Chapter 19Bacteria and

Viruses

Section 19-1 Learning Targets

• Explain how the two groups of prokaryotes differ

• What are the factors used to identify prokaryotes

• Explain why bacteria are vital to the living world.

Classification• DOMAINS of Prokaryotic Organisms

1. BACTERIA: Contain peptidoglycan in cell walls

2. ARCHAEA: Do not contain peptidoglycan in cell walls.

• KINGDOMS of Prokaryotic Organisms 1. Eubacteria

• Live almost everywhere – soil; intestines of animals.

• Cell wall with peptidoglycan – a carbohydrate.

– EX: Escherichia coli (E. coli) – necessary for digestion in humans but can cause disease.

Structure of Eubacterium

Peptidoglycan Cell Wall Cell Membrane

Ribosome

Flagellum DNA Pili

Classification, cont’d.• KINGDOMS of Prokaryotic Organisms,

cont’d. 2. Archaebacteria

• Live in extremely harsh environments –hot springs; Great Salt Lake; mud.

• Cell walls without peptidoglycan.– EX: Methanogen – produce methane gas in guts of

animals.

Hot Spring inYellowstone

National Park

Identification of Prokaryotes

• Prokaryotes are identified by:– Shape– Cell wall structure– Ways they move– Ways they obtain energy

Shape• Cocci (Singular: coccus)

– Round/spherical shape• Can form long chains or clumps/clusters

– EX: Streptococcus and Pneumococcus form long chains

Streptococcus pneumoniae

--Chain of cocci that causes pneumonia

Staphylococcus: Clusters of cocci.

Diplococcus: A pair of cocci – can cause pneumonia

Causes staph infections – “boils”

Shape• Bacilli (Singular: bacillus)

– Rod-shaped bacterial cells• EX: E. coli found in the human intestine

Shape• Spirilla (Singular: spirillum)

– Spiral and corkscrew-shaped bacteria• EX: Syphilis (an STD caused by bacteria)

Cell Wall Structure• Two types of cell walls in Eubacteria

– A method called Gram staining is used to tell them apart• Cell walls containing mainly peptidoglycan

– Called Gram positive Bacteria» Peptidoglycan in the cell wall only picks up

the purple stain (appear purple under microscope)

» Not as resistant to antibiotics

• Cell walls with a second, outer layer of lipid and carbohydrate

– Called Gram negative Bacteria» Wall only absorbs the red stain (appear pink

under microscope)» More resistant to antibiotics

Movement• Prokaryotes can also be identified by

the way they move– Some propelled by flagella

• Flagella: whip-like structures used for movement

– Others lash or spiral forward – Some glide using slime they secrete– Others do not move at all

Forms of Nutrition• Prokaryotes have diverse

adaptations that allow them to live in any environment– There are two types of prokaryotes

based on the ways that they obtain energy

– Autotrophs and Heterotrophs

Forms of Nutrition cont’d• AUTOTROPHS: Make their own food

– Photoautotrophs: Use light to make food• Found where light is plentiful, near surfaces of

lakes, streams and oceans– EX: Cyanobacteria

– Chemoautotrophs: obtain energy directly from inorganic compounds such as hydrogen sulfide (H2S)

• Get energy from chemical reactions• Found deep in the darkness of the ocean

Forms of Nutrition• HETEROTROPHS: Obtain food from

other sources • MOST bacteria are heterotrophs!

– Chemoheterotrophs: use organic molecules for energy•EX: Staphylococcus aureus

– Gets energy from food and release chemicals that cause food poisoning

•EX: Salmonella, Clostridium botulinus

– Photoheterotrophs: VERY unusual•Use light for energy and inorganic

molecules for nutrition

Respiration• Obligate Aerobes: Must have oxygen

– EX: Tuberculosis infects lungs

• Obligate Anaerobes: Do not tolerate oxygen– EX: Tetanus bacteria; botulism.

• Facultative anaerobes: Do not require oxygen but are not harmed by it either– Found in many environments.

Bacterial Growth• When conditions are favorable, bacteria

can grow and divide at astonishing rates!

• Some as often as every 20 minutes….which means in just 48 hours the bacteria would reach a mass approximately 4000 times the mass of Earth!!!

Bacterial Growth and Reproduction

•There are three ways bacteria grows and reproduces.–Binary Fission–Conjugation–Spore Formation

Reproduction/Growth• Binary Fission: Divides into two; asexual

– Most reproduce through binary fission

Reproduction/Growth

• Conjugation: Transfer of genetic material– Bridge forms between two cells,

genes move from one cell to the other

– Considered sexual-- increases genetic diversity

– Can lead to antibiotic resistance in some bacteriaConjugation

Bridge

Reproduction/Growth

• Spore Formation– When growth conditions become

unfavorable, many bacteria form spores• Spores called endospores when a thick

wall encloses DNA and cytoplasm– Endospore can remain dormant until more

favorable growth conditions arise– Dangerous; require high

temperatures and pressures to destroy

Anthrax Endospore

Roles of Bacteria in Nature1. Decomposers: Bacteria that help the

ecosystem recycle nutrients– They break down dead matter into

simpler substances– Bacteria are important in sewage

decomposition

• Example: rotten log; dead carcasses.

Roles of Bacteria in Nature2. Aid in Digestion: In humans, termites and

other organisms– EX: E. coli in human intestine– EX: Bacteria that digest cellulose in

termites

Roles of Bacteria in Nature

3. Nitrogen Fixation: Process of converting nitrogen into a form plants can use- Plants need nitrogen to make amino acids

for proteins.– The nitrogen in the air cannot be used by

plants until it is “FIXED” into ammonia or other nitrogen compounds

– Bacteria fix the nitrogen for the plants to use

Nitrogen Fixation Example

•Soybeans host the nitrogen-fixing bacteria Rhizobium on their roots.

Roles of Bacteria in Nature4. Cause Disease: Only pathogenic

bacteria cause disease (not all bad!)- Cause disease by damaging tissues

or releasing toxins that harm the body

- Treat with antibiotics: penicillin, tetracycline- Antibiotics: block growth and

reproduction of bacteria

Tooth decay

Lyme disease

Tetanus

Tuberculosis

Salmonella food poisoning

Pneumonia

Cholera

Streptococcus mutans

Borrelia burgdorferi

Clostridium tetani

Mycobacterium tuberculosis

Salmonella enteritidis

Streptococcus pneumoniae

Vibrio cholerae

Regular dental hygiene

Protection from tick bites

Current tetanus vaccination

Vaccination

Proper food-handling practices

Maintaining good health

Clean water supplies

Disease Pathogen Prevention

Roles of Bacteria in Nature5. Food Production: Bacteria used in the

production of cheese, yogurt, vinegar and sour cream– Bacteria cause fermentation

6. In Industry: Bacteria can digest petroleum, remove waste from water and help mine minerals from ground

7. Biotechnology: Bacteria may be genetically engineered to produce medicines

Roles of Bacteria in Nature8. Control Methods:

A. Disinfectants – alcohol, lysol;antiseptics

B. High heat and high pressuresC. Freezing – does not kill but

controlsD. Drying, salting, pickling,

preserving with sugarE. Canning – pressure cookerF. Antibiotics

9. Germ Warfare: A. Anthrax – can be aerosolized and

is very hardy --Three days without treatment - death--Can be treated with antibiotics.

Anthraxinfection

Bacillus anthracis