CHAPTER 27
BACTERIA and ARCHAEA
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OVERVIEW
1. Earliest organisms on Earth
2. Dominate biosphere
3. Live everywhere
4. Commonly referred to as “bacteria”
5. Prokaryotic cells
6. Classified into two domains, Bacteria and Archaea, which
differ in structure, physiology, and biochemistry
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Bacteria on a Pin
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I. Concept 27.1: Structure, Function,
and Reproduction of Prokaryotes
A. Structure
1. Most are unicellular, although some species form
colonies
2. 3 major shapes
• coccus-spherical
• bacillus-rods
• spirillum- spirals (helices)
3. Groupings
• strepto—chains
• staphylo—clusters
• diplo—pairs
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3 Major Shapes of Bacteria
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B. Cell-Surface Structures
1. An important feature of nearly all prokaryrotic cells is their
cell wall—maintains cell shape, provides physical
protection, and prevents the cell from bursting in a
hypotonic environment
2. Eukaryote cell walls are made of cellulose or chitin
3. Bacterial cell walls contain peptidoglycan, a network of
sugar polymers cross-linked by polypeptides
4. Walls of archaea contain polysaccharides and proteins,
but lack peptidoglycan
5. Cell membrane is internal to cell wall and other
substances may be external to cell wall
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6. Using the Gram stain, scientists classify many
bacterial species into Gram-positive (stain blue) and
Gram-negative (stain pink or red) groups based on cell
wall composition
7. Gram-negative bacteria have less peptidoglycan and
an outer membrane that can be toxic, and they are
more likely to be antibiotic resistant
8. Many antibiotics target peptidoglycan and damage
bacterial cell walls
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Gram Positive/Gram Negative
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9. A polysaccharide or protein layer called a capsule
covers many prokaryotes
10. Some prokaryotes have fimbriae (also called
attachment pili), which allow them to stick to their
substrate or other individuals in a colony
11. Sex pili are longer than fimbriae and allow prokaryotes
to exchange DNA
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Capsule
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Fimbriae
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C. Motility
1. Most motile bacteria propel
themselves by flagella that are
structurally and functionally
different from eukaryotic flagella
2. In a heterogeneous
environment, many bacteria
exhibit taxis, the ability to move
toward or away from certain
stimuli (Ex: phototaxis,
chemotaxis, magnetotaxis)
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D. Internal and Genomic Organization
1. Prokaryotic cells usually lack complex compartmentalization
3. The prokaryotic genome has less DNA than the eukaryotic
genome
4. Most of the genome consists of a circular chromosome
3. Some species of bacteria also have smaller rings of DNA
called plasmids some can provide resistance to antibiotics
5. The typical prokaryotic genome is a ring of DNA that is not
surrounded by a membrane and that is located in a nucleoid
region
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Specialized Membranes of
Prokaryotes
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E. Reproduction and Adaptation
1. Prokaryotes reproduce quickly by binary fission and can
divide every 1–3 hours
2. Many prokaryotes form metabolically inactive endospores,
which can remain viable in harsh conditions for centuries
• Endospores are resistant cells that form when an
essential nutrient is lacking in the environment
• They replicate the chromosome and surround it with a
durable wall
• Original cell disintegrates and leaves the endospore
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3. Growth refers to increased number of cells and some
factors affecting growth include temperature, pH, salt
concentrations, and nutrient sources
4. Prokaryotes can evolve rapidly because of their short
generation times
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Endospore
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II. Concept 27.2: Genetic Diversity in
Prokaryotes
• Prokaryotes have considerable genetic variation
• Three factors contribute to this genetic diversity:
– Rapid reproduction
– Mutation
– Genetic recombination
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A. Rapid Reproduction and Mutation
1. Prokaryotes reproduce by binary fission, and offspring cells
are generally identical
2. Mutation rates during binary fission are low, but because of
rapid reproduction, mutations can accumulate rapidly in a
population
3. High diversity from mutations allows for rapid evolution
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B. Genetic Recombination
1. Additional diversity arises from genetic recombination
2. Prokaryotic DNA from different individuals can be brought
together by transformation, transduction, and conjugation
3. A prokaryotic cell can take up and incorporate foreign DNA
from the surrounding environment in a process called
transformation
4. Transduction is the movement of genes between bacteria
by bacteriophages (viruses that infect bacteria)
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TRANSDUCTION
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TRANSDUCTION
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5. Conjugation and Plasmids
• Conjugation is the process where genetic material is
transferred between bacterial cells
• Sex pili allow cells to connect and pull together for
DNA transfer
• A piece of DNA called the F factor is required for the
production of sex pili
• The F factor can exist as a separate plasmid or as
DNA within the bacterial chromosome
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CONJUGATION
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6. The F Factor as a Plasmid
• Cells containing the F plasmid function as DNA donors
(male) during conjugation
• Cells without the F factor function as DNA recipients
(female)during conjugation
• The F factor is transferable during conjugation and when
transferred converts the female to a male
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Conjugation—F Plasmid
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7. The F Factor in the Chromosome (Hfr male)
• A cell with the F factor built into its chromosomes
functions as a donor during conjugation
• The recipient becomes a recombinant bacterium, with
DNA from two different cells
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CONJUGATION—Hfr Male
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8. R Plasmids and Antibiotic Resistance
• R plasmids carry genes for antibiotic resistance
• Antibiotics select for bacteria with genes that are
resistant to the antibiotics
• Antibiotic resistant strains of bacteria are becoming
more common
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III. Concept 27.3: Nuttitional and
Metabolic Adaptations
 Greater diversity in prokaryotes than in all other kingdoms
combined.
A. 4 Major Modes of Nutrition:
1. Phototrophs obtain energy from light
2. Chemotrophs obtain energy from chemicals
3. Autotrophs require CO2 as a carbon source
4. Heterotrophs require an organic nutrient to make
organic compounds
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B. These factors can be combined to give the four major
modes of nutrition:
photoautotrophy (cyanobacteria, plants and algae)
chemoautotrophy (probably earliest prokaryotes and
unique to prokaryotes)
photoheterotrophy (a few marine and halophilic
prokaryotes)
chemoheterotrophy (prokaryotes, protists, fungi,
animals, and some parasitic plants)
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C. The Role of Oxygen in Metabolism
 Prokaryotic metabolism varies with respect to O2:
– Obligate aerobes require O2 for cellular respiration
– Obligate anaerobes are poisoned by O2 and use
fermentation or anaerobic respiration
– Facultative anaerobes can survive with or without O2
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D. Nitrogen Metabolism
• Prokaryotes can metabolize nitrogen in a variety of ways
• In nitrogen fixation, some prokaryotes convert
atmospheric nitrogen (N2) to ammonia (NH3)
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E. Metabolic Cooperation
• Cooperation between prokaryotes allows them to use
environmental resources they could not use as
individual cells
• In the cyanobacterium Anabaena, photosynthetic cells
and nitrogen-fixing cells called heterocytes exchange
metabolic products
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Anabaena
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IV. Concept 27.4: Molecular Systematics
of Prokaryotic Phylogeny
• Molecular systematics (especially ribosomal RNA
comparison) has shown that prokaryotes diverged into
archaea and bacteria lineages very early in prokaryotic
evolution.
• Genetic diversity of prokaryotes is immense.
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A. Archaea
1. Archaea share certain traits with bacteria and other traits
2.
3.
4.
5.
with eukaryotes
Some archaea live in extreme environments and are called
extremophiles
Extreme halophiles live in highly saline environments
Extreme thermophiles thrive in very hot environments
Methanogens live in swamps and marshes and produce
methane as a waste product
•Methanogens are strict anaerobes and are poisoned by
O2
•Decomposers
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6. In recent years, genetic prospecting has revealed many
new groups of archaea
7. Some of these may offer clues to the early evolution of
life on Earth
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B. Bacteria
1. Bacteria include the vast majority of prokaryotes of which
most people are aware
2. Diverse nutritional types are scattered among the major
groups of bacteria (based mainly on comparisons of rRNA)
a. Proteobacteria—Largest and most diverse
b. Chlamydias—Parasites of animals
--Causes most common form of sexually transmitted
disease in U. S.
c. Spirochetes—Cause syphilis (Treponema pallidium)
--Cause Lyme Disease
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d. Gram-positive Bacteria
e. Cyanobacteria—photoautotrophs with plant-like
characteristics
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V. Concept 27.5: Roles in the
Biosphere
A. Chemical Cycles
1. Prokaryotes play a major role in the recycling of
chemical elements between the living and nonliving
components of ecosystems
2. Chemoheterotrophic prokaryotes function as
decomposers, breaking down corpses, dead vegetation,
and waste products
3. Nitrogen-fixing prokaryotes add usable nitrogen to the
environment
4. Prokaryotes can sometimes increase or decrease the
availability key plant nutrients
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B. Ecological Interactions
1. Symbiosis is an ecological relationship in which two
2.
3.
4.
5.
6.
species live in close contact: a larger host and smaller
symbiont
Prokaryotes often form symbiotic relationships with larger
organisms
In mutualism, both symbiotic organisms benefit
In commensalism, one organism benefits while neither
harming nor helping the other in any significant way
In parasitism, an organism called a parasite harms but
does not kill its host
Parasites that cause disease are called pathogens
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VI. Concept 27.6: Impacts on Humans
1. Some prokaryotes are human pathogens, but others
have positive interactions with humans
2. Pathogenic prokaryotes typically cause disease by
releasing exotoxins or endotoxins
• Exotoxins cause disease even if the prokaryotes that
produce them are not present (very toxic--botulism)
• Endotoxins are released only when bacteria die and
their cell walls break down (food poisoning)
3. Many pathogenic bacteria are potential weapons of
bioterrorism
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B. Prokaryotes in Research and Technology
1. Experiments using prokaryotes have led to important
advances in DNA technology
2. Prokaryotes are the principal agents in bioremediation, the
use of organisms to remove pollutants from the
environment
3. Some other uses of prokaryotes:
•Recovery of metals from ores
•Synthesis of vitamins
•Production of antibiotics, hormones, and other products
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Gleocapsa
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Nostoc
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You should now be able to:
1. Distinguish between the cell walls of gram-positive and gram-
negative bacteria
2. State the function of the following features: capsule, fimbriae,
sex pilus, nucleoid, plasmid, and endospore
3. Explain how R plasmids confer antibiotic resistance on bacteria
4. Distinguish among the following sets of terms:
photoautotrophs, chemoautotrophs, photoheterotrophs, and
chemoheterotrophs; obligate aerobe, facultative anaerobe, and
obligate anaerobe; mutualism, commensalism, and parasitism;
exotoxins and endotoxins
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