Transcript Microbes: the most successful creatures on earth?

Microbes:
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the most successful creatures on earth?
• Is evolution driving towards perfection or greater
complexity?
– Prokaryotes are the simplest form of what scientists usual
consider life.
– Prokaryotes have been around for 3.8 billion years and
they are still here!
– So what’s the most successful form of life?
Why you think bacteria are simple
• Prokaryotic cells are only a fraction of the size of
eukaryotes
– Most bacteria are 1 – 5 µm in size; eukaryotes are 25x
that size.
– Bacteria have no internal organelles
• No nucleus (but yes, DNA), no mitochondria, no
endoplasmic reticulum (but they do have ribosomes)
• We are smarter
– We can kill them with disinfectants and antibiotics
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Why bacteria are more clever than you
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• Nutrition
– Give E. coli a simple nutrient source with mineral salts to
supply N, P, S, and other elements, and only glucose as
source of C, H, and O and it will grow.
• You would die. You need:
• 8 different amino acids
• Vitamins (A, many B vitamins, C, D, etc.)
• Habitat
– Different bacteria can live in places with extremes in pH,
temperature, with and without oxygen
How are bacteria classified?
• Taxonomy of cellular creatures
– Three domains
• Eubacteria: prokaryotic cell structure
• Archaebacteria: prokaryotes, but different
• Eukaryotes: 4 kingdoms
– Prokaryotes look alike
• Archaea and eubacteria very similar
• Differences are genetic, biochemical, and ecological
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Why Study Microbes?
Major impact on health
•Responsible for disease in humans, animals, plants
•Major impact on environment
•Major decomposers
•Nutrient cycling, elemental cycling
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Microbes are talented
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Live under extreme conditions
Protect against disease
Eat oil, toxic waste (bioremediation)
Make plastic
Spoil food, make food
Use light, produce light
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Bacterial Appearance
• Size
– 0.2 µm – 0.1 mm
– Most 0.5 – 2.0 µm
•Shape
Coccus (cocci); rod (bacillus, bacilli); spiral shapes;
filamentous; various odd shapes.
•Arrangement
Clusters, tetrads, pairs, chains
http://smccd.net/accounts/case/biol230/ex3/bact.jpeg
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How are bacteria put together?
• A cell membrane
– Separates inside from outside
• Cytoplasm
– No organelles
– Nucleoid instead of nucleus
– Ribosomes
• Cell wall (usually)
– In Eubacteria, made partly of peptidoglycan
• Outer layers
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Overview of
prokaryotic cell.
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Division of the Eubacteria:
Gram Negative and Gram Positive
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• Gram stain invented by Hans Christian Gram
– Gram positive cells stain purple; Gram negatives, pink.
• Architecture:
– Gram positives have a thick peptidoglycan layer in the
cell wall;
– Gram negatives have a thin peptidoglycan layer and an
outer membrane.
• Stain is valuable in identification.
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Gram Negative
Gram Positive
http://www.conceptdraw.com/s
ampletour/medical/GramNegat
iveEnvelope.gif
http://www.conceptdraw.com/s
ampletour/medical/GramPositi
veEnvelope.gif
Function and Structure of peptidoglycan
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• Provides shape and structural support to cell
• Resists damage due to osmotic pressure
• Provides some degree of resistance to diffusion of
molecules
• Single bag-like, seamless molecule
• Composed of polysaccharide chains cross linked with short
chains of amino acids: “peptido” and “glycan”.
• Many antibiotics work by preventing bacteria from
producing this cell wall material.
Bacteria and Osmotic pressure
• Bacteria typically face hypotonic
environments
– Insides of bacteria filled with proteins, salts, etc.
– Water wants to rush in, explode cell.
• Peptidoglycan provides support
– Limits expansion of cell membrane
– Growth of bacteria and mechanism of penicillin
• Bacteria need different protection from
hypertonic situations
– Water leaves the cell; cell membrane shrinks
– Lack of water causes precipitation of molecules,
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Effect of osmotic pressure on cells
• Hypotonic:
water rushes in;
PG prevents cell
rupture.
• Hypertonic:
water leaves
cell, membrane
pulls away from
cell wall.
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Glycocalyx: capsules and slime layers
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“Sugar covering”: capsules are firmly
attached, slime layers are loose.
Multiple advantages to cells:
prevent dehydration
absorb nutrients
cell
capsule
protection from predators, WBCs
protection from biocides (as part of biofilms)
attachment to surfaces and site of attachment by others.
www.activatedsludge.info/ resources/visbulk.asp
Fimbriae and pili
Both are appendages made of
protein
Singular: fimbria, pilus
Both used for attachment
Fimbriae: to surfaces (incl. host
cells) and other bacteria.
Pili: to other bacteria for
exchanging DNA (“sex”).
www.ncl.ac.uk/dental/oralbiol/ oralenv/images/sex1.jpg
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Fimbriae and pili-2
http://www.mansfield.ohio-state.edu/~sabedon/006pili.gif
Flagella
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•Flagella: protein appendages for
swimming through liquid or across wet
surfaces.
•Rotate like propellers.
•Different from eukaryotic flagella.
www.ai.mit.edu/people/ tk/ce/flagella-s.gif
www.bmb.leeds.ac.uk/.../icu8/ introduction/bacteria.html
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Energy and nutrition
• Bacteria as a whole have several different
ways of obtaining carbon and energy
– Thus they are adapted to many types of
environments.
– Heterotrophs: use pre-existing organic molecules
• Get energy aerobically or anaerobically (or both)
– Some are autotrophs: get carbon from CO2
• Some get energy from light: photosynthetic
• Some oxidize inorganic minerals
– Play various roles in the cycling of different
elements on the planet; play different roles in food
Archaea vs. Eubacteria:
So what’s the difference?
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• Genetic
– Ribosomal RNA genes different
• Biochemistry
– Cell wall polymer not peptidoglycan, but similar
– Lipids in membranes unusual
• Ecology
– Tend to live in extreme environments
• Very anaerobic, very salty, very acidic and/or
very hot
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Eubacteria: little disease-causing monsters?
• Hardly. Most bacteria have never been grown
in a lab, never mind on your tissues.
– Live in soil, water, in association with other
organisms.
– Some do make you sick
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Bacterial diseases
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Staph infection, E. coli infection, Strep throat
Anthrax, tularemia, plague
Syphilis, gonorrhea, chlamydia infection
tuberculosis