BI113 General Biology II Lecture 10

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BI-113 General Biology IILecture 10

• Viruses and Bacterial Diversity

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Wendell Stanley

• 1933
• Discovers chemical-like nature of viruses by
  precipitating tobacco mosaic virus

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Viruses

• What are they?
• Non-cellular
• NO nucleus or organelles
• Do NOT metabolize
• Do NOT respond to stimuli
• Pieces of genetic material (RNA or DNA)
• May be single strand or double
• Surrounded by a protein coat (capsid)
• Small - less than 200 nm (10-9 meters) in
  diameter
• Intracellular parasites
• Cannot multiply outside of host cells

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Viral Structure
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Viruses are not living

• But they do replicate themselves and do evolve
  (change genetic material over time)
• Two cycles of replication
• Lytic cycle
• Normal viral replication
• Lysogenic cycle
• Latent replication
• Viral DNA is spliced into the host DNA, may
  become active later and enter lytic cycle to
  produce more viruses

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Lytic cycle
5. Release - new viral particles are released
when cell ruptures
1. Attachment - viral capsid bonds to cell
membrane receptor
4. Maturation - viral components are assembled
2. Penetration - viral genome enters host
cytoplasm
3. Biosynthesis - viral components are
synthesised by host
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Viral Pathogens

• Incorporation of viral genome into host material
  (RNA or DNA)
• Phage conversion
• Viral genome high jacks host cellular machinery
  and disrupts normal cell function
• Major viral diseases
• Chicken pox, measles, mumps - childhood
  occurrence
• Influenza - major killer, historically new
  strains
• Rabies - transmitted by infected bite
  encephalomyelitis
• AIDS - immune system effects leave victim
  susceptible to other conditions
• Ebola - acute hemorrhagic fever high rate of
  mortality
• Polio - central nervous system attack leads to
  paralysis/death

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Kingdom - Monera

• The Bacteria and their close relatives
• Eubacteria - True bacteria
• Lack nuclei, organelles and cytoskeletal elements
• DNA as single, circular chromosome may also have
  plasmids (small, circular DNA strands)
• May have membrane infoldings (mesosomes) that
  serve as sites for photosynthesis
• Very ancient group (known from Precambrian
  fossils)
• Show great diversity of kinds and enormous
  populations
• Many generations in short period of time
• Taxonomy presents many problems
• Need more information

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Classification of bacteria

• Cell Shape
• Coccus
• Spherical
• Bacillus
• Rod-shaped
• Spirillum
• Spiral

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Classification of bacteria

• Colony Morphology
• Often species specific

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Bacterial structure
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Bacterial cell wall composition

• A reflection of the Gram stain
• Developed by Hans Christian Gram (Danish
  physician - 1884)
• Gram positive with a thick peptidoglycan
  (complex polysaccharide) coat outside the plasma
  membrane
• Gram negative thin peptidoglycan layer with
  outer membrane and capsule of liposaccharides and
  lipoproteins

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Gram stain
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Metabolic diversity in bacteria

• Oxygen requirements
• Obligate anaerobes
• Can only survive in environments that do not have
  oxygen
• Facultative anaerobes
• Can live in either aerobic (with oxygen) or
  anaerobic conditions
• Obligate aerobes
• Cannot survive in conditions without oxygen

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Nutritional categories

• Photoautotrophs photosynthetic - light
  (photons) as source of energy CO2 as carbon
  source
• Photoheterotrophs light for energy, but carbon
  comes from carbohydrates, fatty acids, or
  alcohols (ethanol, etc.)
• Chemoautotrophs oxidize inorganic substrates
• Chemoheterotrophs obtain energy and carbon from
  organic source

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Nitrogen metabolism

• Utilize nitrogen as an electron acceptor in
  metabolism
• Denitrifiers
• Return N2 to the atmosphere as the result of
  nitrate (NO3-) utilization
• Nitrogen Fixers
• Convert atmospheric N2 into compounds (NH3) that
  can be used for the formation of proteins and
  nucleic acids

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More nitrogen-using bacteria

• Nitrifiers - gain chemical metabolic energy by
  converting ammonia (NH3) to nitrite (NO2-) and/or
  nitrate (NO3-).
• Nitrosomonas and Nitrosococcus
• Nitrobacter - can convert CO2 to glucose using
  nitrite
• 6 CO2 78 NO2- C6H12O6
• This is why ammonia is used as a fertilizer in
  agriculture - soil bacteria take the ammonia,
  convert it to nitrogen forms that can be used by
  plants

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Other bacterial traits

• Sulfur metabolism - utilize sulfur-containing
  molecules as an electron acceptor in metabolism,
  usually H2S
• Motility - via flagellae, but with different
  structure than encountered in animals
• Has single fibril made of the protein flagellin
• Asexual reproduction - but some forms transfer
  DNA via conjugation tube
• Fission
• Endospore formation

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Bacterial Motility
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Pathogenicity of Bacteria

• Ability to cause disease
• Robert Koch (1843-1910) German physician
• first to connect disease conditions with specific
  bacteria
• isolated anthrax and tuberculosis pathogens
• 1905 - Nobel Prize for Medicine

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Kochs Postulates

• Serve as guidelines for medical microbiology
• A disease could be attributed to a specific
  bacteria if
• The microorganism could always be found in
  diseased individuals
• The microorganism taken from the host could be
  grown in a pure culture
• A sample of the culture produced the same disease
  when injected into a new, healthy host
• The newly infected host yielded a new, pure
  culture of microorganisms identical to those
  obtained in earlier isolations

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Bacterial pathogenicity two factors

• Invasiveness - the ability to multiply and spread
  within the host
• Toxigenicity - the ability to produce chemical
  substances (toxins) that are harmful to the
  hosts tissues
• Endotoxins - chemical components of the cell wall
  that are released when certain Gram-negative
  bacteria are lysed. Rarely fatal, but cause
  fever, vomiting and diarrhea (ex., Salmonella and
  Escherichia)
• Exotoxins - proteins produced by living, dividing
  bacteria which travel through the hosts body.
  Highly toxic (often fatal), but do not cause
  fever (ex., tetanus, cholera, botulism)

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Bacteria get a bad rap

• It is important to remember that most bacteria
  are not pathogenic. Most are important organisms
  in the soil, leaf litter and other environmental
  situations. Many are utilized in beneficial ways
  - production of cheese and other products

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Eubacterial Classification - just an overview

• 10,000 species
• Actinomycetes fungal-like bacteria (were once
  classified as fungi)
• 40 genera
• Branched, filamentous morphology
• Gram positive
• Most live in soil and leaf litter
• Spore forming chains formed at ends of filaments

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Actinomycetes - good and bad

• Medically important group
• Source of many antibiotic drugs (streptomycin,
  erythromycin, aureomycin, and tetracycline all
  from Streptomyces)
• Antibiotic compounds formed during spore
  production - may be associated with reproduction
  (prevent competing growth of other bacteria and
  fungi)
• Actinomyces
• Normal flora of tonsils, mouth, gut and lungs,
  but can become invasive
• Mycobacterium tuberculosis
• Responsible for tuberculosis, a disease which is
  making a comeback in the US - 2.5 million
  deaths/year

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Chemoautotrophic bacteria

• 25 genera
• Utilize energy obtained by oxidizing inorganic
  substances (NH3, NO3-, H2S, S, Fe3) plus carbon
  from CO2 to build organic molecules
• Since O2 is terminal electron acceptor, these are
  obligate aerobes
• Common in aerated soil
• Nitrobacter and Nitrosamonas - nitrogen utilizing
  bacteria
• Thiobacter - sulfur utilizing bacteria

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Cyanobacteria Blue-green bacteria

• 32 genera
• Photosynthetic pigment is chlorophyll a (similar
  to eukaryotic photosynthesis)
• Thylakoids - photosynthetic lamellae
• Single, free living cells and colonial forms
• Heterocysts - specialized cells for fixation of
  Nitrogen (nitrogenase enzyme required), also
  serve reproductive function (breaking point for
  filamentous colonies)
• Many fresh-water species, but also marine and
  terrestrial species, some are symbiotic in
  lichens
• Anabaena (colonial, freshwater), Chroococcus,
  Nostoc (freshwater), Oscillatoria, and Spirulina

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Cyanobacteria
Anabaena sp.
Nostoc sp.
Oscillitoria sp.
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Endospore-forming bacteria

• 6 genera
• Gram positive, flagellated rod
• Produce endospores to survive harsh environmental
  periods
• Bacillus thuringiensis - biological control agent
  against insects
• Bacillus subtillus - common bacteria used in
  commercial production of bacitracin (an
  antibiotic)
• Bacillus cereus - food poisoning
• Clostridium tetani - tetanus
• Clostridium botulinum - botulism, toxin is the
  strongest known, one gram is sufficient to kill
  one million humans

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Endospores
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Enteric bacteria

• 34 genera
• Gram negative, facultative anaerobes
• Many metabolic pathways used
• Inhabit intestinal tract of animals
• Some are harmless, gut residents, others are
  pathogenic
• Escherichia coli - intestinal bacteria (resides
  in colon), problem comes when it gets into
  stomach
• Salmonella typhi - Typhoid fever
• Vibrio cholerae - cholera, causes a severe
  disruption of the intestine leading to diarrhea

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Enteric bacteria
Salmonella typhi
Vibrio vulnificus - an enteric pathogen in
shellfish
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Mycoplasmas

• 6 genera
• Smallest of all cells - 100-250 nm
• Lack cell walls
• Mycoplasma - is responsible for a number of
  pneumonia-like respiratory diseases, including
  upper respiratory tract disease (URTD) in
  tortoises
• This has been linked to population declines in
  wild desert tortoises (33-76 decline in turtles
  over ten years old)
• Known from populations of tortoises in SW US,
  Florida, and France

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Myxobacteria

• 8 genera
• Small, gram-negative rods
• Soil-dwelling chemoheterotrophs
• move by gliding
• In harsh conditions, cells congregate and form a
  fruiting body that releases spores these grow
  into new cells under favorable conditions
• Myxococcus

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Myxococcus fruiting structure
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Nitrogen-fixing aerobic bacteria

• 5 genera
• Azotobacter - free-living nitrogen fixer that
  lives in soil or water
• Rhizobium - mutualistic bacteria associated with
  nodules on the roots of legumes, supply nitrogen
  to plants

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Nitrogen fixation
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Phototrophic anaerobic bacteria

• 27 genera
• Photoautotrophs that are less plant-like than
  cyanobacteria in their photosynthetic systems
• Reduce NADP with electrons extracted from H2S
  (not H2O), do not release O2
• Found in pond, lake and ocean sediments strict
  anaerobes
• Chromatium
• Rhodospirillum

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Pseudomonads

• 5 genera
• Gram-negative, rod-shaped and flagellated
• Chemoheterotrophs with ability to use a variety
  of unusual nutrients
• Pseudomonas - diverse group found in water and
  soil

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Rickettsias and Chlamydias

• 15 genera
• Gram negative (but with reduced cell wall)
• Obligate intracellular parasites in animals
• Rickettsia - alternate between arthropod and
  human hosts
• Chlamydia cell walls lack peptidoglycan
• Disease spread from humans or birds

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Spirochetes

• 7 genera
• Helical cells, sometimes large (0.25 mm)
• Swim with corkscrew motion, due to internal
  flagellar filaments
• Free-living and parasitic (disease-causing) forms
• Borrelia - Lyme disease
• Leptospira - meningitis
• Treponema pallidum - syphilis

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Spirochetes
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Archaebacteria

• Three categories
• Kingdom Euryarchaeota
• Methanogens and Halophiles
• Kingdom Crenarchaeota
• Thermophiles
• Kingdom Korarchaeota
• Some Hot Springs Microbes

The vivid red brine (teaming with halophilic
archaebacteria) of Owens Lake contrasts sharply
with the gleaming white deposits of soda ash
(sodium carbonate).
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Euryarchaeota

• Methanogens
• Anaerobes
• Live in environments without oxygen
• Swamps, marshes and mammalian intestines
• 2 billion tons of methane produced annually
• 4 H2 CO2 CH4 2 H2O
• Halophiles - salt lovers

These pinkish-red crystals of sodium chloride
(NaCl) are colored by millions of
halobacteria. The bacteria survive inside the
salt crust, even though it has been exposed to
sun-baked summers and freezing winters in
California's Owens Valley.
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Crenarchaeota

• Thermophiles - heat lovers
• Deep-sea vents, geysers, and hot springs
• 60 to 115 C
• Sulfur metabolism
• Hydrogen sulfide
• pH-tolerant
• Acidic hot springs
• pH lt 4.0
• Algae (Cyanidium caldarum) and archaea
• Pressure tolerant

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Archaebacterial Environments
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Archaebacterial Environments