Chp 27

Bacteria & Archaea

Rob Swatski

Assistant Professor of Biology

HACC – York Campus

Overview: Masters of Adaptation

• Prokaryotes thrive almost everywhere, including

places too acidic, salty, cold, or hot for most other

organisms

• Most prokaryotes are microscopic, but what they lack

in size they make up for in numbersin size they make up for in numbers

• They have an astonishing genetic diversity

• There are more in a handful of fertile soil than the

number of people who have ever lived!!!

Structural & functional adaptations

contribute to prokaryotic success

• Prokaryotes are divided into two domains: Bacteria &

Archaea

• Most prokaryotes are unicellular, although some

species form coloniesspecies form colonies

• Most prokaryotic cells are 0.5–5 µm, much smaller than

the 10–100 µm of many eukaryotic cells

Bacteria on Cheek

Epithelial Cells - 5500X

• Prokaryotic cells have a variety of shapes

- the 3 most common shapes are spheres (cocci), rods

(bacilli), & spirals

(a) Spherical(cocci)

1 µm

(b) Rod-shaped(bacilli)

2 µm

(c) Spiral

5 µm

Cell-Surface Structures

• An important feature of nearly all prokaryotic cells is their cell

wall

- maintains cell shape

- provides physical protection

- prevents the cell from bursting in a hypotonic environment

• Eukaryote cell walls are made of cellulose or chitin• Eukaryote cell walls are made of cellulose or chitin

• Bacterial cell walls contain peptidoglycan

- network of sugar polymers cross-linked by polypeptides

Peptidoglycan animation

• Archaea contain polysaccharides & proteins but lack

peptidoglycan

• Using the Gram stain, scientists classify many

bacterial species into Gram-positive & Gram-

negative groups based on cell wall composition

• Gram-negative bacteria:• Gram-negative bacteria:

- have less peptidoglycan

- outer membrane can be toxic

- more likely to be antibiotic resistant (many

antibiotics target peptidoglycan & damage cell

walls)

Cellwall Peptidoglycan

layer

Plasma membrane

Outermembrane

Carbohydrate portionof lipopolysaccharide

Protein

(b) Gram-negative: crystal violet is easily rinsed

away, revealing red dye.

Cell

wall

Peptidoglycan

layer

Plasma membrane

ProteinProtein

(a) Gram-positive: peptidoglycan traps

crystal violet. (P = “+” purple)

Gram-positive

bacteria

Gram-negativebacteria

20 µm

Fimbriae

Capsule

Cell wall

Circular chromosome

Sex pilus

Internalorganization

Flagellae

Sex pilus

Capsule: polysaccharide or protein layer

covers many prokaryotes

Capsule

Some prokaryotes also have fimbriae (attachment pili)

- allows them to stick to substrates or to other individuals in colony

Sex pili are longer than fimbriae

- allow prokaryotes to exchange DNA

Fimbriae, UTI's, & Cranberry Juice

Fimbriae

Motility

• Most motile bacteria propel themselves by flagella -

structurally & functionally different from eukaryotic

flagella

• Many bacteria exhibit taxis, the ability to move toward

or away from certain stimulior away from certain stimuli

Chemotaxis!

Flagellum

Filament

HookCell wall

50 nm

Hook

Basal apparatus

Plasmamembrane

Internal & Genomic Organization

Prokaryotic cells usually lack complex compartmentalization

But, some do have specialized membranes that perform

metabolic functions

Respiratorymembrane

0.2 µm 1 µm

(a) Aerobic prokaryote (b) Photosynthetic prokaryote

Thylakoidmembranes

membrane

• The prokaryotic genome has less DNA than the

eukaryotic genome

• Most of the genome consists of a circular chromosome

- the DNA is not surrounded by a membrane & is

located in a nucleoid region

• Some species of bacteria also have smaller rings of DNA

called plasmids

Chromosome Plasmids

1 µm

Reproduction & Adaptation

• Prokaryotes reproduce quickly by binary fission and can

divide every 1–3 hours

• Many form metabolically inactive endospores

- can remain viable in harsh conditions for centuries- can remain viable in harsh conditions for centuries

Endospore

Endospore formation in Lyme bacteria

0.3 µm

Prokaryotes can

evolve rapidly

because of their

short generation

times

EXPERIMENT

RESULTS

Daily serial transfer

0.1 mL(population sample)

Old tube

(discardedaftertransfer)

New tube

(9.9 mL

growthmedium)

Fit

ne

ss r

ela

tiv

eto

an

cest

or

Generation

0 5,000 10,000 15,000 20,000

1.0

1.2

1.4

1.6

1.8

Prokaryotes have considerable genetic variation

3 factors contribute to this genetic diversity:

- Rapid reproduction

- Mutation

- Genetic recombination

Rapid Reproduction & Mutation

• Prokaryotes reproduce by binary fission

- offspring cells are generally identical

• Mutation rates during binary fission are low, but

because of rapid reproduction, mutations can because of rapid reproduction, mutations can

accumulate rapidly in a population

• High diversity from mutations allows for rapid

evolution

Binary Fission in Bacteria

Genetic Recombination

Prokaryotic DNA from different individuals can be brought

together by:

- transformation

- transduction

- conjugation- conjugation

Transformation: a cell takes up & incorporates foreign

DNA from the surrounding environment

Transformation in Bacteria

animation

Transduction: the movement of genes between bacteria

by bacteriophages (viruses that infect bacteria)

Bacteriophage animation

Donorcell

A+B+

A+ B+

Phage DNATransduction

Recombinant cell

Recipientcell

A+ B–

B–

A+

A–

Recombination

A+

Conjugation:

- DNA is transferred between bacterial cells

- Sex pili allow cells to connect & pull together for DNA

transfer

• A piece of DNA called the “F” factor is required for the • A piece of DNA called the “F” factor is required for the

production of sex pili

- the F factor can exist as a separate plasmid or as DNA

within the bacterial chromosome

Sex pilus 1 µm

The “F” Factor as a Plasmid

“F” factor is transferable during conjugation as an F plasmid

• Cells with the F plasmid function as DNA donors during

conjugation

• Cells without the F plasmid function as DNA recipients• Cells without the F plasmid function as DNA recipients

during conjugation

F plasmid

F+ cell

Matingbridge

Bacterial chromosome

F+ cell

Conjugation & recombination of an F plasmid in E. coli

F– cell

bridge

Bacterialchromosome F+ cell

The F- cell is the DNA recipient

The “F” Factor in the Chromosome

• A cell with the F factor built into its chromosomes

functions as a DNA donor during conjugation

• The recipient becomes a recombinant bacterium, with

DNA from 2 different cells

F factor

Hfr cell

A+

A+

A+

A+

RecombinantF– bacterium

A– A+

Conjugation & transfer of part of an Hfr

bacterial chromosome in E. coli

F factorA–

F– cell

A– A+ A–

4 Major Modes of Nutrition

• Photoautotrophy: obtain energy from light

• Chemoautotrophy: obtain energy from chemicals

• Photoheterotrophy: require CO2 as a carbon source• Photoheterotrophy: require CO2 as a carbon source

• Chemoheterotrophy: require an organic nutrient to

make organic compounds

The Role of Oxygen in Metabolism

• Obligate aerobes: require O2 for cellular respiration

• Obligate anaerobes: are poisoned by O2 & use

fermentation or anaerobic respiration

• Facultative anaerobes: can survive with or without O2

Nitrogen Metabolism

• Prokaryotes can metabolize nitrogen in a variety of ways

• Nitrogen fixation: convert atmospheric nitrogen (N2) to

ammonia (NH3)

Metabolic Cooperation

• Metabolic cooperation: allows prokaryotes to use

environmental resources they could not use as individual

cells

• In the cyanobacterium Anabaena, photosynthetic cells &

heterocytes (nitrogen-fixing cells) exchange metabolic heterocytes (nitrogen-fixing cells) exchange metabolic

products

Cyanobacteria!

Photosyntheticcells

Heterocyte

20 µm

Metabolic cooperation can occur in surface-coating

colonies called biofilms

Your Own Personal Biofilm! Tooth Biofilm video

Look Look

Closer!!!

Molecular systematics is illuminating

prokaryotic phylogeny

Before the late 20th century, systematists based prokaryotic

taxonomy on phenotypic criteria

Applying molecular systematics to prokaryotic phylogeny

has produced dramatic resultshas produced dramatic results

- has led to a phylogenetic classification of prokaryotes

- major new clades have been identified

UNIVERSALANCESTOR

Eukaryotes

Korarcheotes

Euryarchaeotes

Crenarchaeotes

Nanoarchaeotes

Do

ma

inE

uk

ary

aD

om

ain

Arch

ae

a

ANCESTOR

Proteobacteria

Chlamydias

Spirochetes

Cyanobacteria

Gram-positivebacteria

Do

ma

in B

acte

ria

The use of polymerase chain reaction (PCR) has allowed

for more rapid sequencing of prokaryote genomes

- A handful of soil many contain 10,000 prokaryotic

species!!!

Horizontal gene transfer between prokaryotes obscures

the root of the tree of life

PCR Animation

Archaea

Archaea share certain traits with Bacteria & other traits

with Eukarya

Eukarya

Archaea

Bacteria

Extremophiles: live in harsh environments

• Extreme halophiles: live in very saline environments

• Extreme thermophiles: thrive in very hot environments

Extremophile Archaea

Acid-Loving Archaea

<Sniff> <Sniff> ... Do you

smell something?

• Methanogens live in swamps & marshes

- produce methane as a waste product

- strict anaerobes & are poisoned by O2

In recent years, genetic prospecting has revealed many

new groups of Archaea

- some may offer clues to the early evolution of life

54

Rhizobium (arrows) inside a rootcell of a legume (TEM)

2.5

µm

Soil bacterium Nitrosomonas

- converts NH4+ to NO2

–

Slime-secreting myxobacteria

Fruiting bodies ofChondromyces crocatus, amyxobacterium (SEM)

B. bacteriophorus

Bdellovibrio bacteriophorus

attacking a larger bacterium(colorized TEM)

5 µ

m

Pathogens

- Campylobacter (blood poisoning)

- Helicobacter pylori (stomach ulcers)

Helicobacter pylori

Spirochetes

Helical heterotrophs

- Treponema pallidum (syphilis)

- Borrelia burgdorferi (Lyme disease)

Cyanobacteria

Photoautotrophs that generate O2

Plant chloroplasts likely evolved from cyanobacteria

- endosymbiosis

1 µ

m

Hundreds of mycoplasmascovering a human fibroblastcell (colorized SEM)

Chemical Cycling

Chemoheterotrophic prokaryotes: decomposers

- break down corpses, dead vegetation, & wastes

Nitrogen-fixing bacteria: Nitrogen-fixing bacteria:

- add usable N to the environment

Ecological Interactions

Symbiosis:

- larger host

- smaller symbiont

Mutualism:

Commensalism:Commensalism:

Parasitism:

http://www.youtube.com/watch?v=UXl8F-eIoiM

Pathogenic Prokaryotes

Pathogenic prokaryotes typically cause disease by:

Exotoxins:

- cause disease even if the prokaryotes that produce

them are not present

Endotoxins:

- released only when bacteria die & cell walls break down

Prokaryotes in Research & Technology

Biotechnology

Bioremediation

Bioremediation

Other Uses of Prokaryotes:

- Mining

- Vitamin synthesis

- Antibiotics & hormone synthesis