Medical[DM1] Microbiology: Chapter 11
Characterizing and Classifying Prokaryotes
I. General Characteristics of Prokaryotic Organisms
A. Prokaryotes
1. Most diverse group of cellular microbes
2. habitats
a. from Antarctic to thermal hot springs
b. from colons of animals to cytoplasm of other prokaryotes
c. from distilled water to supersaturated brine (saltwater)
d. from disinfectant solutions to basalt rocks
3. only a few capable of colonizing humans/causing disease
B. Reproduction
1. all reproduce asexually
2. 3 main methods
a. binary fission (most common)
b. snapping division
c. budding
C. arrangement of prokaryotic cells
1. pairs – diplo
2. long chains – strepto
3. tetrads – four
4. sarcinae – eight
5. clusters – staphylo
D. Endospores
1. produced by gram+Bacillus and Clostridium
2. each vegetative cell transforms into one endospore and back
3. defensive strategy against unfavorable conditions
4. concern to food processors, health care professionals, governments
II. Modern Prokaryotic Classification
A. currently based on genetic relatedness of rRNA sequences
B. 3 domains
1. Archaea
2. Bacteria
3. Eukarya
III. Survey of Archaea
A. Common features
1. lack true peptidoglycan
2. cell membrane lipids have branched hydrocarbon chains
3. AUG codon codes for methionine
B. 3 phyla
C. reproduce by binary fission, budding, or fragmentation
D. most are cocci, bacilli, or spiral forms; pleomorphic forms exist
E. not known to cause disease
F. extremophiles
1. require extreme conditions to survive
-temperature, pH, and/or salinity
2. prominent members are thermophiles and halophiles
a. thermophiles – donot function below 450C
b. halophiles – inhabit extremely saline habitats
c. methanogens – obligate anaerobes
-largest group of archaea
-produce methane gas
-covert organic wastes in pond, lake, ocean, swamp, bog sediment to methane
-some live in colons of animals
IV. Survey of Bacteria
A. Deeply branching and phototrophic bacteria
1. deeply branching bacteria
a. scientists believe these organisms are similar to earliest bacteria
b. autotrophic
c. live in habitats similar to those thought to exist on early earth
2. phototrophic bacteria
a. divided into 5 groups
-blue-green bacteria (cyanobacteria)
-green sulfur bacteria
-green nonsulfur bacteria
-purple sulfur bacteria
-purple nonsulfur bacteria
B. Low G+C gram+bacteria
1. G (guanine)+C (cytosine) ratio – below 50%
2. Clostridia
a. rod-shaped, obligate anaerobes
b. important in medicine and industry
c. microbes related to Clostridium include sulfate-reducing microbes and Veillonella
d. examples:
-C. botulinum- botulism
-C. tetani- tetanus
-C. difficile- diarrhea
3. Mycoplasmas
a. facultative or obligate anaerobes –
b. lack cell walls
c. smallest free-living cells
d. examples
-pneumonia and urinary tract infections
4. Low G+C bacilli and cocci
a. Bacillus – many common in soil – anthrax, food poisoning
b. Listeria contaminates milk and meat products – bacteremia and meningitis
c. Lactobacillus – grows in body but rarely causes disease – yogurt and pickles
d. Streptococcus and Enterococcus – cause numerous diseases – strep
e. Staphylococcus – one of most common inhabitants of humans – staph
C. High G+C gram+ bacteria
1. Corynebacterium
a. pleomorphic aerobes and facultative anaerobes - diphtheria
b. produces metachromatic granules
2. Mycobacterium
a. aerobic rods that sometimes form filaments – tuberculosis (TB) and leprosy
b. slow growth partly due to mycolic acid in its cell walls
3. Actinomycetes
a. form branching filaments resembling fungi
b. important genera include Actinomyces, Nocardia, Streptomyces- in mouth;
makes antibiotics
D. Gram- proteobacteria
1. largest and most diverse group of bacteria
2. many have extensions called prosthecae
a. used for attachment and to increase surface area of nutrient absorption
b. divide into 5 classes: alpha, bet, gamma, delta, and epsilon
3. alphaproteobacteria
a. nitrogen fixers – important in agriculture
-Azospirillum
-Rhizobium
-Rhodopseudomonas
b. nitrifying bacteria – convert nitrogen into nitrate
-Nitrobacter
c. purple nonsulfur phototrophs
d. pathogenic alphaproteobacteria
-Rickettsia – typhus and Rocky Mountain Spotted Fever
-Brucella- brucellosis
e. other alphaproteobacteria
-Acetobacter
-Gluconobacter
-Caulobacter
4. betaproteobacteria
a. pathogenic
-Neisseria – gonorrhea
-Bordetella – whooping cough
-Burkholderia – in lungs of Cystic Fibrosis patients
b. nonpathogenic
-Thiobacillus
-Zoogloea – for sewage treatment
-Sphaerotilus – bad for sewage treatment
5. gammaproteobacteria
a. purple sulfur bacteria
b. intracellular pathogens
-Legionellla – Legionnaire’s disease
-Coxiella – Q fever
c. methane oxidizers
d. glycolytic facultative anaerobe
-Family Enterobacteriaceae
e. pseudomonads
-Pseudomonas – ear infections, urinary tract infections, lung infections of cf patients
-Azotobacter
-Azomonas
6. deltaproteobacteria
a. Desulfovibrio
b. Bdellovibrio
c. Myxobacteria
7. Epsilonproteobactereia
a. Campylobacter –gastroenteritis
b. Helicobacter – gastric ulcers
E. Other gram- bacteria
1. Chlamydias
-Chlamydia – STD; neonatal blindness; pneumonia
2. Spirochetes
a. Treponema – syphilis
b. Borrelia – lyme disease
3. Bacteroids
a. Bacteroides – abdominal infections
b. Cytophaga – damage wooden boats, piers
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