Archaebacteria&

Bacteria

Classification• Old 5 Kingdom system

• Monera, Protists, Plants, Fungi, Animals

• New 3 Domain system– reflects a greater

understanding of evolution & molecular evidence• Prokaryote: Bacteria

• Prokaryote: Archaebacteria

• Eukaryotes– Protists

– Plants

– Fungi

– Animals

Prokaryote

Eukaryote

Fig. 27-2

(a) Spherical (cocci)

1 µm

(b) Rod-shaped (bacilli)

2 µm

(c) Spiral

5 µm

Structure and Function

• 3 basic shapes: spherical (cocci), rods (bacillus) and spiral

• Cell Wall– Peptidoglycan covers cell, anchors

attachments– Archaea have no peptidoglycan

Gram Staining

Gram + : simple walls, lots of PTG

Gram - : complex walls with lipopolysaccharides less PTG

– Medical significance: Gram – lipids are toxic causing fever or shock and are resistant to our defenses

– Gram –: antibiotic resistance (hard for drugs to penetrate)

– Antibiotics often target peptidoglycan

peptide sidechains

cell wallpeptidoglycan

plasma membrane

protein

Gram-positive bacteria

Gram-negative bacteria

peptidoglycan

plasmamembrane

outermembrane

outer membrane of lipopolysaccharides

cell wall

peptidoglycan = polysaccharides + amino acid chainslipopolysaccharides = lipids + polysaccharides

Prokaryote Cell Wall Structure

Fig. 27-4

Capsule

200 nm

Capsule vs Fimbriae

• Sticky and covers entire cell

• Protection from dehydration and shield from immune system

• Hair like appendages that stick

• Ex. Neisseria gonorrhoeae sticks to mucus membranes

• Shorter and more numerous than sex pilli

Fig. 27-5

Fimbriae

200 nm

Motility for most bacteria

• propel themselves by flagella that are structurally and functionally different from eukaryotic flagella

• PROK flagella are 1/10 the width of EUK• PROK flagella are not covered by plasma

mem

Motility

• Different composition and propulsion• The motor of the flagella is the basal apparatus

(rings embedded in the cell wall) • ATP proton pump generates power by turning

hook attached• Hook is attached to chains of flagellin

• In a heterogeneous environment, many bacteria exhibit taxis, the ability to move toward or away from certain stimuli

Video: Prokaryotic Flagella (Video: Prokaryotic Flagella (Salmonella typhimuriumSalmonella typhimurium))

Fig. 27-6

Flagellum

Filament

Hook

Basal apparatus

Cell wall

Plasmamembrane

50 nm

Fig. 27-8

Chromosome Plasmids

1 µm

chloroplast

mitochondria

internal membranes

for respiration

like a mitochondrion

(cristae)

internal membranes

for respiration

like a mitochondrion

(cristae)

internal membranesfor photosynthesislike a chloroplast(thylakoids)

internal membranesfor photosynthesislike a chloroplast(thylakoids)

cyanobacterium(photosythetic) bacterium aerobic bacterium

Variations in Cell Interior

Reproduction and Adaptation

• Binary fission in optimal conditions every 1-3 hours (E.coli every 20 min usually 1/24 hr)

• They are small, repro binary fission and short generation time

• Endopsores (ability to endure hardship)

Fig. 27-10EXPERIMENT

RESULTS

Daily serial transfer

0.1 mL(population sample)

Old tube(discardedaftertransfer)

New tube(9.9 mLgrowthmedium)

Fit

nes

s re

lati

veto

an

ces

tor

Generation0 5,000 10,000 15,000 20,000

1.0

1.2

1.4

1.6

1.8

Rapid Evolution: high genetic diversity

• 2 strains of E.coli differ in an rRNA gene more than between a human and a platypus

• Rapid reproduction

• Mutation

• Genetic recombination

Mutation

• Probability of a spontaneous mutation in an E.coli gene is 1 in 10 million/division

• 2x1010 new E.coli per day

• About 2000 bacteria will have mutations

• 4300 genes total in E.coli

• 4300 x 2000 = 9 million mutation per day in the human intestines

Genetic Recombination

• Transformation: uptake foreign DNA– Ex. Competent cells, pneumonia

• Transduction: a bacteriophage performs horizontal gene transfer

• Conjugation

• Plasmids

Fig. 27-11-4

Recombinant cell

Recipientcell

A+ B–

B–

A+

A–

Recombination

A+

Donorcell

A+ B+

A+ B+

Phage DNA

Conjugation and Plasmids

• Conjugation is the process where genetic material is transferred between bacterial cells

• Sex pili allow cells to connect and pull together for DNA transfer

• 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

Fig. 27-12

Sex pilus 1 µm

The F Factor as a Plasmid• Cells containing the F plasmid function as

DNA donors during conjugation• Cells without the F factor function as DNA

recipients during conjugation• The F factor is transferable during

conjugation

Fig. 27-13

F plasmid

F+ cell

F– cell

Matingbridge

Bacterial chromosome

Bacterialchromosome

(a) Conjugation and transfer of an F plasmid

F+ cell

F+ cell

F– cell

(b) Conjugation and transfer of part of an Hfr bacterial chromosome

F factor

Hfr cell A+A+

A+

A+

A+A– A– A–

A– A+

RecombinantF– bacterium

R Plasmids and Antibiotic Resistance

• R plasmids carry genes for antibiotic resistance

• Antibiotics select for bacteria with genes that are resistant to the antibiotics

• Antibiotic resistant strains of bacteria are becoming more common

Bacterial Diversity

Major nutritional modesRole of oxygen in metabolismNitrogen metabolism

nitrogen fixation: converting N2 from the atmosphere into ammonia NH3

Metabolic Cooperation colony of cyanobacterium Anabaena (filaments) genes for photosynthesis (most cells) and N fixation)few heterocytes) but one cell cannot perform both

Biofilms

Table 27-1

Fig. 27-14

Photosyntheticcells

Heterocyte

20 µm

Prokaryotic phylogeny• Horizontal gene

transfer (ring instead of a tree)

• Archaea more closely related to eukaryotes than bacteria

• polyphyletic

Eukarya

Archaea

Bacteria

Archaea

Eukarya

Bacteria

Fig. 27-16

UNIVERSALANCESTOR

Eukaryotes

Korarcheotes

Euryarchaeotes

Crenarchaeotes

Nanoarchaeotes

Proteobacteria

Chlamydias

Spirochetes

Cyanobacteria

Gram-positivebacteria

Do

main

Eu

karyaD

om

ain A

rchaea

Do

main

Bacteria

Table 27-2

Proteobacteria• These gram-negative bacteria include

photoautotrophs, chemoautotrophs, and heterotrophs

• Some are anaerobic, and others aerobic

Fig. 27-18a

Alpha

Beta

Gamma

Delta

Epsilon

Proteobacteria

Subgroup: Beta Proteobacteria

Nitrosomonas (colorized TEM)

1 µ

m

Subgroup: Delta Proteobacteria

10 µ

m

Fruiting bodies ofChondromyces crocatus, amyxobacterium (SEM)

Bdellovibrio bacteriophorusattacking a larger bacterium(colorized TEM)

5 µ

m

Helicobacter pylori (colorized TEM)

2 µ

m0.

5 µ

m

Subgroup: Epsilon Proteobacteria

B. bacteriophorus

Thiomargarita namibiensiscontaining sulfur wastes (LM)

Subgroup: Gamma Proteobacteria

Subgroup: Alpha Proteobacteria

Rhizobium (arrows) inside aroot cell of a legume (TEM)

2.5

µm

Subgroup: Alpha Proteobacteria• Many species are closely associated with

eukaryotic hosts• Scientists hypothesize that mitochondria

evolved from aerobic alpha proteobacteria through endosymbiosis

• Example: Rhizobium, which forms root nodules in legumes and fixes atmospheric N2

• Arrows in the next slide are Rhizobium

• Example: Agrobacterium, which produces tumors in plants and is used in genetic engineering

Fig. 27-18c

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

2.5

µm

Cyanobacteria

• These are photoautotrophs that generate O2

• Plant chloroplasts likely evolved from cyanobacteria by the process of endosymbiosis

Two species of Oscillatoria,filamentous cyanobacteria (LM)

Concept 27.6: Prokaryotes have both harmful and beneficial

impacts on humans• Some prokaryotes are human pathogens, but others have positive interactions with humans• Prokaryotes cause about half of all human diseases• Lyme disease is an example

Fig. 27-21

5 µm

• Pathogenic prokaryotes typically cause disease by releasing exotoxins or endotoxins

• Exotoxins 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

• Many pathogenic bacteria are potential weapons of bioterrorism