27
Prokaryotes
PowerPoint Chapter Lectures for Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Overview: They're (Almost) Everywhere! Most prokaryotes are microscopic
But what they lack in size they more than make up for in numbers
The number of prokaryotes in a single handful of fertile soil
Is greater than the number of people who have ever lived
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Prokaryotes thrive almost everywhere
Including places too acidic, too salty, too cold, or too hot for most other organisms
Figure 27.1
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Biologists are discovering
That these organisms have an astonishing genetic diversity
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Concept 27.1: Structural, functional, and genetic adaptations contribute to prokaryotic success Most prokaryotes are unicellular
Although some species form colonies
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Prokaryotic cells have a variety of shapes
The three most common of which are spheres (cocci), rods (bacilli), and spirals
1 m Figure 27.2ac (a) Spherical (cocci)
2 m (b) Rod-shaped (bacilli)
(c) Spiral
5 m
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Cell-Surface Structures One of the most important features of nearly all prokaryotic cells
Is their cell wall, which maintains cell shape, provides physical protection, and prevents the cell from bursting in a hypotonic environment
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Using a technique called the Gram stain
Scientists can classify many bacterial species into two groups based on cell wall composition, Grampositive and Gram-negative
Lipopolysaccharide Peptidoglycan layer Plasma membrane Outer membrane Cell wall Cell wall Peptidoglycan layer Plasma membrane Protein Gramnegative bacteria 20 m
Protein Grampositive bacteria
(a) Gram-positive. Gram-positive bacteria have a cell wall with a large amount of peptidoglycan that traps the violet dye in the cytoplasm. The alcohol rinse does not remove the violet dye, which masks the added red dye. Figure 27.3a, b
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(b) Gram-negative. Gram-negative bacteria have less peptidoglycan, and it is located in a layer between the plasma membrane and an outer membrane. The violet dye is easily rinsed from the cytoplasm, and the cell appears pink or red after the red dye is added.
The cell wall of many prokaryotes
Is covered by a capsule, a sticky layer of polysaccharide or protein
200 nm
Capsule
Figure 27.4
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Some prokaryotes have fimbriae and pili
Which allow them to stick to their substrate or other individuals in a colony
Fimbriae 200 nm
Figure 27.5
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Motility
Most motile bacteria propel themselves by flagella Which are structurally and functionally different from eukaryotic flagella
Flagellum Filament 50 nm Cell wall Hook Basal apparatus
Figure 27.6
Plasma membrane
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In a heterogeneous environment, many bacteria exhibit taxis
The ability to move toward or away from certain stimuli
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Internal and Genomic Organization Prokaryotic cells
Usually lack complex compartmentalization
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Some prokaryotes
Do have specialized membranes that perform metabolic functions
0.2 m 1 m
Respiratory membrane
Thylakoid membranes Figure 27.7a, b (a) Aerobic prokaryote (b) Photosynthetic prokaryote
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The typical prokaryotic genome
Is a ring of DNA that is not surrounded by a membrane and that is located in a nucleoid region
Chromosome
Figure 27.8
1 m
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Some species of bacteria
Also have smaller rings of DNA called plasmids
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Reproduction and Adaptation Prokaryotes reproduce quickly by binary fission
And can divide every 13 hours
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Many prokaryotes form endospores
Which can remain viable in harsh conditions for centuries
Endospore
Figure 27.9
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0.3 m
Rapid reproduction and horizontal gene transfer
Facilitate the evolution of prokaryotes to changing environments
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Concept 27.2: A great diversity of nutritional and metabolic adaptations have evolved in prokaryotes Examples of all four models of nutrition are found among prokaryotes
Photoautotrophy Chemoautotrophy Photoheterotrophy Chemoheterotrophy
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Major nutritional modes in prokaryotes
Table 27.1
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Metabolic Relationships to Oxygen Prokaryotic metabolism
Also varies with respect to oxygen
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Obligate aerobes
Require oxygen
Facultative anaerobes
Can survive with or without oxygen
Obligate anaerobes
Are poisoned by oxygen
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Nitrogen Metabolism Prokaryotes can metabolize nitrogen
In a variety of ways
In a process called nitrogen fixation
Some prokaryotes convert atmospheric nitrogen ammonia
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Metabolic Cooperation Cooperation between prokaryotes
Allows them to use environmental resources they could not use as individual cells
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In the cyanobacterium Anabaena
Photosynthetic cells and nitrogen-fixing cells exchange metabolic products
Photosynthetic cells
Heterocyst
20 m
Figure 27.10
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In some prokaryotic species
Metabolic cooperation occurs in surfacecoating colonies called biofilms
Figure 27.11
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1 m
Concept 27.3: Molecular systematics is illuminating prokaryotic phylogeny Until the late 20th century
Systematists based prokaryotic taxonomy on phenotypic criteria
Applying molecular systematics to the investigation of prokaryotic phylogeny
Has produced dramatic results
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Lessons from Molecular Systematics Molecular systematics
Is leading to a phylogenetic classification of prokaryotes Is allowing systematists to identify major new clades
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A tentative phylogeny of some of the major taxa of prokaryotes based on molecular systematics
Domain Bacteria
Cyanobacteria Gram-positive bacteria Korarchaeotes
Domain Archaea
Crenarchaeotes Euryarchaeotes Nanoarchaeotes
Domain Eukarya
Proteobacteria
Chlamydias Spirochetes
Gamma
Alpha
Delta
Epsilon
Figure 27.12
Universal ancestor
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Eukaryotes
Beta
Bacteria Diverse nutritional types
Are scattered among the major groups of bacteria
The two largest groups are
The proteobacteria and the Gram-positive bacteria
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Proteobacteria
Rhizobium (arrows) inside a root cell of a legume (TEM)
2.5 m
Nitrosomonas (colorized TEM)
Chromatium; the small globules are sulfur wastes (LM)
10 m
0.5 m
1 m
Fruiting bodies of Chondromyces crocatus, a myxobacterium (SEM)
Bdellovibrio bacteriophorus Attacking a larger bacterium (colorized TEM)
Figure 27.13
Helicobacter pylori (colorized TEM).
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2 m
5 m
Chlamydias, spirochetes, Gram-positive bacteria, and cyanobacteria
Chlamydia (arrows) inside an animal cell (colorized TEM)
2.5 m
Leptospira, a spirochete (colorized TEM)
5 m
Hundreds of mycoplasmas Streptomyces, the source of covering a human fibroblast cell many antibiotics (colorized SEM) (colorized SEM)
Figure 27.13
Two species of Oscillatoria, filamentous cyanobacteria (LM)
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50 m
5 m
1 m
Archaea Archaea share certaintraits with bacteria
And other traits with eukaryotes
Table 27.2
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Some archaea
Live in extreme environments
Extreme thermophiles
Thrive in very hot environments
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Extreme halophiles
Live in high saline environments
Figure 27.14
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Methanogens
Live in swamps and marshes Produce methane as a waste product
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Concept 27.4: Prokaryotes play crucial roles in the biosphere Prokaryotes are so important to the biosphere that if they were to disappear
The prospects for any other life surviving would be dim
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Chemical Recycling Prokaryotes play a major role
In the continual recycling of chemical elements between the living and nonliving components of the environment in ecosystems
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Chemoheterotrophic prokaryotes function as decomposers
Breaking down corpses, dead vegetation, and waste products
Nitrogen-fixing prokaryotes
Add usable nitrogen to the environment
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Symbiotic Relationships Many prokaryotes
Live with other organisms in symbiotic relationships such as mutualism and commensalism
Figure 27.15
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Other types of prokaryotes
Live inside hosts as parasites
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Concept 27.5: Prokaryotes have both harmful and beneficial impacts on humans Some prokaryotes are human pathogens
But many others have positive interactions with humans
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Pathogenic Prokaryotes Prokaryotes cause about half of all human diseases
Lyme disease is an example
Figure 27.16
5 m
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Pathogenic prokaryotes typically cause disease
By releasing exotoxins or endotoxins
Many pathogenic bacteria
Are potential weapons of bioterrorism
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Prokaryotes in Research and Technology Experiments using prokaryotes
Have led to important advances in DNA technology
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Prokaryotes are the principal agents in bioremediation
The use of organisms to remove pollutants from the environment
Figure 27.17
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Prokaryotes are also major tools in
Mining The synthesis of vitamins Production of antibiotics, hormones, and other products
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