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1

Four Importance of Microorganisms


▪ Microorganisms are foundation for all life on Earth

▪ Have existed for ~3.5 billion years

▪ Plants, animals, modern microorganisms all evolved from ancestral bacteria

▪ Our life depends on their activities

2

Spontaneous Generation Detractors

– Francesco Redi
– Louis Pasteur
– John Tyndal

3

Louis Pasteur

▪ Considered the father of modern microbiology
▪ French chemist
▪ Demonstrated air is filled with microorganisms
▪ Filtered air through cotton plug
▪ Observed trapped microorganisms
▪ Many looked identical to those found in broths

4

John Tyndall

▪ Realized broths made from hay contained heat- resistant microbes.

▪ English physicist

5

Golden Age of Microbiology

The principle that microorganisms cause diseases is known as Germ Theory of Disease.

Most pathogenic bacteria identified (1875–1918)
• Work on viruses began
• Understanding that microscopic agents could cause disease led to control efforts
• Huge improvements in past century in human health
• Antibiotics to treat infectious diseases
• Vaccines to prevent diseases

6

Emerging diseases

Changing lifestyles increase opportunities to spread
• Closer contact with animals (e.g., hantavirus)
• Evolution of infectious agents previously unable to infect humans
(e.g., HIV/AIDS, SARS, Ebola virus)

7

Re-emerging diseases

• Vaccination can become victim of own success
• Lack of firsthand knowledge of dangers of diseases can lead people to fear vaccines more than the diseases
• Diseases such as measles, mumps, whooping cough nearly eradicated from U.S. but could re-emerge with declining vaccination rates

8

Microorganisms in the Environment

▪ Recycling of nutrients
▪ Oxygen production through photosynthesis
▪ Nitrogen fixation
▪ Decomposers of material
▪ Cellulose degraded in the environment and in the digestive tracts of ruminants

9

Members of the Microbial World

Two basic cell structures
▪ Prokaryotes: Do not have a membrane-bound nucleus
▪ Eukaryotes: Have a membrane-bound nucleus and organelles
▪ All living things can be classified into one of three groups, or domains:
▪ Bacteria ▪ Archaea ▪ Eukarya

10

Domain Bacteria

• Single-celled prokaryotes
• Prokaryote = “prenucleus”
• No membrane-bound nucleus
• No other membrane-bound organelles
• DNA in nucleoid
• Most have specific shapes (rod, spherical, spiral)
• Rigid cell wall contains peptidoglycan (unique to bacteria)
• Multiply via binary fission
• Many move using flagella

11

Domain Archaea

▪ Like Bacteria, Archaea are prokaryotic
• Similar shapes, sizes, and appearances to Bacteria • Multiply via binary fission
• May move via flagella
• Rigid cell walls
▪ However, major differences in chemical composition
• Cell walls lack peptidoglycan
• Ribosomal RNA sequences different
▪ Many are extremophiles
• High salt concentration, temperature

12

Domain Eukarya

• Eukaryotes = “true nucleus”
• Membrane-bound nucleus and other organelles
• More complex than prokaryotes
• Microbial members include fungi, algae, protozoa
• Algae and protozoa also termed protists
• Some multicellular parasites including helminths (roundworms, tapeworms) considered as well

13

Eukarya

Eukaryotic ribosomes are 80S
• Important medically: antibiotics impacting 70S ribosome do not affect 80S ribosomes

▪ Fungi
• Diverse group
• Single-celled (e.g., yeasts) or multicellular (e.g., molds, mushrooms)
• Energy from degradation of organic materials
• Primarily live on land

▪ Algae
• Diverse group
• Single-celled or multicellular
• Photosynthetic
• Contain chloroplasts with chlorophyll or other pigments
• Primarily live in water
• Rigid cell walls
• Many have flagella
• Cell walls, flagella distinct
from those of prokaryotes

▪ Protozoa
• Diverse group
• Single-celled
• Complex, larger than prokaryotes
• Most ingest organic compounds
• No rigid cell wall
• Most motile

14

Morphology of Prokaryotic Cells

▪ Two types most common
• Coccus: spherical
• Rod: cylindrical
▪ Variety of other shapes
• Vibrio, spirillum, spirochete
• Pleomorphic (many shapes)
• Great diversity often found in low nutrient environments

Prokaryotic ribosomes are 70S
• Made from 30S and 50S

Most prokaryotes divide by binary fission

15

Gram-Negative

Pink

Thin layer of peptidoglycan

Bilayer made from lipopolysaccharide (LPS)

LPS is called endotoxin

Includes Lipid A (immune system recognizes) and O antigen (can be used to identify species or strains)

16

Gram-Positive

Purple

Thick layer of peptidoglycan

17

Peptidoglycan

• N-acetylmuramic acid (NAM)

• N-acetylglucosamine (NAG)

• Tetrapeptide chain (string of four amino acids) links glycan chains

18

Antibacterial Substances That Target Peptidoglycan

▪ Peptidoglycan
• Can weaken to point where unable to prevent cell lysis
▪Penicillin interferes with peptidoglycan synthesis
• Prevents cross-linking of adjacent glycan chains
• effective against Gram-positive bacteria than Gram-negative bacteria
• Outer membrane of Gram-negatives blocks access • Derivatives have been developed that can cross
▪ Lysozyme breaks bonds linking glycan chain
• Enzyme found in tears, saliva, other bodily fluids
• Destroys structural integrity of peptidoglycan molecule