Biology, Prokaryotes CH27

RAVEN Biology 13th edition, CH27

History of Microbiology 1, The size of prokaryotic cells led to their being undiscovered for most of human history

Undiscovered for most of human history

History of Microbiology 1, In 1546, Italian physician Girolamo Fracastoro suggested that disease was caused by unseen organisms

Caused by unseen organisms

History of Microbiology 1, Two lines of technology

Microscopy for visualization and Infectious disease investigations

History of Microbiology 2, Antony van Leeuwenhoek was first to observe and accurately describe microbial life

First to observe and describe microbial life

History of Microbiology 2, Modern electron microscopes allows

study of cell substructure

History of Microbiology 2, Louis Pasteur refutes idea of spontaneous generation

Idea that living things arise spontaneously from other living things

History of Microbiology 3, Robert Koch studied anthrax; proposed four postulates to prove a causal relationship between a microorganism and a disease

Proposed four postulates

History of Microbiology 3, Koch's Postulate 1

The microorganism must be present in every case of the disease and absent from healthy individuals

History of Microbiology 3, Koch's Postulate 2

The putative causative agent must be isolated and grown in pure culture

History of Microbiology 3, Koch's Postulate 3

The same disease must result when the cultured microorganism is used to infect a healthy host

History of Microbiology 3, Koch's Postulate 4

The same microorganism must be isolated again from the diseased host

Prokaryotic Diversity, Oldest, structurally simplest, and most abundant forms of life

Oldest, simplest, most abundant

Prokaryotic Diversity, Abundant for over

a billion years before eukaryotes appeared

Prokaryotic Diversity, 90-99%

unknown and undescribed

Prokaryotic Diversity, Fall into 2 domains

Bacteria and Archaea

Prokaryotic Diversity, Many archaea are extremophiles

Extremophiles

Characteristics of Prokaryotes 1, Unicellularity

Most are single-celled; May stick together to form associations and biofilms

Characteristics of Prokaryotes 1, Cell size

Size varies tremendously; Most are less than 1 μm in diameter

Characteristics of Prokaryotes 1, Nucleoid

Chromosome is single circular double-stranded DNA; Found in the nucleoid region of cell; Often have plasmids

Characteristics of Prokaryotes 1, Cell division and genetic recombination

Most divide by binary fission; Exchange genes through horizontal gene transfer; not a form of reproduction

Characteristics of Prokaryotes 2, Internal compartmentalization

No membrane-bounded organelles; No internal compartment; Plasma membrane can be extensively inflated

Characteristics of Prokaryotes 2, Flagella

Simple in structure; Different from eukaryotic flagella

Characteristics of Prokaryotes 2, Pili

Protein filaments extending from the surface

Characteristics of Prokaryotes 2, Metabolic diversity

Oxygenic and anoxygenic photosynthesis; Chemolithotrophic

Bacteria versus Archaea 1, 1. Plasma membranes

All prokaryotes have a plasma membrane

Bacteria versus Archaea 1, Membranes of archaea

differ from bacteria and eukaryotes

Bacteria versus Archaea 1, Archaean membranes are formed of glycerol linked to hydrocarbon chains by

Ether linkages (not ester like bacteria & eukaryotes)

Bacteria versus Archaea 1, Hydrocarbons may be branched

May be branched

Bacteria versus Archaea 1, Tetraethers form a monolayer instead of a bilayer

Allows extremophiles to withstand high temperatures

Bacteria versus Archaea 2, Cell wall

All prokaryotes have cell walls; Bacteria have peptidoglycan; Archaea lack peptidoglycan

Bacteria versus Archaea 2, DNA replication

Both have single replication origin; nature of origin and proteins used are different; Archaeal DNA replication is more similar to that of eukaryotes

Bacteria versus Archaea 2, Gene Expression

Archaeal transcription and translation are more similar to those of eukaryotes

Early Classification Characteristics, Prokaryotes are not

easily classified according to forms

Early Classification Characteristics, Early systems relied on staining characteristics and observable phenotypes

Relied on staining and phenotypes

Early Classification Characteristics, Characteristics used included: Photosynthetic ability; Cell wall structure; Motility; Unicellular, colony-forming, or filamentous; Spore-forming ability; Importance as human pathogens or not

Used characteristics

Modern Molecular Classification, 1. Amino acid sequences of key proteins

Amino acid sequences

Modern Molecular Classification, 2. Percent guanine-cytosine content

GC content

Modern Molecular Classification, 3. Nucleic acid hybridization

Closely related species will have more base pairing

Modern Molecular Classification, 4. Gene and RNA sequencing

Especially rRNA

Modern Molecular Classification, 5. Whole-genome sequencing

Whole-genome sequencing

Modern Molecular Classification 2, Based on these molecular data, several prokaryotic groupings have been proposed

Groupings proposed

Modern Molecular Classification 2, Bergey's Manual of Systematic Bacteriology, 2nd edition

Bergey's Manual

Modern Molecular Classification 2, Large scale sequencing of random samples indicates vast majority of bacteria have never been cultured or studied in detail

Majority never cultured

Prokaryotic Shapes, 3 basic shapes

Bacillus, Coccus, Spirillum

Prokaryotic Shapes, Bacillus

Rod-shaped

Prokaryotic Shapes, Coccus

Spherical

Prokaryotic Shapes, Spirillum

Helical-shaped

Prokaryotic Cell Characteristics, Cell wall

Peptidoglycan forms a rigid network; Maintains shape; Withstands hypotonic environments

Prokaryotic Cell Characteristics, Archaea have a similar molecule (pseudomurein)

Similar molecule is pseudomurein

Prokaryotic Cell Characteristics, Gram stain

Gram-positive bacteria have a thicker peptidoglycan wall and stain a purple color; Gram-negative bacteria contain less peptidoglycan and do not retain the purple-colored dye – retain counterstain and look pink

Prokaryotic cell walls 1, Gram positive bacteria

Thick, complex network of peptidoglycan; Also contains lipoteichoic and teichoic acid

Prokaryotic cell walls 1, Gram negative bacteria

Thin layer of peptidoglycan; Second outer membrane with lipopolysaccharide; Resistant to many antibiotics

Prokaryotic cell walls 2, S-layer

Rigid paracrystalline layer found in some bacteria and archaea; Outside of peptidoglycan or outer membrane layers in gram-negative and gram-positive bacteria; Diverse functions – often involves adhesion

Prokaryotic cell walls 2, Capsule

Gelatinous layer found in some bacteria; Aids in attachment; Protects from the immune system

Bacterial flagella and pili, Flagella

Slender, rigid, helical structures; Composed of the protein flagellin; Involved in locomotion – spin like propeller

Bacterial flagella and pili, Pili

Short, hairlike structures; Found in gram-negative bacteria; Aid in attachment and conjugation

Endospores, Develop a thick wall around their genome and some of the cytoplasm when exposed to environmental stress

Develop thick wall under stress

Endospores, Highly resistant to environmental stress

Especially heat

Endospores, When conditions improve can germinate and return to normal cell division

Germinate when conditions improve

Endospores, Bacteria causing tetanus, botulism, and anthrax

Examples of endospore-formers

Prokaryotic cells often have complex internal membranes, In vaginated regions of plasma membrane

Function in respiration or photosynthesis

Prokaryotic Cell Structures 1, Nucleoid region

Contains the single, circular chromosome; May also contain plasmids

Prokaryotic Cell Structures 1, Ribosomes

Smaller than those of eukaryotes; Differ in protein and RNA content; Targeted by some antibiotics

Prokaryotic Cell Structures 2, Internal compartments

Small number of membrane-bounded structures seen

Prokaryotic Cell Structures 2, Magnetosome in

Magnetotactic bacteria

Prokaryotic Cell Structures 2, Protein shells called bacterial microcompartments (BMC)

Isolate specific metabolic processes; Increase concentration of reactants; Protect the cell from toxic metabolic intermediates

Horizontal Gene Transfer, 3 types of horizontal gene transfer

Conjugation, Transduction, Transformation

Horizontal Gene Transfer, All 3 processes also observed in archaea

Also in archaea

Transformation, Natural transformation

Occurs in many bacterial species; DNA from a dead cell picked up by a live cell; Proteins for it are on the bacterial chromosome; Evolved, not an accident of plasmid or phage biology

Transformation, Artificial transformation

Some species do not naturally undergo transformation; Accomplished in the lab; Used to transform E. coli for molecular cloning

Transduction, Generalized transduction

Virtually any gene can be transferred; Occurs via accidents in the lytic cycle; Viruses package bacterial DNA and transfer it in a subsequent infection

Transduction, Specialized transduction

Occurs via accidents in the lysogenic cycle; Imprecise excision of prophage DNA; These phage carry both phage genes and chromosomal genes

Conjugation, Plasmids may encode functions not necessary to the organism, but may provide a selective advantage

Provide selective advantage

Conjugation, In E. coli, conjugation is based on the presence of the F plasmid (fertility factor)

Based on F plasmid

Conjugation, F+ cells contain the plasmid – donor cells; F- cells do not – recipient cells

F+ donors, F- recipients

F plasmid transfer, F+ cell produces F pilus that connects it to F- cell

Produces F pilus

F plasmid transfer, Transfer of F plasmid occurs through conjugation bridge

Through conjugation bridge

F plasmid transfer, F plasmid copied through

Rolling circle replication

F plasmid transfer, The end result is

two F+ cells

F plasmid recombination 1, The F plasmid can integrate into the bacterial chromosome

Can integrate into chromosome

F plasmid recombination 1, Integration events similar to crossing over in eukaryotes; Homologous recombination

Similar to crossing over

F plasmid recombination 1, Hfr cell (high frequency of recombination)

F plasmid integrated into chromosome; Replicated every time host divides

F plasmid recombination 1, The F plasmid can also excise itself by reversing the integration process

Can excise itself

F plasmid recombination 1, An inaccurate excision may occur picking up some chromosomal DNA - F' plasmid

Inaccurate excision creates F' plasmid

F plasmid recombination 2, During conjugation in Hfr strains, the transfer of genes is

linear and progressive

F plasmid recombination 2, Genes farther from the origin of transfer will be transferred later

Farther genes transferred later

F plasmid recombination 2, Different marker genes appear in the

recipient cell at specific times

F plasmid recombination 2, Gene order can be mapped based on entry time

Gene order mapped by entry time

Antibiotic resistance, R (resistance) plasmids

Encode antibiotic resistance genes; Acquire genes through transposable elements

Antibiotic resistance, Genes from pathogenic species transferred by plasmids or transduction

Encode genes for pathogenic traits; Enterobacteriaceae; E. coli O157:H7 strain evolved by acquiring genes for pathogenic traits

Mutations in bacteria, Mutations can arise spontaneously in bacteria as with any organism

Arise spontaneously

Mutations in bacteria, Radiation and chemicals

Increase likelihood for mutations

Mutations in bacteria, Auxotrophs are nutritional mutants

Can no longer survive on minimal medium

Mutations in bacteria, Mutations (and plasmids) can spread rapidly in a population

Spread rapidly

Mutations in bacteria, Examples

Methicillin-resistant Staphylococcus aureus (MRSA); Vancomycin-resistant Staphylococcus aureus (VRSA)

CRISPR systems provide adaptive immunity, Screens of prokaryotic genomes revealed repeated sequences with spacer regions called CRISPR

Clustered
Regularly
Interspaced
Short
Palindromic
Repeats

CRISPR systems provide adaptive immunity, Adaptive immunity to viral infection

Immunity to viral infection

CRISPR systems provide adaptive immunity, Prokaryotes integrate short segments of viral nucleic acid into CRISPR loci, produce RNA that degrades viral nucleic acid

Integrate viral segments, produce degrading RNA

CRISPR systems provide adaptive immunity, Useful for gene editing in the lab

Useful for gene editing

Prokaryotic Metabolism 1, Organisms require carbon for building, a source of electrons to use in redox chemistry, and energy for anabolic processes

Require carbon, electrons, energy