Michael Madigan • John Martinko
Brock Biology of
Microorganisms
Eleventh Edition
Chapter 2:
An Overview of Microbial Life
Copyright © 2006 Pearson Prentice Hall, Inc.

Chapter 2
I CELL STRUCTURE AND EVOLUTIONARY
HISTORY
2.1 Elements of Cell and Viral Structure
Eukaryotic Cells
Prokaryotic Cells
Viruses
2.2 Arrangement of DNA in Microbial Cells
Nucleus vs. Nucleoid
Genes, Genomes, and Proteins
2.3 The Tree of Life
The Three Domains of Life
Eukarya
Contributions of Molecular Sequencing to Microbiology

II MICROBIAL DIVERSITY
2.4 Physiological Diversity of Microorganisms
Chemoorganotrophs
Chemolithotrophs
Phototrophs
Heterotrophs and Autotrophs
Habitats and Extreme Environments
2.5 Prokaryotic Diversity
Bacteria
Archaea
Phylogenetic Analyses of Natural Microbial Communities
2.6 Eukaryotic Microorganisms
Eukaryotic Microbial Diversity
Final Remarks

An Overview of Microbial Life

I
CELL STRUCTURE AND
EVOLUTIONARY HISTORY

2.1 Elements of Cell and Viral Structure

Eukaryotic Cells

Prokaryotic Cells

Viruses

2.1 Concept Check
All microbial cells share certain basic structures in common such as a cytoplasmic membrane, ribosomes, and (usually) a cell wall. Two structural types of cells are recognized: the prokaryote and the eukaryote. Viruses are not cells but depend on cells for their replication.
• By looking inside a cell how could you tell if it was prokaryotic or eukaryotic ?
• What important function do ribosomes play in cells?
• How long is a typical rod-shaped bacterial cell? How much larger are you than this single cell?

2.2 Arrangement of DNA in
Microbial Cells

Nucleus vs. Nucleoid

Genes, Genomes, and Proteins

2.2 Concept Check
Genes govern the properties of cells, and a cell’s complement of genes is called its genome. DNA is arranged in cells to form chromosomes. In prokaryotes there is usually a single circular chromosome, while in eukaryotes, several linear chromosomes exist.
• Differentiate between the nucleus and the nucleoid .
• How do plasmids differ from chromosomes ?
• Why does it make sense that a human cell would have more genes than a bacterial cell?

2.3 The Tree of Life

The Three Domains of Life

Eukarya

Contributions of Molecular
Sequencing to Microbiology

2.3 Concept Check
Comparative ribosomal RNA sequencing has defined the three domains of life: Bacteria , Archaea , and Eukarya . Molecular sequencing has also shown that the major organelles of Eukarya have evolutionary roots in the Bacteria and has yielded new tools for microbial ecology and clinical microbiology.
• How can Bacteria and Archaea be differentiated? In what ways are they similar?
• What molecular evidence supports the theory of endosymbiosis?

II
MICROBIAL DIVERSITY

2.4 Physiological Diversity of
Microorganisms

Chemoorganotrophs

Chemolithotrophs

Phototrophs

Heterotrophs and Autotrophs

Habitats and Extreme
Environments

2.4 Concept Check
Carbon and energy sources are needed by all cells. The terms chemoorganotroph, chemolithotroph, and phototroph refer to cells that use organic chemicals, inorganic chemicals, or light, respectively, as their source of energy. Autotrophic organisms use
CO
2 as their carbon source, while heterotrophs use organic carbon.
Extremophiles thrive under environmental conditions that higher organisms cannot.
• How might you distinguish a phototrophic microorganism from a chemotrophic one by simply looking at it under a microscope?
• What are extremophiles ?

2.5 Prokaryotic Diversity

Bacteria

Archaea

Phylogenetic Analyses of Natural
Microbial Communities

2.5 Concept Check
Several lineages are present in the domains Bacteria and Archaea , and an enormous diversity of cell morphologies and physiologies are represented there. Retrieval and analysis of ribosomal RNA genes from cells in natural samples have shown that many phylogenetically distinct but as yet uncultured prokaryotes exist in nature.
• What important bacterial species that resides in your gut is a member of the Proteobacteria?
• Why can it be said that the cyanobacteria prepared Earth for the evolution of higher life forms?
• What is unusual about the genus Halobacterium ?
• How do we know a particular lineage of prokaryote exists in a natural habitat without first isolating and growing it in laboratory culture?

2.6 Eukaryotic Microorganisms

Eukaryotic Microbial Diversity

Final Remarks

2.6 Concept Check
Microbial eukaryotes are a diverse group that includes algae, protozoa, fungi, and slime molds. Some algae and fungi have developed mutualistic associations called lichens .
• List at least two ways algae differ from cyanobacteria.
• List at least two ways algae differ from protozoa.
• How do the components of a lichen benefit each other?