Bacteria, Archaeans and Viruses
Chapter 19
Biology Concepts and Applications, Eight Edition, by Starr, Evers, Starr. Brooks/Cole,
Cengage Learning 2011.
19.1 Evolution of a Disease
 Billions of years ago the Earth’s sea was home to
bacteria and archaeans
 Viruses are non-living
• No chromosomes, ribosomes, or metabolic
machinery
• Can evolve because they have genes that mutate
HIV
 Human immunodeficiency virus
• Isolated 1980s, however first infected humans in the
early 1900s
• Two strains: HIV-1 and HIV-2
• HIV-1 evolved from simian immunodeficiency virus
that infects wild chimpanzees
• Hypothesis
• First infected human ate meat from a SIV-infected
chimp
• The spread
• 1966: Africa  Haiti
• 1969: Haiti  USA
HIV
 20 million people have died from AIDS and
about 3 million are infected with HIV
 Disease mechanism
• Virus infects and replicated inside white blood
cells (WBC)
• WBC die  decreased immune response
19.2 Viral Structure and Function
 Viruses are noncellular infectious particles that
cannot reproduce on their own
 Viruses infect a host cell; their genes and
enzymes take over the host’s mechanisms of
replication and protein synthesis
 Each type of virus has structural adaptations that
allow it to infect and replicate in hosts
• Bacteriophages  infect bacteria
Virus Structure
 A virus particle consists of a core of DNA or
RNA and a protein coat
 In some viruses, the coat is enveloped in some
of an infected cell’s plasma membrane
• Outer envelope forms as each new virus particle
is released by budding or lysis
 In bacteriophages and other complex viruses,
the coat has a sheath and other structures
Viral Structures
Five Steps of Viral Multiplication Cycles
Viral Multiplication Pathways
 Multiplication pathways vary greatly
 Two are common among bacteriophages
• Lytic pathway
• Lysogenic pathway
Lytic Pathway
 New virus particles are released by lysis
• Multiplication is rapid
• The host is killed
Lysogenic Pathway
 Virus enters a latent state that extends the cycle
• Host cell is not killed outright
 Viral nucleic acids integrate into host chromosome
• All host cell’s descendants inherit genetic material
• May be reactivated many generations later, causing
cell to enter lytic pathway
• Like tiny little bombs
Bacteriophage:
Lytic and Lysogenic Pathways
a Virus particle
binds, injects
genetic material.
DNA in
protein
coat
tail
fiber
a Viral DNA is inserted
into host chromosome
by viral enzyme action
sheath
b Chromosome
and integrated viral
DNA are replicated.
e Lysis of host cell lets
new virus particles escape.
Lytic
Pathway
d Accessory parts are
attached to viral coat.
c Viral proteins selfassembleinto a coat
around viral DNA.
Lysogenic
Pathway
b Host replicates
viral genetic material,
builds viral proteins.
d Viral enzyme
excises
viral DNA from
chromosome.
c Cell divides;
recombinant
DNA in each
daughter cell.
Fig. 19.13, p.313
Enveloped Virus: Herpes Multiplication
HIV
Replication
Cycle
19.3 Viral Effects of Human Health
 Pathogen  disease-causing agent
• Adenovirus  upper respiratory infection and the
common cold
• Viral gastroenteritis  stomach flu
• Human papillomavirus  genital warts, cervical cancer
• Chicken pox (children)  shingles in adults
• Influenza, mumps, and measles
 Emerging Disease (ex. AIDS)
• A disease that was previously unknown or has recently
begun spreading to a new region
• Mutation can result in a new disease (RNA virus’)
West Nile Virus
 Enveloped RNA virus that replicates in birds
 Mosquitoes carry the virus from host to host
• Mosquito is the vector
• Vector  animal that carries a pathogen form one
host to the next
 West Nile Virus can cause West Nile Fever
• 1% virus enters the nervous system  fatal
 1999 introduced to Western Hemisphere
 West Nile Virus is an endemic disease in the US
• Endemic  disease that persists at a low level in
a region or population
SARS – Sudden Acute Respiratory Syndrome
 Appeared in 2002 – China
• Initial virus infected Chinese horseshoe bats
• Became epidemic  disease outbreak limited to
one region
• Air travel resulted in a pandemic  outbreak of
disease that affects many separate regions and
poses a serious threat to human health
• In 9 mons SARS sickened 8,000 people in 37
countries, killing 774.
Influenza H5N1 and H1N1
 Flu in the winter months
 Mutations result in different flu viruses each year
 H5N1  Bird Flu
• 417 cases (2003-2009), 257 fatal (60%)
• Person to person transmission rare
 H1N1  swine flu
• Easily transmitted by a cough or sneeze
• Mexico 2009  severe respiratory symptoms
• Low death rates, antiviral drugs releases, vaccine
created
19.5 Viroids and Prions
 Viroids
• Small circles of noncoding RNA without a protein
coat
• Many cause disease in plants
 Prions  Mad Cow Disease
• Proteins that occur naturally in the vertebrate
nervous system, but can cause fatal disease
when they misfold
Key Concepts: NONCELLULAR
INFECTIOUS PARTICLES
 Viruses are noncellular particles that cannot
replicate themselves without taking over the
metabolic machinery of a host cell
 A protein coat encloses their DNA or RNA and a
few enzymes
 Some viruses become enveloped in membrane
when they bud from host cells
Key Concepts: NONCELLULAR
INFECTIOUS PARTICLES (cont.)
 Viroids and prions are even simpler than viruses
 Viroids are short sequences of infectious RNA
 Prions are infectious misfolded versions of
normal proteins
Characteristics of Prokaryotic Cells
 Single-celled bacteria and archaeans
 No nucleus or membrane-bound organelles
 Smallest, most widely distributed, numerous,
and metabolically diverse organisms
• Autotrophs and heterotrophs
19.5 Bacterial Structure and Function
 Spheres (cocci), rods (bacilli), spirals (spirilla)
Bacterial Cell Structures
 Typical surface structures
•
•
•
•
Cell wall
Outermost protective capsule or slime layer
One or more flagella
Pili
• Hairlike extension form the cell wall of some
bacteria
Bacterial Cell Structures
 Inside the cell
• Bacterial chromosomes
• Circle of double-stranded DNA that resides in the
bacterial cytoplasm
• Nucleoid
• Cytoplasmic region where prokaryotic
chromosomes lie
A Bacterial Cell
Flagella and Pili
Bacterial Nutrition Modes
•Photoautotroph 
•photosynthetic, use light energy to build organic
compounds form carbon dioxide and water
•Chemoautotroph 
•get energy by removing electrons from sulfides
•Photoheterotroph 
•use light energy to get carbon by breaking down
organic compounds
•Chemoheterotroph 
•get carbon and energy by breakings down organic
compounds from other organisms
Bacterial Nutrition Modes
19.6 Bacterial Reproduction and Gene Exchange
 Only bacteria and archaeans reproduce by
binary fission:
• Replication of single, circular prokaryotic
chromosome
• Division of one parent cell into two genetically
equivalent daughter cells
• Asexual Reproduction
Prokaryotic Fission
a The bacterial
chromosome is
attached to the
plasma
membrane
prior to DNA
replication.
b Replication
starts and
proceeds in two
directions from
a certain site in
the bacterial
chromosome.
c The DNA copy
becomes
attached at a
membrane site
near the
attachment site
of the parent
DNA molecule.
d Then the two
DNA molecules
are moved
apart by
membrane
growth between
two attachment
sites.
e Lipids,
proteins, and
carbohydrates
are built for
new membrane
and new wall
material. Both
get inserted
across the
cell’s
midsection.
f The ongoing,
orderly
disposition of
membrane and
wall material at
the midsection
cuts the cell in
two.
Fig. 19.4, p.307
Gene Exchange Between Prokaryotes
 Horizontal gene transfers can transfer genetic
material between prokaryotes (bacteria and
archaeans)
 Conjugation moves a plasmid and some
chromosomal genes into another cell through a
sex pilus
• Plasmid  a small ring of nonchromosomal DNA
replicated independently of the chromosome
Review: Prokaryotic Cell Characteristics
Key Concepts:
DISTINCTLY PROKARYOTIC FEATURES
 We divide all prokaryotic cells into domains
Bacteria and Archaea
 Structurally simple, single-celled organisms
• Don’t have a nucleus or the diverse cytoplasmic
organelles found in most eukaryotic cells
 Collectively, they show great metabolic diversity
Key Concepts:
PROKARYOTIC FEATURES (cont.)
 Only bacteria and archaeans reproduce by
binary fission
 Exchanges of chromosomal DNA and plasmid
DNA often occur within and among species
19.7 Bacterial Diversity
 The most common and diverse prokaryotes
• Some are pathogens (cause disease in a host)
Bacterial Diversity: Heat-loving
 Modern heat-loving bacteria may resemble early
cells that emerged in thermal pools
 Near the base of the bacterial family tree
 One species discovered in a volcanic spring in
Yellowstone National Park
Bacterial Diversity: Cyanobacteria
 Oxygen-releasing photoautotrophs
• Release oxygen by noncylic pathways, as plants do
• Chloroplasts probably evolved from ancient
cyanobacteria by endosymbiosis
Bacterial Diversity: Cyanobacteria
 Oxygen-releasing photoautotrophs
• Heterocysts carry out nitrogen fixation 
Incorporation of nitrogen gas into ammonia
• Plant and algae can take up ammonia produced
and released by cyanobacteria to retrieve the
nitrogen they need
Bacterial Diversity: Proteobacteria
 The most diverse bacterial group
• Include autotrophs and heterotrophs, free-living
species, beneficial symbionts, and pathogens
• Escherichia coli
• Chemoheterotroph that live in the mammalian gut
• Normal flora
• Normally harmless or beneficial microorganisms
that typically live in or on a body
• Heliobactor pylori  stomach ulcers
• Vibrio cholerae  cholera
Bacterial Diversity: Proteobacteria
 The most diverse bacterial group
• Example: Thiomargarita namibiensis
• Chemoautotroph stores nitrogen and sulfur in huge
vacuole
Bacterial Diversity:
Gram-Positive Bacteria
 Most are chemoheterotrophs
• Ex. Lactobacillus  lactate fermentor (yogurt, cheese)
• Some are human pathogens
 Have thick walls
• Gram staining
• The process used to prepare bacterial cells for
microscopy, and to distinguish groups based on cell
wall structure
Gram Stain
Pink – cyanobacteria and
proeobacteria
Purple
DNA
spore
coat
capsule
around
cell wall
Fig. 19.7, p.309
Bacterial Diversity:
Gram-Positive Bacteria
 Have thick walls
• Endospores resist heat, boiling, irradiation, acids and
disinfectants
• Endospore is a resistant resting stage of some soil
bacteria
Bacterial Diversity:
Gram-Positive Bacteria
 Gram positive soil bacteria that form endospores
• Clostridium botulinum
• Anaerobe botulism  paralyzing food poisoning
• Clostridium tetani
• Tetanus  lock muscles in contraction
• Bacillus anthracis
• Anthrax  toxin interferes with breathing
 Other Gram-Positive Bacteria
• Mycobacterium tuberculosis  tuberculosis
• Strephtococcus  Strept throat
• Staphlococcus  boil or skin abscess
Bacterial Diversity: Chlamydias
 Chlamydias
• All are intracellular parasites of eukaryotic cells
• Obtain ATP from host cells
• Some sexually transmitted diseases (C.
trachomatis)
Bacterial Diversity: Spirochetes
 Spring-shaped  resemble a stretched-out spring
• Live on their own or in hosts
• Some are pathogens (Syphilis, Lyme disease)
19.8 The Archaeans
 Archaeans are prokaryotic, but like eukaryotic
cells in certain features
 Comparisons of structure, function, and genetic
sequences put archaeans in a separate domain,
between eukaryotes and bacteria
 Archaeans are more diverse and widely
distributed than previously thought
Three Archaean Groups
 On the basis of their physiology, archaeans fall
into three groups
• Methanogens
• Extreme halophiles
• Extreme thermophiles
Three Archaean Groups
 Methanogens
• Organisms that produce methane (CH4)
• Adapted to anaerobic conditions
• Exposure to oxygen inhibit their growth or kills
them
• Live near deep sea vents, in soil, in ocean
sediments.
• Live in human and animal guts and gas is
released by flatulence
Three Archaean Groups
 Extreme halophiles
• Highly salty environments
• Live in Dead Sea, The Great Salt Lake
 Extreme thermophiles
• High temperature
• Live in Hot springs and near deep sea vents
(temp 110oC/230oF)
Archaean Physiology
 Halophiles (salt lovers), extreme thermophiles,
and methanogens (methane makers)
Archaeans in Extreme Environments
Key Concepts:
THE PROKARYOTIC LINEAGES
 Bacteria are the most studied prokaryotic
species
 They are the most abundant and widely
distributed organisms
 Archaeans, discovered more recently, are less
well known
 Many are adapted to extreme environments
Evolution and Disease
 Hosts coevolve with pathogens
• Hosts evolve defenses
• Pathogens evolve to not kill a
host before they can infect
other host individuals
Mycobacterium
tuberculosis
SARS virus
Ebola virus
p.315
Antibiotic Resistance
 Use of antibiotics favors antibiotic-resistant
bacteria
 Genes that convey drug resistance can arise by
mutation, may spread among members of the
same or different species by conjugation
Deadly Pathogens
 Diseases can be fatal
• If an individual becomes host to multiple
pathogens
• If an individual has no coevolved defenses
• If a pathogen mutates into a different form that
can breach current defenses
 Two deadly emerging pathogens
• Ebola and the H5N1 strain of bird flu
Deadliest Infectious Diseases
Key Concepts:
THE BAD BUNCH
 An immense variety of pathogens, or diseasecausing agents, infect human hosts
 Pathogens and their hosts have been coevolving
by way of natural selection
Animation: Bacteriophage multiplication
cycles
Animation: Body plans of viruses
Animation: Examples of Bacteria
Animation: Gram staining
Animation: Lysogenic pathway
Animation: Lytic pathway
Animation: Prokaryotic body plan
Animation: Prokaryotic conjugation
Animation: Binary fission