Your SlideShare is downloading. ×
Bacteria & Viruses
Upcoming SlideShare
Loading in...5

Thanks for flagging this SlideShare!

Oops! An error has occurred.

Saving this for later? Get the SlideShare app to save on your phone or tablet. Read anywhere, anytime – even offline.
Text the download link to your phone
Standard text messaging rates apply

Bacteria & Viruses


Published on

  • thats good effort
    Are you sure you want to  Yes  No
    Your message goes here
  • good..

    Please assist me in mailing the bacteria & virus presentation to my ID please.
    Are you sure you want to  Yes  No
    Your message goes here
  • great
    Are you sure you want to  Yes  No
    Your message goes here
No Downloads
Total Views
On Slideshare
From Embeds
Number of Embeds
Embeds 0
No embeds

Report content
Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

No notes for slide


  • 1. Bacteria & Viruses Prokaryotes and Beyond
  • 2. The Prokaryotes
    • Prokaryotes = Monerans
    • The earliest organisms
      • lived & evolved alone on earth for 2 x 10 9 years
    • The smallest independently living things
      • Much smaller than single celled eukaryotes
      • Typical bacteria = 2 µ
      • Average eukaryotic cell = 50-200 µ
    • Outnumber all eukaryotes combined
      • more inhabit your mouth than the total # of people who ever lived!
  • 3. Diversity & Classification
    • 2 branches
    • Archebacteria
      • Confined to extreme environments
      • Similar to early earth
      • More closely related to eukaryotes than to modern bacteria
    • Only a few genera:
      • Methanogens - reduce CO 2 to CH 4
      • Extreme halophiles - salt loving
      • Thermoacidophiles
    • Eubacteria
      • most modern bacteria
      • very diverse
  • 4. Bacterial Classification
  • 5. Prokaryotes vs. Eukaryotes
    • No mitochondria, chloroplasts, or other membrane bound organelles
    • Most are unicellular and much smaller
    • Smaller, simpler genomes
      • DNA not arranged in chromosomes
    • Cell wall is different from plants, fungi, protists
      • contains murein / peptidoglcan (a nitrogen containing polysaccharide)
    • Differ in mechanisms of genetic replication, expression, and recombination
  • 6. Prokaryotic & Eukaryotic Cells
  • 7. Function & Interactions
    • Only a minority cause disease
    • Many are essential to life on earth
    • Decomposers
      • essential to chemical cycles
    • Often live in symbiotic relationships with other organisms
  • 8. Form & Function
    • Single celled
      • some aggregate in 2-celled or several celled groups
      • some form colonies
    • Diversity of shapes
    • 3 most common:
      • spheres = cocci
      • rods = bacilli
      • spirals = spirilla
  • 9. Bacterial Shapes
  • 10. The Bacterial Cell Wall
    • Instead of cellulose, contain peptidoglycan
      • A polymer of modified sugars cross-linked with amino acids
    • The gram stain distinguishes many disease causing bacteria based on the type of cell wall
    • Many antibiotics work by attacking the bacterial cell wall
  • 11. The Gram Stain
    • A valuable tool for distinguishing types of bacteria based on the cell wall
    • Gram (+)
      • accept gram stain
      • have simpler cell walls with large amounts of peptidoglycan
    • Gram (-)
      • do not stain
      • have more complex cell walls with less peptidoglycan
      • cell walls contain lipopolysaccharides
      • are more likely to be pathogenic (cause disease)
      • more resistant to antibiotics
  • 12. The Cell Wall & Gram Stain
  • 13. Gram (+) and (-) Bacteria
  • 14. Antibiotics
    • Many antibiotics work on the cell wall
    • Common antibiotics (e.g. penicillin) work by preventing cross-linking of peptidoglycan
    • Therefore bacteria can’t form new cell walls
    • Therefore no new bacteria are formed
    • Doesn’t effect the host, because only monerans have peptidoglycan
    • Explains added resistance of gram (-) bacteria to these antibiotics
  • 15. Secretion of Antibiotics
    • Most micro-organisms (including protists, monerans & fungi) release antibiotics
    • An evolutionary advantage
    • Helps the organism compete for food and space
  • 16. The Capsule
    • Many bacteria secrete a sticky substance that forms another protective layer, the capsule
    • Outside the cell wall
    • Helps them stick to things
    • Provides protection
  • 17. Motility
    • About half of all monerans are capable of directional movement.
    • 3 mechanisms:
      • flagella - different from eukaryotes
      • spiral shaped bacteria ( spirochetes ) have a filament that spirals around the cell under the outer sheath
        • causes the cell to move like a corkscrew
      • some bacteria secrete slimy chemicals & glide
    • Taxis
      • movement toward or away from a stimulus
      • many bacteria exhibit this form of movement
  • 18. Structure of Prokaryotic Flagella
  • 19. Structures of Movement
  • 20. Prokaryotic Ribosomes
    • Slightly different from eukaryotic ribosomes
    • The basis of some antibiotics
      • tetracycline & chloramphenicol
      • block protein synthesis in prokaryotes only
  • 21. Metabolic Diversity
    • A varied group, similar to eukaryotes
    • Three major groups:
    • Phototrophs
      • use light energy to synthesize organic compounds from CO 2
      • includes cyanobacteria (blue-green algae)
      • have chlorophyll but not chloroplasts
    • Photoheterotrophs
      • can use light to generate ATP
      • must obtain carbon in organic form
    • Chemoheterotrophs
      • Must consume organic molecules for both energy & carbon
      • Most bacteria are chemoheterotrophs
  • 22. Chemoheterotrophs
    • Most bacteria are chemoheterotrophs
    • Consume organic molecules for both energy and carbon
    • Secrete an enzyme that breaks down large molecules of food to smaller molecules that can be absorbed through the cell membrane
    • Many bacteria are saprobes
      • feed on dead plants or animals
      • also called decomposers because they break down decaying material
    • Other bacteria live in or on the bodies of other living organisms
      • some are beneficial ( symbiosis )
      • some are harmful = parasites
  • 23. Oxygen
    • The effects of oxygen on growth are varied
    • Obligate aerobes
      • cannot grow without O 2 for cellular respiration
    • Facultative aerobes
      • use O 2 if available but can also use fermentation
    • Obligate anaerobes
      • cannot use O 2 and are poisoned by it. 
    • Facultative anaerobes
      • don't use O 2 , but aren't harmed
    • Many heterotrophic bacteria are anaerobes
      • classified by their metabolic wastes (acetic acid, lactic acid, etc.)
  • 24. Nitrogen Metabolism
    • Also diverse
    • Monerans are able to metabolize most nitrogen compounds
    • Key to cycling nitrogen through the ecosystem
    • Nitrogen fixation
      • Some monerans can capture N 2 in the atmosphere
      • They have an enzyme that converts N 2 gas to nitrates (NO 3 ) - a form other organisms can use
      • This is the only mechanism that makes atmospheric nitrogen available to other organisms
      • Some plants (clover, beans, etc.) have nitrogen fixing bacteria growing in their roots
  • 25. The Bacterial Genome
    • Bacteria have ~ 1/1000 as much DNA as eukaryotes
    • DNA is one double stranded molecule in the form of a ring
    • No nucleus, so DNA is in the cytoplasm
  • 26. Plasmids
    • Bacteria may also have smaller rings of DNA called plasmids
    • Each plasmid is only a few genes
    • Plasmids carry non-essential genes such as antibiotic resistance, metabolism of special nutrients, etc.
    • Plasmids can carry a sex factor
      • bacteria with the sex factor can conjugate with cells that do not carry the factor.
    • Plasmids replicate independently
    • Can be transferred when bacteria conjugate
  • 27. Growth & Reproduction
    • Neither mitosis nor meiosis occurs in prokaryotes
    • Prokaryotes reproduce asexually by binary fission
    • Genetic recombination does occur in bacteria
  • 28. Genetic Exchange
    • 3 mechanisms of exchange of genetic material:
    • transformation -
      • genes taken up by bacteria from the surrounding environment
    • conjugation -
      • genes are transferred directly from one bacteria to another
    • transduction -
      • genes are transferred between bacteria by means of viruses
    • All are unilateral passage of variable amounts of DNA
    • Mutation is the major source of genetic variation in prokaryotes
  • 29. Bacterial Conjugation
  • 30. Endospores
    • Some bacteria form resistant cells called endospores
    • Can live in stasis indefinitely
      • found 11,000 y.o. bacteria
    • Resist extremes of temperature, pH, etc.
  • 31. Classes of Bacteria
    • The Eubacteria include:
      • Proteobacteria
      • Chlamydia
      • Spirochetes
      • Gram-positive bacteria
      • Cyanobacteria
    • The Archebacteria include:
      • Euryarchaeota
      • Crenarchaeota
  • 32. Prokaryotic Phylogeny
  • 33.
    • There are 5 major clades (divisions) of eubacteria
  • 34. The Proteobacteria
    • A diverse group of gram-negative bacteria
    • Includes photoautotrophs, chemoautotrophs & heterotrophs
    • Includes both anaerobic & aerobic species
    • 5 subgroups:
      • Alpha proteobacteria
      • Beta proteobacteria
      • Gamma proteobacteria
      • Delta proteobacteria – myxobacteria
      • Epsilon proteobacteria - helicobacter
  • 35. Subgroups of Proteobacteria
    • Alpha proteobacteria
      • Most are symbionts or parasites
      • Includes rhizobium, nitrogen fixing bacteria found in the roots of legumes
    • Beta proteobacteria
      • Includes nitosomonas – oxidize NH 4 producing nitrite
    • Gamma proteobacteria
      • Includes photosynthetic bacteria and many enterics such as E. coli , Legionella , Vibrio cholera , salmonella
    • Delta proteobacteria
      • Includes Myxobacteria which form elaborate colonies
      • Bdellovibrios – predators that attack other bacteria
    • Epsilon proteobacteria
      • Closely related to deltas
      • Includes helicobacter which causes stomach ulcers
  • 36. Chlamydia
    • Parasites that can survive only within the cells of animals
    • Gram negative walls are unusual because they lack peptidoglycan
    • One species is the most common cause of blindness in the world
    • Another species causes the most common STD in the U.S.
  • 37. Spirochaetes
    • Helical heterotrophs
    • Have axial filaments = fibers between cell wall and cell membrane
      • Filaments allow a corkscrew motion
    • Many are free living
    • Includes anaerobes that live in mud or H 2 O
    • A few are parasites
    • Includes the organisms that cause syphilis and Lyme disease
  • 38. Gram Positive Bacteria
    • Includes all gram positive bacteria and also a few related gram negative bacteria
    • Colonial actinomycetes were once mistaken for fungus
      • includes Streptomyces , the source of many antibiotics
      • Also includes species that cause tuberculosis & leprosy
    • Includes spore formers such as such as Bacillus & Clostridium
      • Bacillus anthracis
      • Clostridium botulinum
      • Also all Staphylococcus & Streptococcus
    • Mycoplasmas
      • The only bacteria lacking a cell wall
      • Smallest known cells
      • Most live in soil
  • 39. Cyanobacteria
    • Only about 1,500 species
    • Sometimes called blue-green algae
    • Are photosynthetic
      • Don't contain chlorophyll
      • Have 2 photosynthetic pigments not found in plants:
      • phycocyanin - a blue-green pigment
      • phycoerythrin - a red pigment
    • Many are multicellular - form long filaments
      • To reproduce, chains of cells break, and cells at ends of chains divide, increasing length of the filament
    • Some contain heterocysts - thick walled cells that contain enzymes for nitrogen fixation
      • supply other cells with nitrogen
      • other cells supply them with food from photosynthesis
  • 40. Viruses
    • Much smaller than bacteria: .03 - .30
    • Can't be seen with a light microscope
    • Consist of a single molecule of nucleic acid surrounded by a protein coat
    • The nucleic acid molecule can be single or double stranded DNA, or RNA
    • The amount of nucleic acid is much less than bacteria
      • bacteria have enough DNA for 2000 genes
      • many viruses have only 10 genes; the largest is about 100 genes
  • 41. Viral Strategy
    • Viral genes carry instructions for the production of new virus particles
    • Viruses have no ribosomes or other cytoplasmic structures to carry out their genetic instructions
    • Viruses can't live independently; are all parasites of living cells
    • They use the energy and the protein producing machinery of the host cells to make new virus particles
  • 42. Viral Protection
    • The protein coat is made of several hundred protein molecules packed in a geometric pattern
    • Some have a complex capsule surrounding the protein coat
  • 43. Viral Structure
  • 44. Specificity
    • Each type of virus infects a particular type of cell
    • Viruses that infect bacteria = bacteriophage
      • have a ‘tail’ that attaches to bacteria
  • 45. A Bacteriophage
  • 46. Elements of a Bacteriophage
  • 47. Reproduction of Viruses
    • Two primary life cycles
      • Lytic cycle
      • Lysogenic cycle
    • Some have one life cycle or the other
    • Some can shift life cycle type depending on environmental pressures
  • 48. The Lytic Cycle
    • Example E.coli phage:
    • The tail fibers match molecules in host cell membrane - so bind specifically
    • Once the phage is attached, it acts like a syringe - injects its DNA into the host
    • Inside the cell, the phage DNA takes over the cytoplasmic machinery of the host cell
    • The host cell makes copies of the phage DNA
  • 49. The Lytic Cycle (Continued)
    • Host cell ribosomes make proteins according to phage gene instructions.
    • New phage proteins and nucleic acids come together in the cell and form several hundred new phage particles
    • The phage DNA instructs the host cell to self-destruct
    • The host cell makes an enzyme that lyses or digests the bacterial cell wall
    • When the host cell lyses, it releases new phage particles
  • 50. Lytic Cycle of the T4 Phage
  • 51. Modified Lytic Cycle
    • Some viruses have a modified lytic cycle
    • They don't lyse the host cell
    • The virus exits by pushing out through the cell membrane
    • These viruses have capsules that consist partly of host cell membrane & partly viral protein
    • Example: human influenza virus
  • 52. Viral Latency
    • Some viruses can take both active and latent forms.
    • During the active phase, the virus interferes with normal cell metabolism, causing disease symptoms
    • During the latent phase, it's as if the virus has gone to sleep.
      • Although the host cells remain infected, the host is a symptom-free carrier of the disease.
    • The difference between the active and latent manifestations of viral infection results from a switch in viral replication patterns.
      • Some viruses can only replicate by the lytic pathway.
      • Other viruses can inject their DNA into the host cell, but the injected DNA can be inactive until the appropriate cellular event triggers its awakening.
  • 53. The Lysogenic Cycle
    • The latter pathway is called the temperate or lysogenic pathway.
    • After entering the host cell, the viral DNA inserts into host DNA by recombination
      • viral DNA becomes part of host DNA
    • Viral DNA does not take over the host cell
    • When the host cell reproduces, viral genes are also duplicated
    • There may be no active viral particles produced for generations
    • Sporadically, viral DNA will become active and trigger reproduction
  • 54. The Lysogenic Cycle (Continued)
    • When lysogenic viral DNA becomes active, it breaks out of the host DNA  lytic
    • As it breaks out, the viral DNA may take several bacterial genes with it
    • The virus can carry bacterial genes from the previous host to a new host during the infection cycle
      • this process = transduction
      • used in recombinant DNA research
    • It is possible to artificially induce all the cells in a lysogenic culture to enter the lytic pathway by exposing them to UV light, or X-rays.
    • Example: Herpes virus (causes cold sores; may cause cancers
  • 55. Discovery of the Lysogenic Cycle
    • The lysogenic pathway was first discovered in bacteriophages in the early 1920s
    • It was not really understood until the 1950s
    • First explored at the cellular level by Andre' Lwoff, a French scientist.
    • Lwoff knew that some bacterial cultures that grew normally and otherwise seemed perfectly healthy were infected by phage.
    • Although the phage didn't interfere with the host bacteria, such cultures had the ability to cause the lysis or rupture of other bacteria.
    • Thus, the culture was described as "lysogenic."
  • 56. Unraveling the Lysogenic Cycle
    • It was known why such cultures were lethal to other bacteria.
    • The lysogenic effect didn't stem from phage particles floating in the culture
      • The cultures remained lethal even after removal of any free floating phage.
    • The effect was not due to a reserve of phage stored within the host cells
      • No phage were released when the cells of a lysogenic culture were artificially burst open.
  • 57. Lwoff’s Discovery
    • Lwoff observed the growth of single bacterial cells of Bacillus megaterium in tiny droplets of medium.
      • Found that free phage particles were never found floating in droplets that contained only single cells
      • They were found in the colonies derived from single cells.
      • Occasionally, a single cell in a droplet being watched would spontaneously burst, releasing about 100 phage.
    • Concluded that host cells weren’t entirely immune to the phage.
      • When a phage became active, it forced the host to make more phage, eventually killing the host, and releasing new phage when the cell burst.
      • But, the switch from the lysogenic to the lytic pathway was the exception rather than the rule; most of the time the phage was in an inactive form.
  • 58. Phage Lytic & Lysogenic Cycles
  • 59. Are Viruses Alive?
    • Viruses contain nucleic acids & proteins
    • Viruses, by themselves, cannot make or use food, grow or reproduce
    • Some scientists believe viruses were never independently living organisms
    • Others believe viruses evolved from simple bacteria like mycoplasmas & rickettsiae
    • Another hypothesis: viruses are genes that have escaped from the genomes of living cells
    • Not much evidence to support any one of these
  • 60. Beyond Viruses
    • Viroids
      • even smaller & simpler than viruses
      • cause some plant diseases
      • short pieces of RNA with no protein coat
    • Prions
      • Infectious agents that lack nucleic acids
      • “ protein only”
      • BSE
  • 61. Prion Action