1/23/2019

1

Bacteria and

Archaea

Learning Objectives

• At the end of this unit, a student should be able to…

• Describe characteristics of prokaryotic cells and distinctions among

major groups of bacteria

• Explain the basis and rationale for the classification system of bacteria

• Describe the structure and common shapes of prokaryotic cells

• Compare the cell wall of gram-positive and gram-negative bacteria

• Summarize the three forms of genetic recombination in prokaryotes

• Describe the factors that contribute to the rapid evolution of bacteria

(and antibiotic resistance)

• Identify ecological roles of bacteria

• List Koch’s postulates

• Identify adaptations that have contributed to pathogen success

• Describe various specialized ecological niches of archaea

History of classification

• Until the middle of 20th century, all life was thought

to belong to two groups

(whatever was not

animals, including fungi,

algae and bacteria)

Animals Plants

LIFE

History of classification

• Then… two main groups based on the cell type

• (complex eukaryotic cells, and simple prokaryotic cells)

LIFE

Eukarya Prokarya

History of classification

• In late 1970s, Carl Woese & colleagues discovered

two distinctly different groups of “prokaryotes”

• proposed “Domains”

LIFE

Eukarya

Prokarya

Archaea Bacteria

Animals

Plants

Fungi

Protists

Three Domain System

• like all good science,

this discovery was

reported and the

domains were

proposed via primary

scientific literature

Carl Woese

1/23/2019

2

Three Domain System

Carl Woese

• Based on ribosomal RNA data,

two distinctly different groups of

‘prokaryotes’ exist

• These prokaryotic organisms

were as biochemically and

genetically different from each

other as they were from any

eukaryote

Three Domain System

Examples of phylogenetic trees (cladograms) depicting

the relationships among the domains

“Prokaryotes”

• Two domains • Bacteria

• Archaea

• Defining characteristics • Small (length < 5μm)

• Single celled organisms

• Simple cells

• No nucleus

• one circular chromosome

• No membrane-bound organelles

3 Domains

• “Prokaryotes”

• Domain Bacteria

• cell walls have peptidoglycan

• Domain Archaea

• cell walls do not have peptidoglycan

• Domain Eukarya (eukaryotes) • includes animals, plants, fungi, protists

(Prokaryotic cells are difficult to distinguish as

bacteria or archaea morphologically)

Bacterial Morphology

Fig. 24-9, p. 513

Outer membrane

Pili

(structures

used for

attachment)

Peptidoglycan

layer

Cell wall

Nuclear

area

(nucleoid)

Storage granule

Plasmid

(DNA) Flagellum

Ribosomes

Bacterial chromosome

(DNA) Capsule

Plasma

membrane

1/23/2019

3

• 3 basic shapes

Coccus (spherical)

Bacterial Morphology

Bacillus (rod shaped) Spiral (helical) Spirillum - rigid

Spirochete - flexible

Staphylococcus aureus

Bacterial Morphology

Concept of bacterial species

• Bacterial species • a population of cells with similar characteristics

• A pure culture of bacteria is often a clone

• descendants of one cell

• Why would the concept of “species” be

different for bacteria?

Concept of bacterial species

• Bacteria do not

reproduce sexually!

• Exchange genes

between distantly

related species • antibiotic resistance

• rapid evolution

Fig. 24-14b, p. 517

F+ (donor) cell F– (recipient) cell

1 F+ (donor) cell produces

sex pilus.

Bacterial

chromosome

F plasmid

2 Sex pilus develops into

conjugation bridge.

DNA replicates, and single

strand of F plasmid DNA is

transferred from F+ cell to F–

cell.

3

Both bacterial cells now

contain double-stranded F

plasmid. The F– cell has been

converted to an F+ cell.

4

Conjugation Concept of bacterial species

• pure cultures of the same

species are not always

genetically identical

• Domain:

• Kingdom:

• Phylum

• Class

• Order

• Family

• Genus

• Species

• Strain/phylotype

1/23/2019

4

Bacterial strain

E. coli O157:H7 is a cousin of the regular E.coli living

in our intestines. They share less than 50% DNA

sequence similarity.

Bacterial strain

Methicillin-resistant Staphylococcus aureus (MRSA)

Staphylococcus aureus

vs.

CLASSIFICATION OF BACTERIA

•Bergery’s Manual of Systematic Bacteriology

•About taxonomic classification of the bacteria

•Bergey’s Manual of Determinative Bacteriology

•Tells how to identify bacteria using biochemical and molecular biology methods

Bacterial Classification

Based on a “gram-stain” • Can be divided into two classes • gram-positive

• gram-negative

• Cell Wall

contains

peptidoglycan • penicillin disrupts

peptidoglycan

production

Bacterial Reproduction

• Bacteria reproduce quickly • ex. E. coli divides every 20 minutes at 370 C

• Binary Fission

• cell divides into two equal “daughter cells”

Bacterial Genes

• Genetic material in bacteria • Chromosome

• 1 circular DNA molecule

• Plasmids

• 1 or more smaller circular DNA fragments

• NOT chromosomes

• often not “essential” for bacterium

1/23/2019

5

Exchange of Genetic Material

• Transformation • bacterial cell takes in DNA fragments released by another

cell

• Transduction • phage carries bacterial DNA from one bacterial cell into

another

•Conjugation • two cells of different mating types exchange genetic

material

1 Bacterium dies and releases DNA.

2 Fragments of foreign DNA bind to

proteins on surface of living

bacterium.

3 DNA enters cell, and some DNA is

incorporated into host cell by

reciprocal recombination.

DNA exchanged

Transformation

1 DNA of a phage

penetrates bacterial

cell.

2 Phage DNA may become

integrated with host-cell

DNA as a prophage.

Phage DNA with

bacterial genes

3 When the prophage

becomes lytic, bacterial DNA

is degraded and new phages

are produced. New phages

may contain some bacterial

DNA. Fragmented

bacterial DNA

Transduction

Fig. 24-13b, p. 516

4 Bacterial cell lyses and releases

many phages, which can then

infect other cells.

5 Phage infects new host cell.

6 Bacterial genes introduced into new

host cell are integrated into host's

DNA. They become a part of

bacterial DNA and are replicated

along with it.

Fig. 24-14b, p. 517

F+ (donor) cell F– (recipient) cell

1 F+ (donor) cell produces

sex pilus.

Bacterial

chromosome

F plasmid

2 Sex pilus develops into

conjugation bridge.

DNA replicates, and single

strand of F plasmid DNA is

transferred from F+ cell to F–

cell.

3

Both bacterial cells now

contain double-stranded F

plasmid. The F– cell has been

converted to an F+ cell.

4

Conjugation Aerobes and Anaerobes

• Aerobic bacteria • require oxygen for cellular respiration

• Facultative anaerobes • metabolize anaerobically when necessary

• Obligate anaerobes • only metabolize anaerobically

1/23/2019

6

Metabolic Diversity

Chemical reactions Light

Organic

compounds

chemoheterotroph photoheterotroph

Carbon Dioxide chemoautotroph photoautotroph

Energy Source

Carb

on

So

urc

e

Ecological Roles

• Essential decomposers • recycle nutrients

• Photosynthesis • capture sun’s energy

• Nitrogen fixation • convert atmospheric Nitrogen to usable forms

• Symbiotic with other organisms

Symbiosis

• Mutualism • both partners benefit

• Commensalism • one partner benefits

• other not harmed or helped

• Parasitism • parasite benefits at expense of host

BACTERIA AND DISEASE •Pioneers in microbiology

•Anton van Leeuwenhoek

•discovery of the cell

•Louis Pasteur

•germ theory

•pasteurization

•Robert Koch

•Koch’s postulates

Basically, each

disease is caused by a

specific pathogen

KOCH’S POSTULATES •Guidelines used to demonstrate that a specific pathogen causes specific disease symptoms:

•The pathogen must be present in every individual with the disease

•A sample of the microorganism taken from the diseased host can be grown in pure culture

•A sample of the pure culture causes the same disease when injected into a healthy host

•The microorganism can be recovered from the experimentally infected host

Antibiotic Resistance

• Overuse of antibiotics • main cause of drug

resistance

• Example of Natural

Selection • bacteria that are not

resistant are killed

• resistant bacteria multiply

and produce a resistant

population

1/23/2019

7

Antibiotic Resistance

• Plasmids may have genes for antibiotic

resistance (R factors) • transfer resistance to other bacteria

• Example: Methicillin-

resistant Staphylococcus

aureus (MRSA) and

vancomycin-resistant S.

aureus (VRSA) • directly linked to horizontal

transfer of antibiotic resistance

through conjugation

Antibiotic Resistance

• 1 in every 100 healthy

people in the US now

carry MRSA

• MRSA causes more

than 90,000 serious

infections and more than

17,000 deaths each

year

• Many bacteria in watery environment form

dense biofilms that attach to solid surfaces • communities of microorganisms

• many species of bacteria

• may include archaea, fungi, and protozoa

• Example: dental plaque that forms on teeth

Antibiotic Resistance

Archaea

Haloquadratum walsbyi

Pyrococcus furiosus

Archaea

• Archaea are best known to

inhabit extreme environments

• Two major phyla • Crenarchaeota

• mainly extreme thermophiles

• Euryarchaeota

• methanogens

• extreme halophiles

• extreme thermophiles

Archaea

• Extreme thermophiles

• can live at temperatures

greater than 80°-100° C • Pyrolobus fumarii

• led scientists to extend the upper

temperature limit for life to 113° C.

• Pyrococcus furiosis

• source of an extra-stable enzyme

that can endure the process of

PCR, the method behind gene

sequencing and DNA

fingerprinting

• grows optimally at 100 degrees

Celsius

1/23/2019

8

Archaea

• Hyperthermophiles

• live at temperatures up to 121° C • Cell walls don’t melt

• Proteins and DNA don’t denature

How?

Archaea

• Extreme

halophiles • Inhabit saturated salt

solutions

• Live in salt ponds, the

Dead Sea, and Great

Salt Lake

Archaea

• Methanogens • produce methane

• (natural gas)

• decompose compounds

rich in carbon/hydrogen

• inhabit anaerobic

environments

• swamps

• sewage

• digestive tracts

Methanopyrus kandleri

Archaea

• Methanogens • The methanogens in the rumen of a cow are estimated

to release about 50 liters of methane a day.

• Methanogens produce more than two billion tons of

methane each year

skinnyde - flickr

Archaea

• Symbiosis • Like bacteria, archaea often

form mutualistic relationships

• e.g. methanogens and cows

• Unlike bacteria, archaea do

not have pathogenic or

parasitic relationships

skinnyde - flickr

Archaea