CHAPTER 27 Bacteria and Archaea

YOU MUST KNOW The key ways in which prokaryotes differ from eukaryotes with respect to:  Genome;  Membrane bound organelles;  Size;  Reproduction Mechanisms that contribute to genetic diversity in prokaryotes, including:  Transformation;  Conjugation;  Transduction;  Mutation

Structural & Functional Adaptations Structural and functional adaptations contribute to prokaryotic success:  Both the domain Bacteria and the domain Archaea are made up of prokaryotes.  Prokaryotes have NO TRUE NUCLEI or internal compartmentalization.  The DNA of prokaryotes is concentrated in the nucleoid region and has little associated protein.  Relative to eukaryotes, prokaryotes have simple, small genomes.  In addition to their one major chromosome, prokaryotic cells may also possess smaller, circular, independent pieces of DNA called plasmids.

Prokaryotic Shapes In general, prokaryotes exist in three common shapes:  Cocci (round)  Bacillus (rod-shaped)  Spirilla (spiral)

Prokaryotic Reproduction Prokaryotes reproduce through an asexual process called binary fission, and they continually synthesize DNA.

Prokaryotic Structure Outside their cell membranes, most prokaryotes possess a cell wall that contains peptidoglycan.  Gram-positive bacteria have simpler cell walls with more peptidoglycan.  Gram-negative bacteria have cell walls that are structurally more complex.

Prokaryotic Structure The cell wall of many prokaryotes is covered by a capsule, a sticky layer of polysaccharide or protein.  The capsule enables prokaryotes to adhere to other substrate or to other individuals in a colony. Some capsules protect against dehydration. Some prokaryotes stick to their substrate or to one another by means of hair-like appendages called fimbriae. The ability of some prokaryotes to withstand harsh conditions is attributed to endospores, a tough wall that forms outside the cell wall.

Prokaryotic Motility Prokaryotes use appendages called pili that adhere to each other or to surrounding surfaces. About half of the prokaryotes are motile, because they possess whiplike flagella.

Genetic Diversity in Prokaryotes Rapid reproduction, mutation, and genetic recombination promote genetic diversity in prokaryotes:  While mutation is the major source of genetic variation in prokaryotes, there are three mechanisms by which bacteria can transfer genetic material between each other: 1. Transformation (the uptake of foreign DNA from the surrounding environment). 2. Conjugation (the direct transfer of genes from one prokaryote to another). 3. Transduction (the transfer of genes from one prokaryote to another via a viral vector).

Lateral Gene Transfer in Prokaryotes

Major Nutritional Modes in Prokaryotes

Oxygen Needs in Prokaryotes Obligate aerobes cannot growth without oxygen because they need oxygen for cellular respiration. Obligate anaerobes are poisoned by oxygen. Some use fermentation, whereas others extract chemical energy by another form of anaerobic respiration. Facultative anaerobes use oxygen if it is available, when oxygen is not available, they undergo fermentation. Some prokaryotes can use atmospheric nitrogen as a direct source of nitrogen in a process called nitrogen fixation. They convert N 2 to NH 4 +.

Molecular Systematics & Prokaryotic Phylogeny Molecular systematics is illuminating prokaryotic phylogeny. The first prokaryotes that were classified in the domain Archaea are known as extremophiles and live in extreme environments:  Extreme Halophiles: live in saline environments.  Extreme Thermophiles: live in very hot environments. Other Archaea do not live in extreme environments.  Methanogens use carbon dioxide to oxidize H 2 and produce methane as a waste product.

Ecological Importance of Prokaryotes Prokaryotes play crucial roles in the biosphere:  Many prokaryotes are decomposers, breaking down dead organic matter.  Many prokaryotes are symbiotic, forming crucial relationships with other species.  Some prokaryotes are pathogenic and cause illness by producing poisons. Antibiotics are chemicals that can kill prokaryotes. They are NOT effective against viruses.  Many bacterial plasmids contain resistance genes to different antibiotics.

Human Uses of Prokaryotes Prokaryotes are used by humans in many ways:  Prokaryotes are used in bioremediation, removing pollutants from soil, air, or water.  Includes sewage treatment, oil spill clean up, and radioactive material precipitation.  Prokaryotes are symbionts in the gut, and can be used to make vitamins, and assist in digesting food.  Prokaryotes are used in gene cloning and producing transgenic organisms.  Prokaryotes are used in a wide variety of food productions: cheese, yogurt, and other products.