1 Microbes : the most successful creatures on earth? Is evolution driving towards perfection or greater complexity? –Prokaryotes are the simplest form.

1Microbes: 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?

2Why 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

3Why bacteria are more clever than you

• 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

4How 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

5Why Study Microbes?

Major impact on health•Responsible for disease in humans, animals, plants

•Major impact on environment•Major decomposers•Nutrient cycling, elemental cycling

6Microbes are talented

– Live under extreme conditions– Protect against disease– Eat oil, toxic waste (bioremediation)– Make plastic– Spoil food, make food– Use light, produce light

7Bacterial Appearance• Size

– 0.2 µm – 0.1 mm – Most 0.5 – 2.0 µm

•ShapeCoccus (cocci); rod (bacillus, bacilli); spiral shapes; filamentous; various odd shapes.

•ArrangementClusters, tetrads, pairs, chains

http://smccd.net/accounts/case/biol230/ex3/bact.jpeg

8How 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

9Overview of prokaryotic cell.

10Division of the Eubacteria:Gram Negative and Gram Positive

• 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.

11

http://www.conceptdraw.com/sampletour/medical/GramNegativeEnvelope.gif

http://www.conceptdraw.com/sampletour/medical/GramPositiveEnvelope.gif

Gram Negative

Gram Positive

12Function and Structure of peptidoglycan

• 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.

13Bacteria 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, death

14Effect of osmotic pressure on cells

• Hypotonic: water rushes in; PG prevents cell rupture.

• Hypertonic:

water leaves cell, membrane pulls away from cell wall.

15Glycocalyx: capsules and slime layers

www.activatedsludge.info/ resources/visbulk.asp

capsule cell

“Sugar covering”: capsules are firmly attached, slime layers are loose.

Multiple advantages to cells:prevent dehydrationabsorb nutrientsprotection from predators, WBCsprotection from biocides (as part of biofilms)attachment to surfaces and site of attachment by others.

16Fimbriae and pili

www.ncl.ac.uk/dental/oralbiol/ oralenv/images/sex1.jpg

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”).

17Fimbriae and pili-2

http://www.mansfield.ohio-state.edu/~sabedon/006pili.gif

18Flagella

www.ai.mit.edu/people/ tk/ce/flagella-s.gif www.bmb.leeds.ac.uk/.../icu8/ introduction/bacteria.html

•Flagella: protein appendages for swimming through liquid or across wet surfaces.•Rotate like propellers.•Different from eukaryotic flagella.

19Energy 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 webs

20Archaea vs. Eubacteria:So what’s the difference?

• 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

21Eubacteria: 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

22Bacterial diseases

• Staph infection, E. coli infection, Strep throat• Anthrax, tularemia, plague• Syphilis, gonorrhea, chlamydia infection• tuberculosis