Bacteria and Archaea

Chapter 27

LECTURE PRESENTATIONS

For CAMPBELL BIOLOGY, NINTH EDITION

Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson

© 2011 Pearson Education, Inc.

Lectures by

Erin Barley

Kathleen Fitzpatrick

Overview: Masters of Adaptation

• Utah’s Great Salt Lake can reach a salt concentration of 32%
• Its pink color comes from living prokaryotes

• Prokaryotes thrive almost everywhere, including places too acidic, salty, cold, or hot for most other organisms
• Most prokaryotes are microscopic, but what they lack in size they make up for in numbers
• There are more in a handful of fertile soil than the number of people who have ever lived
• Prokaryotes are divided into two domains: bacteria and archaea

Structural and functional adaptations contribute to prokaryotic success

• Earth’s first organisms were likely prokaryotes
• Most prokaryotes are unicellular, although some species form colonies
• Most prokaryotic cells are 0.5–5 µm, much smaller than the 10–100 µm of many eukaryotic cells
• Prokaryotic cells have a variety of shapes
• The three most common shapes are spheres (cocci), rods (bacilli), and spirals

Figure 27.2

(a) Spherical

(b) Rod-shaped

(c) Spiral

1 μm

1 μm

3 μm

Cell-Surface Structures

• An important feature of nearly all prokaryotic cells is their cell wall, which maintains cell shape, protects the cell, and prevents it from bursting in a hypotonic environment
• Eukaryote cell walls are made of cellulose or chitin
• Bacterial cell walls contain peptidoglycan, a network of sugar polymers cross-linked by polypeptides

• Archaea contain polysaccharides and proteins but lack peptidoglycan
• Scientists use the Gram stain to classify bacteria by cell wall composition
• Gram-positive bacteria have simpler walls with a large amount of peptidoglycan
• Gram-negative bacteria have less peptidoglycan and an outer membrane that can be toxic

Figure 27.3

(a) Gram-positive bacteria: peptidoglycan traps crystal violet.

Gram-positive

bacteria

Peptido-

glycan

layer

Cell

wall

Plasma

membrane

10 μm

Gram-negative

bacteria

Outer

membrane

Peptido-

glycan

layer

Plasma membrane

Cell

wall

Carbohydrate portion

of lipopolysaccharide

(b) Gram-negative bacteria: crystal violet is easily rinsed

away, revealing red dye.

• Many antibiotics target peptidoglycan and damage bacterial cell walls
• Gram-negative bacteria are more likely to be antibiotic resistant
• A polysaccharide or protein layer called a capsule covers many prokaryotes

Figure 27.4

Bacterial

cell wall

Bacterial

capsule

Tonsil

cell

200 nm

• Some prokaryotes have fimbriae, which allow them to stick to their substrate or other individuals in a colony
• Pili (or sex pili) are longer than fimbriae and allow prokaryotes to exchange DNA

Figure 27.5

Fimbriae

1 μm

Motility

• In a heterogeneous environment, many bacteria exhibit taxis, the ability to move toward or away from a stimulus
• Chemotaxis is the movement toward or away from a chemical stimulus

• Most motile bacteria propel themselves by flagella scattered about the surface or concentrated at one or both ends
• Flagella of bacteria, archaea, and eukaryotes are composed of different proteins and likely evolved independently

Figure 27.6

Flagellum

Hook

Motor

Filament

Rod

Peptidoglycan

layer

Plasma

membrane

Cell wall

20 nm

Internal Organization and DNA

• Prokaryotic cells usually lack complex compartmentalization
• Some prokaryotes do have specialized membranes that perform metabolic functions
• These are usually infoldings of the plasma membrane

• The prokaryotic genome has less DNA than the eukaryotic genome
• Most of the genome consists of a circular chromosome
• The chromosome is not surrounded by a membrane; it is located in the nucleoid region
• Some species of bacteria also have smaller rings of DNA called plasmids

Figure 27.8

Chromosome

Plasmids

1 μm

• There are some differences between prokaryotes and eukaryotes in DNA replication, transcription, and translation
• These allow people to use some antibiotics to inhibit bacterial growth without harming themselves

Reproduction and Adaptation

• Prokaryotes reproduce quickly by binary fission and can divide every 1–3 hours
• Key features of prokaryotic reproduction:
• They are small
• They reproduce by binary fission
• They have short generation times

• Many prokaryotes form metabolically inactive endospores, which can remain viable in harsh conditions for centuries

Figure 27.9

Coat

Endospore

0.3 μm

• Their short generation time allows prokaryotes to evolve quickly
• For example, adaptive evolution in a bacterial colony was documented in a lab over 8 years
• Prokaryotes are not “primitive” but are highly evolved

Rapid reproduction, mutation, and genetic recombination promote genetic diversity in prokaryotes

• Prokaryotes have considerable genetic variation
• Three factors contribute to this genetic diversity:
• Rapid reproduction
• Mutation
• Genetic recombination

Rapid Reproduction and Mutation

• Prokaryotes reproduce by binary fission, and offspring cells are generally identical
• Mutation rates during binary fission are low, but because of rapid reproduction, mutations can accumulate rapidly in a population
• High diversity from mutations allows for rapid evolution

​

Genetic Recombination

• Genetic recombination, the combining of DNA from two sources, contributes to diversity
• Prokaryotic DNA from different individuals can be brought together by transformation, transduction, and conjugation
• Movement of genes among individuals from different species is called horizontal gene transfer

Transformation and Transduction

• A prokaryotic cell can take up and incorporate foreign DNA from the surrounding environment in a process called transformation
• Transduction is the movement of genes between bacteria by bacteriophages (viruses that infect bacteria)

Figure 27.11-1

Donor cell

A⁺

B⁺

B⁺

A⁺

Phage

Figure 27.11-2

A⁺

Donor cell

A⁺

B⁺

B⁺

A⁺

Phage

Figure 27.11-3

Recipient

cell

Recombination

A⁺

A⁺

A⁻

B⁻

Donor cell

A⁺

B⁺

B⁺

A⁺

Phage

Figure 27.11-4

Recombinant cell

Recipient

cell

Recombination

A⁺

A⁺

A⁻

B⁻

B⁻

A⁺

Donor cell

A⁺

B⁺

B⁺

A⁺

Phage

Conjugation and Plasmids

• Conjugation is the process where genetic material is transferred between prokaryotic cells
• In bacteria, the DNA transfer is one way
• A donor cell attaches to a recipient by a pilus, pulls it closer, and transfers DNA
• A piece of DNA called the F factor is required for the production of pili

Figure 27.12

Sex pilus

1 μm

The F Factor as a Plasmid

• Cells containing the F plasmid function as DNA donors during conjugation
• Cells without the F factor function as DNA recipients during conjugation
• The F factor is transferable during conjugation

Figure 27.13

F plasmid

Bacterial chromosome

F⁺ cell

(donor)

F⁻ cell

(recipient)

Mating

bridge

Bacterial

chromosome

(a) Conjugation and transfer of an F plasmid

Hfr cell

(donor)

F⁻ cell

(recipient)

(b) Conjugation and transfer of part of an Hfr bacterial chromosome

F factor

A⁺

A⁻

A⁺

A⁻

A⁺

A⁺

A⁻

F⁺ cell

F⁺ cell

A⁺

A⁻

Recombinant

F⁻ bacterium

A⁺

Figure 27.13a-1

F plasmid

Bacterial

chromosome

F⁺ cell

(donor)

F⁻ cell

(recipient)

Mating

bridge

Bacterial

chromosome

(a) Conjugation and transfer of an F plasmid

Figure 27.13a-2

F plasmid

Bacterial

chromosome

F⁺ cell

(donor)

F⁻ cell

(recipient)

Mating

bridge

Bacterial

chromosome

(a) Conjugation and transfer of an F plasmid

Figure 27.13a-3

F plasmid

Bacterial

chromosome

F⁺ cell

(donor)

F⁻ cell

(recipient)

Mating

bridge

Bacterial

chromosome

(a) Conjugation and transfer of an F plasmid

F⁺ cell

F⁺ cell

The F Factor in the Chromosome

• 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

Figure 27.13b-1

Hfr cell

(donor)

F⁻ cell

(recipient)

(b) Conjugation and transfer of part of an Hfr bacterial chromosome

F factor

A⁻

A⁺

A⁺

A⁻

A⁺

Figure 27.13b-2

Hfr cell

(donor)

F⁻ cell

(recipient)

(b) Conjugation and transfer of part of an Hfr bacterial chromosome

F factor

A⁺

A⁺

A⁻

A⁻

A⁺

A⁺

A⁻

A⁺

Figure 27.13b-3

Hfr cell

(donor)

F⁻ cell

(recipient)

(b) Conjugation and transfer of part of an Hfr bacterial chromosome

F factor

A⁺

A⁻

Recombinant

F⁻ bacterium

A⁺

A⁺

A⁻

A⁻

A⁺

A⁺

A⁻

A⁺

R Plasmids and Antibiotic Resistance

• R plasmids carry genes for antibiotic resistance
• Antibiotics kill sensitive bacteria, but not bacteria with specific R plasmids
• Through natural selection, the fraction of bacteria with genes for resistance increases in a population exposed to antibiotics
• Antibiotic-resistant strains of bacteria are becoming more common

Diverse nutritional and metabolic adaptations have evolved in prokaryotes

• Prokaryotes can be categorized by how they obtain energy and carbon
• Phototrophs obtain energy from light
• Chemotrophs obtain energy from chemicals
• Autotrophs require CO₂ as a carbon source
• Heterotrophs require an organic nutrient to make organic compounds

• Energy and carbon sources are combined to give four major modes of nutrition:
• Photoautotrophy
• Chemoautotrophy
• Photoheterotrophy
• Chemoheterotrophy

Table 27.1

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

Nitrogen Metabolism

• Nitrogen is essential for the production of amino acids and nucleic acids
• Prokaryotes can metabolize nitrogen in a variety of ways
• In nitrogen fixation, some prokaryotes convert atmospheric nitrogen (N₂) to ammonia (NH₃)

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 heterocysts (or heterocytes) exchange metabolic products

• In some prokaryotic species, metabolic cooperation occurs in surface-coating colonies called biofilms

Archaea

• Almost since their origin 3.5 billion years ago, prokaryotes have evolved in two separate lineages, the bacteria and archaea. The first prokaryotes that were classified in the domain Archaea are known as extremophiles and live in extreme environments.

Eukarya

Archaea

Bacteria

Table 27.2

• 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
• In recent years, genetic prospecting has revealed many new groups of archaea
• Some of these may offer clues to the early evolution of life on Earth

Prokaryotes play crucial roles in the biosphere

• Prokaryotes are so important that if they were to disappear the prospects for any other life surviving would be dim

Chemical Recycling

• Prokaryotes play a major role in the recycling of chemical elements between the living and nonliving components of ecosystems
• Chemoheterotrophic prokaryotes function as decomposers, breaking down dead organisms and waste products
• Prokaryotes can sometimes increase the availability of nitrogen, phosphorus, and potassium for plant growth

• Prokaryotes can also “immobilize” or decrease the availability of nutrients

Ecological Interactions

• Symbiosis is an ecological relationship in which two 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

​

Prokaryotes have both beneficial and harmful impacts on humans

• Some prokaryotes are human pathogens, but others have positive interactions with humans
• Mutualistic Bacteria
• Human intestines are home to about 500–1,000 species of bacteria
• Many of these are mutualists and break down food that is undigested by our intestines

​

Pathogenic Bacteria

• Prokaryotes cause about half of all human diseases
• For example, Lyme disease is caused by a bacterium and carried by ticks
• Prokaryotes are the principal agents in bioremediation, the use of organisms to remove pollutants from the environment
• Bacteria can be engineered to produce vitamins, antibiotics, and hormones
• Bacteria are also being engineered to produce ethanol from waste biomass

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