protein molecules with contagious tertiary structurestructure

­ Some human and other animal diseases - Mad Some human and other animal diseases - Mad cow diseasecow disease

15Viruses, BacterViruses, Bacteria & Archaeaia & ArchaeaThe ProkaryotesThe Prokaryotes

Include bacteria and archaea, which Include bacteria and archaea, which are fully functioning cellsare fully functioning cellsA single spoonful of earth can contain A single spoonful of earth can contain >1000 prokaryotes>1000 prokaryotes

Range in size from 1-10 Range in size from 1-10 µµm in length m in length and 0.7-1.5 and 0.7-1.5 µµm in widthm in width

16Pasteur’s Experiment

17Viruses, BacterViruses, Bacteria & Archaeaia & ArchaeaProkaryote StructureProkaryote Structure

Lack a membrane-bounded nucleus Lack a membrane-bounded nucleus (DNA in nucleoid region)(DNA in nucleoid region)

Outer cell wall containing Outer cell wall containing peptidoglycanpeptidoglycan

Some move by means of flagellaSome move by means of flagellaLack membranous organellesLack membranous organellesMay have accessory ring of DNA May have accessory ring of DNA (plasmid)(plasmid)

18Flagella

19Viruses, BacterViruses, Bacteria & Archaeaia & ArchaeaReproduction in ProkaryotesReproduction in Prokaryotes

AsexualAsexualProkaryotes reproduce asexually by Prokaryotes reproduce asexually by means of binary fissionmeans of binary fission

Methods of genetic recombinationMethods of genetic recombinationConjugationConjugation­Sex pilus forms between two cellsSex pilus forms between two cells­Donor cell passes DNA to recipient cell Donor cell passes DNA to recipient cell through pilusthrough pilus

TransformationTransformationTransductionTransduction

20Fimbriae and Sex Pilus

21Binary Fission

22Viruses, BacterViruses, Bacteria & Archaeaia & ArchaeaReproduction in ProkaryotesReproduction in Prokaryotes

TransformationTransformationOccurs when bacterium picks up free Occurs when bacterium picks up free pieces of DNA from other prokaryotespieces of DNA from other prokaryotes

Becomes incorporated into genomeBecomes incorporated into genomeTransductionTransduction

Occurs when bacteriophages carry Occurs when bacteriophages carry portions of bacterial DNA from one cell to portions of bacterial DNA from one cell to anotheranother

Serve as vectorsServe as vectorsSome bacteria form resistant endospores Some bacteria form resistant endospores under unfavorable conditionsunder unfavorable conditions

23The Endospore of Clostridium tetani

24Viruses, BacterViruses, Bacteria & Archaeaia & ArchaeaProkaryotic NutritionProkaryotic Nutrition

Oxygen requirements:Oxygen requirements:Obligate aerobes – unable to grow in Obligate aerobes – unable to grow in the absence of free oxygenthe absence of free oxygen

Obligate anaerobes – unable to grow Obligate anaerobes – unable to grow in the presence of free oxygenin the presence of free oxygen

Facultative anaerobes – able to grow Facultative anaerobes – able to grow in either the presence or absence of in either the presence or absence of free oxygenfree oxygen

25Viruses, BacterViruses, Bacteria & Archaeaia & ArchaeaAutotrophic ProkaryotesAutotrophic Prokaryotes

PhotoautotrophsPhotoautotrophsUse solar energy to reduce carbon Use solar energy to reduce carbon dioxide to organic compoundsdioxide to organic compounds

PhotosyntheticPhotosyntheticChemoautotrophsChemoautotrophs

Oxidize inorganic compounds to obtain Oxidize inorganic compounds to obtain the necessary energythe necessary energy

Use it to reduce COUse it to reduce CO22 to an organic to an organic compoundcompound

ChemosyntheticChemosynthetic

26Viruses, BacterViruses, Bacteria & Archaeaia & ArchaeaHeterotrophic ProkaryotesHeterotrophic Prokaryotes

Most prokaryotes are chemoheterotrophs Most prokaryotes are chemoheterotrophs that take in organic nutrientsthat take in organic nutrientsAerobic saprotrophs decompose most Aerobic saprotrophs decompose most large organic molecules to smaller large organic molecules to smaller moleculesmolecules

Essential components of healthy Essential components of healthy ecosystemecosystem

May be free-living or symbioticMay be free-living or symbioticNitrogen fixationNitrogen fixationCommensalismCommensalismParasitesParasites

27Nodules of a Legume

28Viruses, BacterViruses, Bacteria & Archaeaia & ArchaeaThe BacteriaThe Bacteria

Bacteria are commonly diagnosed Bacteria are commonly diagnosed using the Gram stain procedureusing the Gram stain procedure

When washed after staining:When washed after staining:Gram-positive bacteria retain dye and Gram-positive bacteria retain dye and appear purpleappear purple

Gram-negative bacteria do not retain Gram-negative bacteria do not retain dye and appear pinkdye and appear pink

29Viruses, BacterViruses, Bacteria & Archaeaia & ArchaeaThe BacteriaThe Bacteria

Structure of cell wall also of Structure of cell wall also of diagnostic usediagnostic use

Bacteria can be further classified in Bacteria can be further classified in terms of their three basic shapesterms of their three basic shapesSpiral (spirilli),Spiral (spirilli),Rod (bacilli), andRod (bacilli), andRound (cocci)Round (cocci)

30Diversity of Bacteria

31Viruses, BacterViruses, Bacteria & Archaeaia & ArchaeaCyanobacteriaCyanobacteria

Formerly called the Blue-Green algae Formerly called the Blue-Green algae (Cyanophyta)(Cyanophyta)

Cyanobacteria are Gram-negative Cyanobacteria are Gram-negative bacteria that photosynthesizebacteria that photosynthesize

Believed to be responsible for Believed to be responsible for introducing oxygen into the primitive introducing oxygen into the primitive atmosphereatmosphereLack visible means of locomotionLack visible means of locomotionCan live in extreme environmentsCan live in extreme environmentsWhen commensals with fungi, form When commensals with fungi, form lichenslichens

32Diversity Among the Cyanobacteria

33Viruses, BacterViruses, Bacteria & Archaeaia & ArchaeaThe ArchaeaThe Archaea

Archaea were earlier considered Archaea were earlier considered bacteriabacteria

Carl Woese discovered that the base Carl Woese discovered that the base sequence of their rRNA differs from sequence of their rRNA differs from BacteriaBacteria

Other differences:Other differences:Archaea do not have peptidoglycan in Archaea do not have peptidoglycan in their cell walls like the Bacteriatheir cell walls like the Bacteria

Archaea biochemical more like Eukarya Archaea biochemical more like Eukarya than Bacteriathan Bacteria

Archaea now thought to be more closely Archaea now thought to be more closely related to Eukarya than to Bacteriarelated to Eukarya than to Bacteria

34Viruses, BacterViruses, Bacteria & Archaeaia & ArchaeaArchaea MetabolismArchaea Metabolism

Most are chemoautotrophsMost are chemoautotrophsSome mutualisticSome mutualisticSome commensalisticSome commensalisticNone known to be parasiticNone known to be parasiticNone are photosyntheticNone are photosyntheticMany live in harsh conditionsMany live in harsh conditions

35Viruses, BacterViruses, Bacteria & Archaeaia & ArchaeaTypes of ArchaeaTypes of Archaea

Many live in harsh conditions:Many live in harsh conditions: Anaerobic marshesAnaerobic marshes­ MethanogensMethanogens­ Produce methane from hydrogen gas and Produce methane from hydrogen gas and carbon dioxidecarbon dioxide

Salty lakesSalty lakes­ HalophilesHalophiles­ Require high salt concentrations for growth, Require high salt concentrations for growth, andand

Hot sulfur springsHot sulfur springs­ ThermoacidophilesThermoacidophiles­ Reduce sulfides and survive best at Reduce sulfides and survive best at temperatures above 80ºCtemperatures above 80ºC

­ Plasma membranes contain unusual lipids Plasma membranes contain unusual lipids convey tolerance of high temperaturesconvey tolerance of high temperatures

36Thermoacidophile Habitat and Structure

37Viruses, BacterViruses, Bacteria & Archaeaia & ArchaeaReviewReview

VirusesViruses StructureStructure ClassificationClassification ReproductionReproduction

ProkaryotesProkaryotes StructureStructure ReproductionReproduction NutritionNutrition

BacteriaBacteriaArchaeaArchaea

Viruses, Bacteria & Archaea

Ending Slide Chapter 21