Identifying and Classifying Bacteria

Ch. 23

What is a prokaryote?

Cells that lack a true nucleus.

Cells that lack membrane-bound organelles.

Most surrounded by a cell wall.

Many secrete a protective slime capsule.

How big is a prokaryotic cell?

1- 5 micrometers (1 millionth of a meter)

Classification

Archaebacteria vs Eubacteria

Archaebacteria

Surrounded by a cell wall lacking peptidoglycan.

Live in extreme conditions

Examples of Archae

Methanogens: convert H2

and CO2 into methane gas for energy

Halophiles: love saltThermoacidophiles: love heat and acid

Eubacteria:

Surrounded by a cell wall made of peptidoglycan.

Example: rhizobium- nitrogen–fixing

bacteria

Identifying Prokaryotes

1. Shape:• Coccus – spherical• Bacillus – rod-shaped• Spirillum – spiral• Vibrio – comma shape

Coccus

Spirillum

Vibrio

Bacillus

Ex. Diplococcus

Cocci and Bacilli may group together

Prefixes for arrangements: Diplo – two

Strepto – chain

Streptococcus

Streptobacillus

Staphylo - clustered

Staphylococcus

2. Motility: ability to moveFlagella: whip-like structure used to propel bacteria

Slime: glide along slime secretion

Spiral motion: cork-screw motion (spirillum)

3. Metabolism: Oxygen or NOT

Obligate Aerobes: Need oxygen

Obligate Anaerobes: cannot live in oxygen

Facultative anaerobes: can live with or without oxygen

3.Metabolism: Obtaining EnergyAutotroph vs. Heterotroph• Photoautotroph- uses light

energy for photosynthesis• Chemoautotroph- uses

energy from inorganic chemicals for chemosynthesis

• Photoheterotrophs- uses photosynthesis and eats organic compounds

• Heterotroph – consumes organic compounds

review

What role do chemosynthetic bacteria have in the ecosystem?

http://www.youtube.com/watch?v=4lmwbBzClAc&NR=1

Bacterial Reproduction

Asexual: Binary fission

1. Circular DNA replicates2. Cell membrane and cell

wall divide 3. Identical daughter cells

separate

How fast does this happen?

http://www.youtube.com/watch?v=gEwzDydciWc&feature=related

approximately every 20 minutes

Genetic recombination

Sharing or exchanging of genetic material

3 types:1. Conjugation2. Transformation3. Transduction

1. ConjugationA temporary bridge forms between two cells.

A plasmid, a separate section of DNA, is transferred from one cell to the other.

Often the plasmid contains useful genes, like antibiotic resistance.

2. Transformation

Bacteria takes in DNA from the environment.

Dead bacteria may break apart and release DNA.

Other bacteria can pick up this DNA and become genetically different.

3. Transduction

Viruses can pick up small amounts of DNA from a host bacteria.

When it infects another bacteria, the new DNA is transferred into that cell.

Disease

Pathology is the study of disease.

Pathogens: organisms that cause disease.

Gram-staining Test

Gram-positive: bacteria contain lots of peptidoglycan in cell walls. Stains purple.

Gram- negative: bacteria contain little peptidoglycan in cell walls. Stains red.

Exotoxins

Poisonous proteins that are released by some gram-positive bacteria.

For example Clostridium tetani secretes an

exotoxin that causes tetanus.Tetanus causes stiffness in muscles.

Clostridium botulinum produces a very powerful exotoxin that causes the fatal disease, botulism.

1 g of botulism toxin can kill 1 million people.

Endotoxins

Lipids and carbohydrates in the cell membranes of some Gram-negative bacteria, that are poisonous.

They are released when the bacteria die.

For example:

Most species of Salmonella, are endotoxin producing bacteria.

Salmonella typhi, causes typhoid fever.

AntibioticsAntibiotics interfere with the bacteria’s cellular activities.

For example:Penicillin: blocks the building of the cell wall.“Accidently” discovered by Alexander Fleming in 1920s

Tetracyline: blocks protein synthesis.

Where do antibiotics come from?

Antibiotics are naturally made by some fungi and bacteria.

Some are made synthetically in labs.

But most used in treatment still come from bacteria.

Antibiotic-ResistanceBacteria can quickly adapt to their environment because of their rapid rate of reproduction.

Antibiotic-Resistance1. If one bacterium mutates

and becomes resistant, 2. then in the presence of

antibiotics, bacteria not resistant die

3. Those with the resistance take over the population.

Which diseases are preventable by better sanitation practice?

CholeraSalmonellaTetanusStaph

What are other ways that antibiotic resistance is passed?

Genetic recombination