chapter 17 bacteria and archaea dentist: ©bsip/phototake; biofilm: ©dennis kunkel microscopy,...

Chapter 17 Bacteria and Archaea

Dentist: ©BSIP/Phototake; Biofilm: ©Dennis Kunkel Microscopy, Inc./Phototake

Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.

What Are Prokaryotes?

Section 17.1

A prokaryote is a single-celled organism that lacks a nucleus and membrane-bounded organelles.

Figure 17.1Bacteria: ©Kwangshin Kim/Science Source; Archaea: ©Ralph Robinson/Visuals Unlimited


Bacteria and archaea are prokaryotes belonging to distinct domains.

Section 17.1 Figure 17.1Bacteria: ©Kwangshin Kim/Science Source; Archaea: ©Ralph Robinson/Visuals Unlimited


DNA sequences and chemical composition distinguish these domains.



The first cells were likely prokaryotic. They have thrived for billions of years.


Clicker Question #1

According to the evolutionary tree below, why might the term “prokaryote” be controversial among scientists?

A. Prokaryotes are extinct.B. Prokaryotes consist of a small portion of life’s diversity.C. Prokaryotes consist of distantly related domains.D. All of the above are true.

Flower: © Doug Sherman/Geofile/RF

17.1 Mastering Concepts

What are two domains that contain prokaryotes?


Comparing Bacteria and Archaea

Section 15.1 Figure 17.2Section 17.2

The nucleoid is the region where the DNA resides.


Figure 17.3Section 17.2

Plasmids are circles of DNA apart from the chromosome.



Ribosomes use mRNA to synthesize proteins.



A pilus is a hair-like projection made of protein. Pili enable cells to adhere to objects.



A flagellum rotates like a propeller, allowing prokaryotes to move.



Flagella are used for taxis, movement toward or away from a stimulus.



The glycocalyx functions include protection and attachment.



The glycocalyx is a layer of proteins or polysaccharides surrounding the cell wall.

The cell wall gives the cell its shape.



Bacteria have two types of cell walls. Gram positive cells have a thick peptidoglycan (a carbohydrate) layer.

Bacteria Cell Walls Are Multi-layered

Figure 17.5Section 17.2 Stained bacteria: ©Jack Bostrack/Visuals Unlimited

Staining cells distinguishes bacteria based on cell wall type.

The three most common shapes are coccus (spherical), bacillus (rod-shaped), and spirillum (spiral).

Coccus: © David M. Phillips/Visuals Unlimited; Bacillus: © SciMAT/Photo Researchers; Spirillum: © Ed Reschke/Peter Arnold/Photolibrary

A Cell Wall Determines Cell Shape


Endospores Keep Some Bacteria Alive

Section 15.1 Figure 17.7

Some bacteria form thick-walled endospores that survive harsh conditions. Clostridium botulinum, the cause of botulism, is one example.

Section 17.2 Clostridium: ©Michael Abbey/Science Source

Scientists Classify Prokaryotes Based on Metabolic Pathways

Section 15.1

Prokaryotes obtain carbon and energy in many ways.

Section 17.2

Scientists Classify Prokaryotes Based on Metabolic Pathways

Section 15.1

Oxygen requirements are also important in classification. Aerobic habitats house obligate aerobes and facultative anaerobes; anaerobic habitats are home to obligate and

facultative anaerobes.


DNA sequences, such as those that encode ribosomal RNA, are important for distinguishing archaea and bacteria.


Scientists Classify Prokaryotes Based on Molecular Data

Bacteria: ©Kwangshin Kim/Science Source; Archaea: ©Ralph Robinson/Visuals Unlimited

Clicker Question #2

Bacteria, archaea, and eukaryotes all have ribosomes, but ribosome structure slightly varies between these groups. What is the best explanation for this observation?

A. The common ancestor of these three domains had ribosomes; slight changes have accumulated since the lineages split.B. Ribosomes arose independently in all three groups.



Prokaryotes Transmit DNA Vertically and Horizontally

Vertical gene transfer Horizontal gene transfer

Section 17.2


Vertical gene transfer

Vertical gene transfer is also called binary fission. It is an asexual process that replicates DNA and distributes it to two cells.



Horizontal gene transfer

In horizontal gene transfer, a cell receives DNA from a cell that is not its ancestor. This occurs in three ways.



Horizontal gene transfer: Transformation



Horizontal gene transfer: Transduction



Horizontal gene transfer: Conjugation

Clicker Question #3

What type of horizontal gene transfer relies on direct contact between two bacteria?

A. TransductionB. TransformationC. ConjugationD. Binary fission



Distinguish between vertical and horizontal gene transfer.


The Diversity of Domain Bacteria


Proteobacteria (left image) form one phylum of bacteria; their metabolic pathways and habitats are diverse.

Section 17.3

Proteobacteria

Bacteria: ©Dr Gopal Murti/Science Source; Anabaena: ©John Walsh/Science Source


E. coli and Salmonella are types of proteobacteria.

Proteobacteria

Figure 17.10Section 17.3 Bacteria: ©Dr Gopal Murti/Science Source; Anabaena: ©John Walsh/Science Source


Cyanobacteria (right image) form another phylum of bacteria. These autotrophs were the first to release oxygen gas as a byproduct of photosynthesis.

Proteobacteria Cyanobacteria



Other phyla of bacteria include Spirochaetes, Firmicutes, actinobacteria, and Chlamydiae.

Proteobacteria Cyanobacteria


The Diversity of Domain ArchaeaDomain Archaea are often collectively called extremophiles, since this domain was first discovered in extreme habitats.

Figure 17.11Section 17.3 Archaea habitat: ©Ralph Eagle Jr./Science Source; Inset: ©Eye of Science/Science Source

Archaea often live in places that lack oxygen or that are extremely hot, salty, or acidic.

But some live in moderate environments.

The Diversity of Domain Archaea

Archaea are essential in geochemical cycles on land and in water.

Figure 17.11Section 17.3 Archaea habitat: ©Ralph Eagle Jr./Science Source; Inset: ©Eye of Science/Science Source

Scientists are only beginning to organize Domain Archaea into phyla. •Euryarchaeota•Crenarchaeota•Korarchaeota

Clicker Question #4

Where (approximately) would you expect to find Salmonella on the evolutionary tree below?

AB C

D


Prokaryotes Are Essential to LifeProkaryotes in root nodules of some plants carry out nitrogen fixation, an essential process in which atmospheric nitrogen (N2) is converted to ammonia.

Figure 17.12Section 17.4 Rhizobium: ©Dr. John D. Cunningham/Visuals Unlimited; Root nodule cross section: ©Science VU/Visuals Unlimited

Only a few species of bacteria and archaea can use N2. Without nitrogen fixation, most nitrogen would be locked in the atmosphere.

Prokaryotes Are Essential to Life

Harmless bacteria in our bodies help crowd out pathogenic bacteria.



Section 17.4

Harmful bacteria might be ingested or inhaled, or they enter the body through wounds or orifices.

Salmonella is in undercooked eggs.

Raw egg: ©Ingram Publishing RF


Section 15.1

When we take antibiotics, some of our resident microbes die, sometimes leading to secondary infections.

Section 17.4 Pill: ©Rick Gomez/Corbis RF


Section 15.1

Prokaryotes also help make food and drugs. In wastewater treatment plants, microbes help break down organic matter.

Section 17.4 Figure 17.14Making cheese: ©Joe Munroe/Science Source; Humulin: ©David Wrobel/Visuals Unlimited ; Filter process: ©Jonathan A.Meyers/Science Source

Prokaryotes Are Everywhere

Section 15.1Section 17.4 Figure 17.17

This image shows a tiny sampling of the diversity of prokaryotes (bacteria, in this case) found at a park.

Clicker Question #5

Are the prokaryotes that typically reside inside of us useful?

A. No, we would be in better health without these microbes. B. Yes, they help crowd out harmful prokaryotes.


Clicker Question #5

Are the prokaryotes that typically reside inside of us useful?

A. No, we would be in better health without these microbes. B. Yes, they help crowd out harmful prokaryotes



In what ways are bacteria and archaea important to eukaryotic life in general and to human life in particular?



Investigating Life: A Bacterial Genome Solves

Two MysteriesScientists used bacterial DNA to determine the origins of antibiotic resistant bacteria (MRSA). Their results indicate that antibiotic resistance has evolved independently several times.



Two Mysteries

They also determined that bacteria that cause toxic shock syndrome have several separate origins.



Two Mysteries

Researching bacteria evolution helps to prevent the spread of disease.

chapter 17 bacteria and archaea dentist: ©bsip/phototake; biofilm: ©dennis kunkel microscopy,...

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