Download Viruses and Prokaryotes

Viruses and Prokaryotes
Chapter 21 Part 2
21.6 The Bacteria
 Bacteria are the oldest, most diverse, and most
abundant prokaryotic lineage
 Most are harmless or benefit us by releasing
oxygen, fixing nitrogen, or cycling nutrients
 Some bacterial chemoheterotrophs cause
disease in humans
Heat Lovers
 Thermophiles are an old lineage that live in
volcanic springs or deep-sea hydrothermal vents
 Heat-stable DNA polymerase from Thermus
aquaticus was used in the first polymerase chain
reactions
Cyanobacteria
 Chloroplasts evolved from ancient cyanobacteria
• Put oxygen in Earth’s atmosphere
 Nitrogen fixation
• Some cyanobacteria form heterocysts that fix
atmospheric nitrogen (N2) into ammonia (NH3)
resting spore
heterocyst
6 µm
Fig. 21-12, p. 342
Metabolically Diverse Proteobacteria
 Thiomargarita namibiensis strips electrons from
sulfur
 Helicobacter pylori causes stomach ulcers
 Magnetotactic bacteria detect magnetic fields
 Myxobacteria form multicelled fruiting bodies
Metabolically Diverse Proteobacteria
0.2 mm
Fig. 21-13a, p. 343
1 µm
Fig. 21-13b, p. 343
magnetite
Fig. 21-13c, p. 343
capsule with
resting cells
Fig. 21-13d, p. 343
The Gram-Positive Heterotrophs
 Gram-positive bacteria have thick walls that
stain purple by Gram-staining
• Thin-walled bacteria (Gram-negative) stain pink
 Lactobacillus fermentation reactions produce
yogurt and other foods
 Some form endospores in unfavorable
conditions, and make deadly toxins
• Anthrax, tetanus, botulism
Gram-Positive Bacteria
DNA
spore
coat
capsule
around
cell wall
Fig. 21-14b, p. 343
Spirochetes and Chlamydias
 Spirochetes are spring-shaped
• Example: Borrelia burgdorferi (pathogen that
causes Lyme disease) carried by ticks (vectors)
 Chlamydias are intracellular parasites
• Example: C. trachomatis, a common cause of
sexually transmitted disease
21.6 Key Concepts
The Bacteria
 Bacteria are the most abundant prokaryotic cells
on Earth
 Bacteria perform important services such as
degrading wastes, adding oxygen to the air, and
providing essential nutrients to plants
 Nearly all disease-causing prokaryotes are
bacteria
21.7 The Archaeans
 Archaeans, the more recently discovered
prokaryotic lineage, are the third domain – the
closest prokaryotic relatives of eukaryotes
 Archaeans live everywhere – many live in very
hot or very salty habitats
 Hardly any archaeans cause human disease
Archaean Physiology
 Methanogens (methane producers)
• Strict anaerobes
 Extreme halophiles (salt lovers)
• Aerobic or photosynthetic
 Extreme thermophiles (heat lovers)
• Chemoautotrophs or heterotrophs
Methanogenic Archaeans
0.5 µm
Life in Extreme Environments
Fig. 21-17a, p. 345
5 µm
Fig. 21-17b, p. 345
Fig. 21-17c, p. 345
Fig. 21-17d, p. 345
21.7 Key Concepts
The Archaeans
 Archaeans are the more recently discovered,
less studied prokaryotic group
 Some show a remarkable ability to survive in
extreme habitats, but others live in more
ordinary places
 They play important roles in ecosystems
21.8 Evolution and Infectious Disease
 Infection occurs when pathogens enter the
internal environment and multiply
 Disease follows when the pathogen’s activities
interfere with normal body functions
 Viruses, bacteria, and other pathogens evolve
by natural selection, as do their hosts
Deaths From Infectious Diseases
The Spread of Diseases
 Sporadic diseases
• Occur irregularly, affect few people
 Epidemic diseases
• Spread quickly, then subside
 Endemic diseases
• Occur continually, but don’t spread far
 Pandemic diseases
• Break out and spread worldwide
The SARS Epidemic
An Evolutionary Perspective
 Two barriers prevent pathogens from dominating
• Species that coevolve with specific pathogens
have built-in defenses
• A pathogen that kills its host too fast might
disappear along with the host
Emerging Diseases
 Animals in remote habitats carry dangerous
pathogens that have not coevolved with humans
• HIV, SARS, Ebola, and H5N1 avian influenza all
came from close contact with animals
• A bird flu caused the 1918 pandemic that killed
50 million people
The Threat of Drug-Resistance
 In a population of pathogens, drug-resistant
individuals survive and reproduce
• About half the known strains of Streptococcus
pneumoniae are penicillin resistant
• Many strains of HIV are now resistant to the
antiviral drugs used to fight them
It’s a Small World
 In this age of global air travel and constant
human migrations, it is difficult to contain the
spread of dangerous pathogens
Which is Deadlier?
 Ebola kills up to 90% of those infected, but is
sporadic; Mycobacterium tuberculosis kills 50%,
but is widespread and drug resistant
400 nm
Fig. 21-19a, p. 347
0.5 µm
Fig. 21-19b, p. 347
21.8 Key Concepts
Evolution and Disease
 An immense variety of pathogens, or diseasecausing agents, infect human hosts
 Pathogens and their hosts coevolve; each acts
as a selective agent on the other
Animation: Body plans of viruses
three major processes: conjugation,
transformation, and transduction
Animation: Enveloped DNA virus
replication
Animation: Examples of Eubacteria
Animation: Gram staining
Animation: Prokaryotic body plan
ABC video: Bird Flu
ABC video: Germs in Pakistan
ABC video: Mask of Technology
ABC video: AIDS Conference in Brazil
ABC video: Beach Pollution
ABC video: Polio Scare
ABC video: The Problem with Pork
ABC video: World AIDS Day
Video: The face of AIDS