Lecture 2 - Prokaryotes and the Origins of Metabolic Diversity
Chapter 27

I. Diversity of Prokaryotic Life

A. Common morphology - Fig. 27.2, and 3.1 in Lab Atlas

1. Spherical prokaryotes

a. cocci - single

b. diplococci - paired

c. streptococci - chains of many cells

d. staphylococci - clusters, resembling buchnes of grapes

2. Rod shaped

a. bacilli - single

b. diplobacilli - paired

c. streptobacilli - chain

3. Other shapes

a. spirilla/spirochetes - helical

b. vibrio - curved/bent

B. Cell surfaces

1. Gram positive - outermost layer is a peptioglycan (modified sugar polymers crosslinked with short polypeptides) - Fig p. 505

2. Gram negative - outer layer is a lipopolysaccharide (carbohydrates bound to lipids)

3. Capsule - additional outer layer, adhesive/protective

4. Pili - appendages which allow bacteria to become even more sticky

5. Endospore - tough, durable wall which can withstand extreme conditions

II. Prokaryotic nutrition

A. Major modes of nutrition - Table 27.1, know the definitions

- need two things, a source of energy (to generate ATP) and a source of carbon (for building organic molecules)

- Autotroph = needs only CO2 as a carbon source

- Heterotroph = needs at least simple sugars with which to build.

1. Photoautotrophs -(photosynthetic)

Energy - light

Carbon source - CO2

2. Chemoautotrophes

Energy - inorganic chemicals (H2S, NH4)

Carbon source - CO2

3. Photoheterotrophs (very few life forms)

Energy - light

Carbon source - organic compounds

4. Chemoheterotrophes

Energy - Organic compounds

Carbon source - organic compounds

B. Nutritional diversity (chemoheterotrophes)

1. saprobes - decomposers, get C from dead organic matter (chemoheterotrophes)

2. parasites - absorb nutrients from the body fluids of living hosts (chemoheterotrophes)

3. nitrogen fixation - bacteria convert atmospheric N2 into NH3. Only mechanism for the conversion of atmospheric nitrogen (abundant) into a form that can be bound into organic compounds (N often limiting - think plants). Chemoheterotrophes & photoautotrophes (cyanobacteria)

C. Metabolic relationships with oxygen

1. Obligate anaerobes- require a lack of oxygen

2. Facultative anaerobes - can survive in the presence of oxygen but don't use it

3. Obligate aerobes- require the presence of oxygen

III. Phylogenetic classification of prokaryotes - Fig. 27.11

A. Molecular systematics - use of base-pair sequences which are specific to given taxa to categorize groups of organisms

** simple phylogenetic tree

B. Domain Archea (Archaebacteria) -thought to be the most common ancestor of eukaryotic life

1. Methanogens - H2 used to reduce CO2 to CH4 (methane) - chemoautotroph, obligate anaerobes, swamps, sewage treatment

2. Extreme halophytes - extremely salty places

3. Extreme thermophiles - heat - hot springs, hydrothermal vents; chemoautotrophes, oxidize sulfur

C. Domain Bacteria (Eubacteria) - Table 25.3 many major phylogenetic groups, I'll just name a few.

1. Proteobacteria - most divers group - make a living in any of the four ways we have discussed previously: photoherterotrophic, photoautotrophic, chemoheterotrophic, chemoautotrophic

2. Cyanobacteria - photoautotrophic (photosynthetic), precursors to plants

3. Gram positive bacteria - contains positive and negative bacteria, chemoheterotrophes

a. Positive - many common bacteria (i.e. staphallococcus)

b. Negative - contains many of the more dangerous disease causing bacteria (i.e. causing salmonella and typhoid)

4. Chlamydias, chemoheterotrophes

- obligate intracellular parasite

- most common sexually transmitted disease in US, most common cause of blindness worldwide.

5. Spirochetes helical shape, corkscrew-like movement, chemoheterotrophes

- cause Lyme disease and syphilis

IV. Prokaryotes and disease

A. Pathogenic prokaryotes - harmful, disease causing

B. Opportunistic prokaryotes - present all the time, but can cause illness if health of host deteriorates, can become pathogenic

C. Exotoxin - secreted by prokaryotes, among the most toxic substances on the Earth, can produce disease symptoms without the bacteria even being present.

1. Clostridium botulinum - exotoxin causes botulism, one gram of this toxin could kill a million people.

2. Vibrio cholera - exotoxin causes cholera

D. Endotoxin - not secreted, but part of the make-up of the outer membranes of certain gram negative bacteria

1. Salmonella typhi - typoid fever

2. Salmonella sp. - food poisoning