Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CHAPTER 27 Prokaryotes

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Prokaryotes thrive almost everywhere – Including places too acidic, too salty, too cold, or too hot for most other organisms Figure 27.1

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Structural, functional, and genetic adaptations contribute to prokaryotic success Most prokaryotes are unicellular – Although some species form colonies

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Prokaryotic cells have a variety of shapes – The three most common of which are spheres (cocci), rods (bacilli), and spirals 1  m 2  m 5  m (a) Spherical (cocci) (b) Rod-shaped (bacilli) (c) Spiral Figure 27.2a–c

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Using a technique called the Gram stain – Scientists can classify many bacterial species into two groups based on cell wall composition, Gram- positive and Gram-negative (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. (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. Figure 27.3a, b Peptidoglycan layer Cell wall Plasma membrane Protein Gram- positive bacteria 20  m Outer membrane Peptidoglycan layer Plasma membrane Cell wall Lipopolysaccharide Protein Gram- negative bacteria

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The cell wall of many prokaryotes – Is covered by a capsule, a sticky layer of polysaccharide or protein Some prokaryotes have fimbriae and pili – Which allow them to stick to their substrate or other individuals in a colony Capsule Fimbriae

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Motility Most motile bacteria propel themselves by flagella – Which are structurally and functionally different from eukaryotic flagella Flagellum Filament Hook Cell wall Plasma membrane Basal apparatus 50 nm Figure 27.6

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The typical prokaryotic genome – Is a ring of DNA that is not surrounded by a membrane and that is located in a nucleoid region Figure  m Chromosome

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Prokaryotes reproduce quickly by binary fission – And can divide every 1–3 hours

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A great diversity of nutritional and metabolic adaptations have evolved in prokaryotes Types of nutrition: – Photoautotrophy: light + atmospheric CO2 = organic compounds (cyanobacteria, plants, algae, protists) – Chemoautotrophy: inorganic substances (ammonia, sulfide) + atmospheric CO2 = organic compounds. – Photoheterotrophy: light for energy and carbon in organic form (marine prokaryotes) – Chemoheterotrophy: consume organic compounds for both energy and carbon (decomposers)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Major nutritional modes in prokaryotes Table 27.1

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Prokaryotic metabolism – Obligate aerobes Require oxygen – Facultative anaerobes Can survive with or without oxygen – Obligate anaerobes Are poisoned by oxygen Metabolic Relationships to Oxygen

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Lessons from Molecular Systematics Molecular systematics – Is leading to a phylogenetic classification of prokaryotes – 2 clades of prokaryotes: bacteria and archaea Domain Bacteria Domain Archaea Domain Eukarya Alpha Beta Gamma Epsilon Delta Proteobacteria Chlamydias Spirochetes Cyanobacteria Gram-positive bacteria Korarchaeotes Euryarchaeotes Crenarchaeotes Nanoarchaeotes Eukaryotes Universal ancestor

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Bacteria Diverse nutritional types – Are scattered among the major groups of bacteria The two largest groups are – The proteobacteria and the Gram-positive bacteria

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Archaea Archaea share certain traits with bacteria Table And other traits with eukaryotes - Have many unique characteristics

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Archaea Live in extreme environments – Extreme thermophiles Thrive in very hot environments – Extreme halophiles Live in high saline environments – Methanogens Live in swamps and marshes Produce methane as a waste product

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Roles of prokaryotes 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chemoheterotrophic prokaryotes function as decomposers – Breaking down corpses, dead vegetation, and waste products – Recycling of chemical elements between the living and nonliving components of the environment in ecosystems Nitrogen-fixing prokaryotes – Add usable nitrogen to the environment

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Symbiotic Relationships Many prokaryotes – Live with other organisms in symbiotic relationships such as mutualism and commensalism Figure 27.15

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Other types of prokaryotes – Live inside hosts as parasites Prokaryotes have both harmful and beneficial impacts on humans Some prokaryotes are human pathogens – But many others have positive interactions with humans

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Pathogenic Prokaryotes Prokaryotes cause about half of all human diseases – Lyme disease is an example 5 µm Figure 27.16

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Prokaryotes in Research and Technology Experiments using prokaryotes – Have led to important advances in DNA technology Prokaryotes are also major tools in – Mining – The synthesis of vitamins – Production of antibiotics, hormones, and other products