Host Defense

Animals – immune system– RNA interference

(RNAi)• Dicer – dsRNA

nuclease

• siRNA – short interfering RNA

• RISC – RNA-induced silencing complex

• Slicer – ssRNA nuclease

Dicer

siRNA

mRNA

RISC

dsRNA

Dicer cleaves dsRNAinto shorter segments

RNA fragments degraded by Slicer

RISC cleaves mRNA

RISC complex findsmRNA complementary

to siRNA

RISC complexbinds siRNA and

separates thestrands

Fig. 8.16

Fig. 20-7a in the 11th edition

Chemical antimicrobial agents used to control microorganisms that are harmful to humans:

Sterilants destroy all forms of microbial life

Disinfectants kill microorganisms, but endospores are typically resistant

Sanitizers reduce the microbial load but may not eliminate all microorganisms

Antiseptics & Germicides

kill or inhibit growth of microorganisms on living tissue

;

1929 discovered antimicrobial effects of penicillin G made by the fungus Penicillium on Staphylococcus by chance

1945 Nobel Prize in Medicine - Fleming, Howard Walter Florey and Ernst Boris Chain

1888-1955 Alexander Fleming

Vancomycin

• Glycopeptide antibiotic

• Binds to pentapeptide of the peptidoglycan precursor

• Produced by a soil microbe Amycolatopsis orientalis

• Effective against Gram-positive Bacteria

Platensimycin

• Produced by Streptomyces platensis

• Inhibits fatty acid biosynthesis enzyme

Fig. 27.25

An example of an echinocandin

An example of a polyoxin

Bacterial cell with chromosomal mutation

altering target of antibioticBacterial cell not

resistant to antibiotic

Transfer of free DNA

Previously susceptible cell is now resistant to antibiotic

Transformation

Lysis of cell

resistant to antibiotic

Bacterial cell with R plasmid resistant to antibiotic

Bacterial cell not resistant to antibiotic

Copy and Transfer of R plasmid

Previously susceptible cell is now resistant to antibiotic

Chromosomal DNA Conjugation

Key:

Gram-negative

Gram-positive

Gram-positive/acid-fastFungus

Candida albicans *

Acinetobacter sp.

Enterococcus faecium*

Streptococcus pneumoniae

Mycobacterium tuberculosis*

Haemophilus ducreyi

Salmonella typhi

Haemophilus influenzae

Neisseria gonorrhoeae

Pseudomonas aeruginosa*

Salmonella sp.

Shigella dysenteriae

Shigella sp.

Other gram-negative rods

Staphylococcus aureus*

1950 1960 1970 1980 1990 2000 2010

Year

Antimicrobial drug resistance human pathogens continue to emerge.

Fig. 27.29

Fig. 14.7Comparable to Fig. 11.8 in the 11th edition

Billionyears ago

Extinction of the dinosaurs

Phanaerozoic

Eon Evolutionaryevent

Oxygenlevel

Metabolic andother highlights

Proterozoic

Archaean

Hadean

Cambrian

Precambrian

20%

10%

Early animals

Multicellulareukaryotes

First eukaryotes

Great oxidationevent

Cyanobacteria

Purple and greenbacteria

1%

0.1%

Ozone shield

(2H2O

Oxygenic photosynthesis

O2 + 4H)

Anoxic (H2S

Anoxygenic photosynthesis

S0 + 2H)

(CO2 + 4H2

Methanogenesis CH4 + 2H2O)

First cellularlifeFormation ofcrust and ocean

Formation of Earth

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Fig. 11-9 in the 11th edition

(aerobic)

(oxygenic)

The Hydrogen Hypothesis – how the first eukaryotic was formed?

Symbiont cell - Bacteria producing H2; lipid gene transfer; precursor of mitochondrion

Host cell - Archaea dependent on H2 for electron source to make energy

Symbiont cell – photosynthetic cyanobacterial-like ancestor

outgroup

Fig. 14.14

Fig. 14.15

Fan-shaped

Dichotomous

Internal nodes denote common ancestor

Branches show order of descent and node ancestry.Branch length reprepresents number of nucleotide changes

Nodes at the tips denote species/strains

Fig. 14.14d

Fig. 11.20 in 11th edition

Fig. 11.21 in 11th edition