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? A prokaryote is a single-celled organism that lacks a nucleus and membrane-bounded organelles. Section 17.1 Figure 17.1 Bacteria: ©Kwangshin Kim/Science Source; Archaea: ©Ralph Robinson/Visuals Unlimited

What Are Prokaryotes? Bacteria and archaea are prokaryotes belonging to distinct domains. DNA sequences and chemical composition distinguish these domains. The first cells were likely prokaryotic. They have thrived for billions of years. Section 17.1 Figure 17.1 Bacteria: ©Kwangshin Kim/Science Source; Archaea: ©Ralph Robinson/Visuals Unlimited

Clicker Question #1 According to the evolutionary tree below, why might the term “prokaryote” be controversial among scientists? Prokaryotes are extinct. Prokaryotes consist of a small portion of life’s diversity. Prokaryotes consist of distantly related domains. All of the above are true. Flower: © Doug Sherman/Geofile/RF

Clicker Question #1 According to the evolutionary tree below, why might the term “prokaryote” be controversial among scientists? Prokaryotes are extinct. Prokaryotes consist of a small portion of life’s diversity. Prokaryotes consist of distantly related domains. All of the above are true. Flower: © Doug Sherman/Geofile/RF

Comparing Bacteria and Archaea Section 17.2 Section 15.1 Figure 17.2

Comparing Bacteria and Archaea The nucleoid is the region where the DNA resides. Section 17.2 Figure 17.3

Comparing Bacteria and Archaea Plasmids are circles of DNA apart from the chromosome. Section 17.2 Figure 17.3

Comparing Bacteria and Archaea Ribosomes use mRNA to synthesize proteins. Section 17.2 Figure 17.3

Comparing Bacteria and Archaea A pilus is a hair-like projection made of protein. Pili enable cells to adhere to objects. Section 17.2 Figure 17.3

Comparing Bacteria and Archaea A flagellum rotates like a propeller, allowing prokaryotes to move. Section 17.2 Figure 17.3

Comparing Bacteria and Archaea Flagella are used for taxis, movement toward or away from a stimulus. Section 17.2 Figure 17.3

Comparing Bacteria and Archaea The glycocalyx is a layer of proteins or polysaccharides surrounding the cell wall. The glycocalyx functions include protection and attachment. Section 17.2 Figure 17.3

Comparing Bacteria and Archaea The cell wall gives the cell its shape. Section 17.2 Figure 17.3

Bacteria Cell Walls Are Multi-layered Bacteria have two types of cell walls. Gram positive cells have a thick peptidoglycan (a carbohydrate) layer. Staining cells distinguishes bacteria based on cell wall type. Section 17.2 Figure 17.5 Stained bacteria: ©Jack Bostrack/Visuals Unlimited

A Cell Wall Determines Cell Shape The three most common shapes are coccus (spherical), bacillus (rod-shaped), and spirillum (spiral). Section 17.2 Coccus: © David M. Phillips/Visuals Unlimited; Bacillus: © SciMAT/Photo Researchers; Spirillum: © Ed Reschke/Peter Arnold/Photolibrary Figure 17.4

Endospores Keep Some Bacteria Alive Some bacteria form thick-walled endospores that survive harsh conditions. Clostridium botulinum, the cause of botulism, is one example. Section 15.1 Section 17.2 Figure 17.7 Clostridium: ©Michael Abbey/Science Source

Scientists Classify Prokaryotes Based on Metabolic Pathways Prokaryotes obtain carbon and energy in many ways. Section 17.2 Section 15.1

Scientists Classify Prokaryotes Based on Metabolic Pathways Oxygen requirements are also important in classification. Aerobic habitats house obligate aerobes and facultative anaerobes; anaerobic habitats are home to obligate and facultative anaerobes. Section 15.1 Section 17.2 Figure 17.8

Scientists Classify Prokaryotes Based on Molecular Data DNA sequences, such as those that encode ribosomal RNA, are important for distinguishing archaea and bacteria. Section 17.2 Figure 17.1 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? The common ancestor of these three domains had ribosomes; slight changes have accumulated since the lineages split. Ribosomes arose independently in all three groups. Flower: © Doug Sherman/Geofile/RF

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? The common ancestor of these three domains had ribosomes; slight changes have accumulated since the lineages split. Ribosomes arose independently in all three groups. Flower: © Doug Sherman/Geofile/RF

Prokaryotes Transmit DNA Vertically and Horizontally 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. Section 17.2

Prokaryotes Transmit DNA Vertically and Horizontally Horizontal gene transfer In horizontal gene transfer, a cell receives DNA from a cell that is not its ancestor. This occurs in three ways. Section 17.2 Figure 17.9

Prokaryotes Transmit DNA Vertically and Horizontally Horizontal gene transfer: Transformation Section 17.2 Figure 17.9

Prokaryotes Transmit DNA Vertically and Horizontally Horizontal gene transfer: Transduction Section 17.2 Figure 17.9

Prokaryotes Transmit DNA Vertically and Horizontally Horizontal gene transfer: Conjugation Section 17.2 Figure 17.9

Clicker Question #3 What type of horizontal gene transfer relies on direct contact between two bacteria? Transduction Transformation Conjugation Binary fission Flower: © Doug Sherman/Geofile/RF

Clicker Question #3 What type of horizontal gene transfer relies on direct contact between two bacteria? Transduction Transformation Conjugation Binary fission Flower: © Doug Sherman/Geofile/RF

The Diversity of Domain Bacteria Proteobacteria (left image) form one phylum of bacteria; their metabolic pathways and habitats are diverse. E. coli and Salmonella are types of proteobacteria. Proteobacteria Cyanobacteria (right image) form another phylum of bacteria. These autotrophs were the first to release oxygen gas as a byproduct of photosynthesis. Other phyla of bacteria include Spirochaetes, Firmicutes, actinobacteria, and Chlamydiae. Section 17.3 Section 15.1 Figure 17.10 Bacteria: ©Dr Gopal Murti/Science Source; Anabaena: ©John Walsh/Science Source

The Diversity of Domain Archaea Domain Archaea are often collectively called extremophiles, since this domain was first discovered in extreme habitats. Archaea often live in places that lack oxygen or that are extremely hot, salty, or acidic. But some live in moderate environments. Section 17.3 Figure 17.11 Archaea habitat: ©Ralph Eagle Jr./Science Source; Inset: ©Eye of Science/Science Source

The Diversity of Domain Archaea Archaea are essential in geochemical cycles on land and in water. Scientists are only beginning to organize Domain Archaea into phyla. Euryarchaeota Crenarchaeota Korarchaeota Section 17.3 Figure 17.11 Archaea habitat: ©Ralph Eagle Jr./Science Source; Inset: ©Eye of Science/Science Source

Clicker Question #4 Where (approximately) would you expect to find Salmonella on the evolutionary tree below? D B C A Flower: © Doug Sherman/Geofile/RF

Clicker Question #4 Where (approximately) would you expect to find Salmonella on the evolutionary tree below? D B C A Flower: © Doug Sherman/Geofile/RF

Prokaryotes Are Essential to Life Prokaryotes in root nodules of some plants carry out nitrogen fixation, an essential process in which atmospheric nitrogen (N2) is converted to ammonia. Only a few species of bacteria and archaea can use N2. Without nitrogen fixation, most nitrogen would be locked in the atmosphere. Section 17.4 Figure 17.12 Rhizobium: ©Dr. John D. Cunningham/Visuals Unlimited; Root nodule cross section: ©Science VU/Visuals Unlimited

Prokaryotes Are Essential to Life Harmless bacteria in our bodies help crowd out pathogenic bacteria. Section 17.4 Figure 17.13

Prokaryotes Are Essential to Life Salmonella is in undercooked eggs. Harmful bacteria might be ingested or inhaled, or they enter the body through wounds or orifices. Section 17.4 Raw egg: ©Ingram Publishing RF

Prokaryotes Are Essential to Life When we take antibiotics, some of our resident microbes die, sometimes leading to secondary infections. Section 15.1 Section 17.4 Pill: ©Rick Gomez/Corbis RF

Prokaryotes Are Essential to Life Prokaryotes also help make food and drugs. In wastewater treatment plants, microbes help break down organic matter. Section 15.1 Section 17.4 Making cheese: ©Joe Munroe/Science Source; Humulin: ©David Wrobel/Visuals Unlimited ; Filter process: ©Jonathan A. Meyers/Science Source Figure 17.14

Prokaryotes Are Everywhere This image shows a tiny sampling of the diversity of prokaryotes (bacteria, in this case) found at a park. Section 17.4 Section 15.1 Figure 17.17

Clicker Question #5 Are the prokaryotes that typically reside inside of us useful? No, we would be in better health without these microbes. Yes, they help crowd out harmful prokaryotes. Flower: © Doug Sherman/Geofile/RF

Clicker Question #5 Are the prokaryotes that typically reside inside of us useful? No, we would be in better health without these microbes. Yes, they help crowd out harmful prokaryotes Flower: © Doug Sherman/Geofile/RF