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Home , Archaea, Bacteria, Fission (biology)

Chapter 27 • thrive almost everywhere, including places too acidic, salty, cold, or hot for most and other • Most prokaryotes are microscopic, but what they lack in size they make up for in numbers • There are more in a handful of fertile than the number of people who have ever lived • Prokaryotes are divided into two domains: bacteria and archaea

Figure 27.2 Concept 27.1: Structural and functional adaptations contribute to prokaryotic success

• ’s first organisms were likely prokaryotes • Most prokaryotes are unicellular, although some form colonies • Most prokaryotic cells are 0.5–5 µm, much smaller than the 10–100 µm of many eukaryotic m cells m m 1 1 • Prokaryotic cells have a variety of shapes 3

• The three most common shapes are spheres (a) Spherical (b) Rod-shaped (c) Spiral (cocci), rods (), and spirals

Figure 27.UN03 Structure

Fimbriae -Surface Structures • An important feature of nearly all prokaryotic

Circular cells is their cell wall, which maintains cell shape, protects the cell, and prevents it from bursting in Capsule a hypotonic environment • Bacterial cell walls contain , a Sex network of sugar polymers cross-linked by

Internal organization polypeptides • Archaea contain and but lack peptidoglycan Flagella • Scientists use the to classify bacteria by cell wall composition • Gram-positive bacteria have simpler walls with a large amount of peptidoglycan • Gram-negative bacteria have less peptidoglycan and an outer membrane that can be toxic • Many target peptidoglycan and damage bacterial cell walls • Gram-negative bacteria are more likely to be resistant

• A or layer called a • Some prokaryotes have fimbriae , which allow capsule covers many prokaryotes them to stick to their substrate or other individuals in a colony • Pili (or sex pili) are longer than fimbriae and allow prokaryotes to exchange DNA

Motility • Flagella of bacteria, archaea, and are composed of different proteins and likely • In a heterogeneous environment, many bacteria evolved independently exhibit , the ability to move toward or away from a • is the movement toward or away from a chemical stimulus • Most motile bacteria propel themselves by flagella scattered about the surface or concentrated at one or both ends Figure 27.6 Internal Organization and DNA • The prokaryotic has less DNA than the • Prokaryotic cells usually lack complex eukaryotic genome compartmentalization • Some prokaryotes do have specialized • Most of the genome membranes that perform metabolic functions consists of a circular • These are usually infoldings of the plasma chromosome membrane • The chromosome is not surrounded by a membrane; it is located in the region

Figure 27.7 • Some species of bacteria also have smaller rings of Figure 27.8 DNA called

Reproduction and Adaptation

• There are some differences between prokaryotes • Prokaryotes reproduce quickly by binary and eukaryotes in DNA replication, , and can divide every 1–3 hours and • Key features of prokaryotic : • These allow people to use some antibiotics to – They are small inhibit without harming – They reproduce by binary fission themselves – They have short generation

• Many prokaryotes form metabolically inactive • Their short generation allows prokaryotes , which can remain viable in harsh to evolve quickly conditions for centuries – For example, adaptive in a bacterial colony was documented in a lab over 8 years • Prokaryotes are not “primitive” but are highly evolved Concept 27.2: Rapid reproduction, Rapid Reproduction and mutation, and • Prokaryotes reproduce by binary fission, and promote genetic diversity in prokaryotes offspring cells are generally identical • Prokaryotes have considerable genetic variation • Mutation rates during binary fission are low, but because of rapid reproduction, can • Three factors contribute to this genetic diversity: accumulate rapidly in a population – Rapid reproduction • High diversity from mutations allows for rapid – Mutation evolution – Genetic recombination

Genetic Recombination Transformation and

• Genetic recombination, the combining of DNA • A prokaryotic cell can take up and incorporate from two sources, contributes to diversity foreign DNA from the surrounding environment in • Prokaryotic DNA from different individuals can a process called transformation be brought together by transformation, • Transduction is the movement of transduction, and conjugation between bacteria by ( that • Movement of genes among individuals from infect bacteria) different species is called horizontal transfer

Figure 27.11-1 Figure 27.11-2 Phage Phage

A+++ B+++ A+++ B+++ Donor cell Donor cell

A+++ B+++ A+++ B+++

A+++ Figure 27.11-3 Figure 27.11-4 Phage Phage

A+++ B+++ A+++ B+++ Donor cell Donor cell

A+++ B+++ A+++ B+++

A+++ A+++

Recombination Recombination A+++ A+++

A−−− B−−− Recipient A−−− B−−− Recipient cell cell

A+++ B−−− Recombinant cell

Conjugation and Plasmids • Conjugation is the process where genetic The F Factor as a material is transferred between prokaryotic cells • In bacteria, the DNA transfer is one way • Cells containing the F plasmid function as DNA donors during conjugation • A donor cell attaches to a recipient by a pilus, pulls it closer, and transfers DNA • Cells without the F factor function as DNA recipients during conjugation • A piece of DNA called the F factor is required for the production of pili • The F factor is transferable during conjugation

Figure 27.12

Figure 27.13a-3

The F Factor in the Chromosome Bacterial F plasmid chromosome F+++ cell • A cell with the F factor built into its F+++ cell functions as a donor during conjugation (donor) • The recipient becomes a recombinant bacterium, bridge F−−− cell with DNA from two different cells (recipient) +++ Bacterial F cell chromosome

(a) Conjugation and transfer of an F plasmid Figure 27.13b-3

R Plasmids and Antibiotic Resistance • R plasmids carry genes for antibiotic resistance

Hfr cell A+++ A+++ • Antibiotics kill sensitive bacteria, but not bacteria (donor) A+++ −−− +++ F factor A+++ A A with specific R plasmids

−−− −−− −−− +++ −−− Recombinant F cell A A A A −−− • Through natural selection, the fraction of (recipient) F bacterium (b) Conjugation and transfer of part of an Hfr bacterial chromosome bacteria with genes for resistance increases in a population exposed to antibiotics • Antibiotic-resistant strains of bacteria are becoming more common

Concept 27.3: Diverse nutritional and The Role of in metabolic adaptations have evolved in prokaryotes • Prokaryotic metabolism varies with respect to O 2

– Obligate aerobes require O 2 for

– Obligate anaerobes are poisoned by O 2 and use or – Facultative anaerobes can survive with or

without O 2

Nitrogen Metabolism Metabolic Cooperation • Cooperation between prokaryotes allows them • is essential for the production of amino to use environmental resources they could not and nucleic acids use as individual cells • Prokaryotes can metabolize nitrogen in a variety • In the cyanobacterium , of ways photosynthetic cells and nitrogen-fixing cells • In nitrogen , some prokaryotes convert called heterocysts (or heterocytes) exchange atmospheric nitrogen (N 2) to (NH 3) metabolic products

Figure 27.14 Concept 27.4: Molecular is illuminating prokaryotic phylogeny • In some prokaryotic species, metabolic cooperation occurs in surface-coating colonies • Until the late 20th century, systematists based called prokaryotic on phenotypic criteria • Applying molecular systematics to the investigation of prokaryotic phylogeny has produced dramatic results

Figure 27.14

Lessons from Molecular Systematics • The use of chain reaction (PCR) has allowed for more rapid of • A handful of soil may contain 10,000 prokaryotic species • between prokaryotes obscures the of the tree of

Table 27.2 Archaea

• Archaea share certain traits with bacteria and other traits with eukaryotes • Some archaea live in extreme environments and • live in swamps and and are called produce as a waste product • Extreme live in highly saline • Methanogens are strict anaerobes and are

environments poisoned by O 2 • Extreme thrive in very hot • In recent years, genetic prospecting has environments revealed many new groups of archaea

Clades Bacteria

• Euryarcheota: many extreme halophiles, • Bacteria include the vast majority of prokaryotes of which most people are aware all known methanogens and some • Diverse nutritional types are scattered among the thermophiles major groups of bacteria • Crenarcheota: most of thermophiles – • : primitive thermophilic – organisms that do not belong to either – Spirochetes two above – – Gram-Positive Bacteria • : nanosized hyperthermophilic symbiont

Proteobacteria

• These gram-negative bacteria include • Many species are photoautotrophs, chemoautotrophs, and closely associated with eukaryotic hosts • Some are anaerobic, and others aerobic • Scientists hypothesize • Include subgroups: alpha, beta, gamma, delta that mitochondria and epsilon evolved from aerobic alpha proteobacteria through endosymbiosis • Examples include bacteria such as • Example: the soil and bacterium such as , which , , + converts NH 4 to and cholerae NO – 2 • coli resides in the intestines of many and is not normally pathogenic

• Example: the slime- • This group contains secreting many pathogens including , which causes poisoning, and pylori , which causes ulcers

Chlamydias Spirochetes • These bacteria are • These bacteria are helical heterotrophs parasites that live • Some are parasites, including within cells pallidum , which causes , and • burgdorferi , which causes Lyme trachomatis causes blindness and nongonococcal by sexual

Borrelia burgdorferi, Cyanobacteria Gram-Positive Bacteria • Actinomycetes, which decompose soil • These are photoautotrophs that generate O 2 • anthracis , the cause of • likely evolved from • botulinum , the cause of botulism cyanobacteria by the process of endosymbiosis • Some and , which can be pathogenic • Mycoplasms, the smallest known cells

Gloeocapsa

Concept 27.5: Prokaryotes play crucial Chemical Recycling roles in the • Prokaryotes play a major role in the recycling of • Prokaryotes are so important that if they were to chemical elements between the living and disappear the prospects for any other life nonliving components of surviving would be dim • Chemoheterotrophic prokaryotes function as , breaking down dead organisms and waste products

Ecological Interactions

• is an ecological relationship in which • In , both symbiotic organisms benefit. two species live in close contact: a larger The bacteria receive nutrients from this flashlight and smaller symbiont fish. The fish uses the light generated by the • Prokaryotes often form symbiotic relationships to attract prey and with larger organisms signal potential mates • In , one benefits while neither harming nor helping the other in any significant way Concept 27.6: Prokaryotes have both beneficial and harmful impacts on humans • In , an organism called a parasite harms but does not kill its host • Some prokaryotes are human pathogens, but • Parasites that cause disease are called others have positive interactions with humans pathogens • The ecological communities of hydrothermal vents depend on chemoautotropic bacteria for

Mutualistic Bacteria

• Human intestines are home to about 500–1,000 • Prokaryotes cause about half of all human species of bacteria • Many of these are mutalists and break down • Pathogenic prokaryotes typically cause that is undigested by our intestines disease by releasing or endotoxins • Exotoxins are secreted and cause disease even if the prokaryotes that produce them are not present • Endotoxins are released only when bacteria die and their cell walls break down

Prokaryotes in Research and Technology

• Experiments using prokaryotes have led to • Prokaryotes are the principal agents in important advances in DNA technology , the use of organisms to – For example, E. coli is used in gene remove pollutants from the environment – For example, tumefaciens is • Bacteria can be engineered to produce used to produce transgenic , antibiotics, and hormones • Bacteria can now be used to make natural • Bacteria are also being engineered to produce plastics from waste