Bacteria

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Bacteria Viruses
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By the end of this class you should understand

• How life may have arisen from nonliving materials
• Modern classifications of bacteria and familiar
  species we encounter every day
• The life cycle of parasitic protists
• How viruses work and whether they are alive
• How to protect yourself from bacteria and viruses

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Early Life on Earth

• Life first appeared around 3.8 billion years ago,
  soon after liquid water formed
• Not recognizable as modern life
• Fulfilled the basics of life
• Reproduced
• Took in energy
• Probably didnt maintain homeostasis very well yet

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Nonliving Synthesis

• Life is formed from large assemblies of
  macromolecules
• How could these have been assembled without life?
• There are a number of hypotheses on how these
  molecules could have been assembled
• Clay deposits that preferentially collect charged
  particles and then dried up
• Hydrothermal vents at the ocean floor naturally
  produce carbon molecules

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Protocells

• One way or another, these molecules eventually
  formed into protocells
• Protocells have been studied as a likely
  mechanism for a precursor to life
• Essentially, fatty acids collect into a simple
  membrane, and inside, enzymes made of RNA called
  ribozymes convert other molecules into RNA
• Cell grows as more RNA is absorbed and splits
  naturally

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Evidence for Protocells

• A lot of evidence exists that this mechanism is
  possible, but thats not the same thing as
  evidence that it actually happened
• The key evidence is protein synthesis
• Common to all life
• Uses RNA-based process (ribosomes and tRNA)

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Prokaryotes Revisited

• Modern bacteria are nothing like early bacteria
• Through natural selection, only the hardiest and
  fastest-reproducing bacteria were represented in
  the next generation
• Bacteria can ideally reproduce in 20 minutes
• One bacterium in a soup of nutrients can make a
  colony of 100 million bacteria in 12 hours

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Three Modern Domains of Life

• Archaea
• Bacteria that resemble early life
• Live in unusual environments
• Eubacteria
• What we think of as bacteria
• All pathogens are eubacteria
• Eukarya
• All eukaryotes including humans

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Archaea

• Oldest and least changed bacteria
• Many live in hostile environments
• Extremely acidic
• Deep ocean vents
• Boiling hot springs (extreme thermophiles)
• Salt marshes (extreme halophiles)
• Oil wells
• Others live in more normal environments

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Eubacteria

• Most bacteria that we are familiar with
• Many are harmless or even helpful
• Bacteria that live on our skin and in our gut are
  called normal flora and they crowd out more
  dangerous bacteria
• Some are dangerous to our health
• Usually eat our tissues for nutrients
• Some release dangerous toxins instead

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Classifications of Eubacteria

• Gram staining
• Gram positive turn purple in a Gram stain
• Has a cell membrane and a crunchy cell wall
• Gram negative stay pink in a Gram stain
• Has two cell membranes with a wall between

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Another Classification

• Aerobic
• Aerobic bacteria can survive in air
• Many bacteria on the skin
• Mitochondria are related to early aerobic
  bacteria
• Anaerobic bacteria
• Die when exposed to air
• Lack catalase and peroxidase enzymes
• Many bacteria in your gut and that spoil food

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How do anaerobes get around?

• Solution spores!
• Some bacteria create spores in harsh conditions
• These spores can survive almost anything
• Turn back into bacteria when the conditions have
  improved

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Bacteria shapes

• Coccus sphere
• Bacillus rod
• Spirillum spiral
• Many other weirder shapes also exist
• Often in the bacteria name

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Staphylococcus

• Gram positive
• Common on human skin, usually harmless
• Some are harmful
• Infections
• Food poisoning
• Responsible for Staph infection

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Streptococcus

• Gram positive
• Many also found on human skin
• Dangerous strains responsible for strep throat
• Even more dangerous types cause Scarlet fever
• Most dangerous is flesh-eating bacteria
• Pictures not provided for the faint of stomach

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Escherichia coli

• E. coli
• Gram negative
• Common in human digestive tract
• Helpful for metabolism
• Some virulent strains exist
• E. coli outbreaks are really Rare and
  dangerous strain of mutated E. coli outbreak
• Often not the bacteria that is harmful but the
  toxins it produces

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Salmonella

• Gram negative
• Commonly found in humans and farm animals
• Can cause food poisoning in undercooked poultry
  products
• Other species cause typhoid fever
• Infect human cells using a capsule
• Potentially lethal

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Antibiotics

• Antibiotics are chemicals that selectively kill
  bacteria and not eukaryotic cells
• Ineffective against human, yeast, and protozoa
• Effective against certain types of bacteria only
• Penicillin was the first antibiotic that killed
  all Gram-positive bacteria
• Ampicillin and Streptomycin kill all bacteria

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Antibiotic resistance

• Bacteria constantly mutate and develop new genes
• Bacteria also pass genes to each other on
  plasmids, small rings of DNA
• As a result, bacteria may develop a resistance to
  an antibiotic, so taking antibiotics regularly is
  generally inadvisable
• Additionally, antibiotics kill the normal flora
  of your intestines and possibly your skin

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Better the devil you know...

• MRSA (methicillin-resistant Staph aureus) is very
  dangerous
• Can have many resistance plasmids
• Becoming increasingly common in hospitals
• Best defense is a healthy immune system and
  normal flora

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This is a real problem
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Protists

• Protists are eukaryotic single-celled organisms
• Amoebas, paramecium, etc.
• Many probably resemble early eukaryotes
• I will not be covering most of the protists since
  there are approximately a hojillion of them, but
  I will cover Plasmodium, the protist that causes
  malaria
• Because Im friendly like that!
• Most protists are NOT infectious

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Malaria Life Cycle
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Virus

• A virus is a nonliving infectious particle that
  uses genetic information to reproduce
• All viruses reproduce by injecting their genetic
  molecules into a host cell
• The genetic molecules (DNA or RNA) force the cell
  to make more viruses
• Viruses have no metabolism of their own and do
  not maintain homeostasis or reproduce
  independently

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Parts of a Virus

• All viruses have
• Protein coat
• Spikes that target host cell
• Genetic material
• Some viruses have a membrane called an envelope

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What about these weirdos?

• This is a bacteriophage
• Virus that infects bacteria
• Useful in scientific research
• Keeps its DNA in the capsule, injects it through
  the tube into the bacteria
• Bacteria have enzymes that try to chop up DNA
  that doesnt belong, so its an ongoing arms race!

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What does the genetic info do?

• Sample HIV in human cell
• Essentially the DNA or RNA causes the cell to
  make more viral proteins
• The viruses are exocytosed or bud off with
  envelope until the cell dies

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Host specificity

• The virus spikes can only latch onto certain
  receptors
• This keeps viruses from freely moving between
  different species of animals
• Crossover occurs due to mutation, e.g. bird flu
• Viruses can only infect certain cells in the host
• HIV only infects Helper T cells
• Rhinovirus infects epithelial cells
• Some viruses (e.g. herpes) infect nerve cells
• These are generally incurable

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Antibiotics NOT for Viruses

• Do NOT take antibiotics for viruses
• Not only will it do nothing, it exposes you to
  potential bacterial infections to go with your
  viral infection!
• Vaccines are available for some viruses
• A vaccine is a piece of a bacterium or virus that
  your immune system learns to kill
• Pre-training your immune system so you dont get
  the same disease again
• Many viruses and some bacteria mutate too quickly
  to have effective vaccines made!

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Protip

• VACCINES DO NOT CAUSE AUTISM
• There was a time when vaccines were packaged with
  an antiseptic called thimerosal, which is a
  mercury-containing compound
• They are no longer packaged as such
• The original study linking vaccines and autism
  was discredited, and many scientists have
  repeated the experiment but found no
  statistically significant difference
• Autism is a developmental disorder and more
  prevalent in males, it cannot be caused by an
  injection at six months of age

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See you in lab!