18.4 Bacteria and Archaea KEY CONCEPT Kingdoms Eubacteria and Archaeabacteria are composed of single-celled prokaryotes

18.4 Bacteria and Archaea

KEY CONCEPT Kingdoms Eubacteria and Archaeabacteria are composed of single-celled prokaryotes.


Prokaryotes are widespread on Earth.

• Prokaryotes can be grouped by their need for oxygen. – obligate aerobes

are need oxygen

– facultative aerobes can live with or without oxygen

– obligate anaerobes are poisoned by oxygen


• Eubacteria and Archaebacteria are structurally similar but have different molecular characteristics.

flagellum

pili

plasmid

cell wall

chromosome

plasmamembrance

This diagram shows the typical structure of a prokaryote. Archaea and bacteria look very similar, although they have important molecular differences.

– plasmid (circular DNA)

– flagellum – Pili (genetic

exchange)


Domain Archaea, Kingdom Archaebacteria

• Archaebacteria are typically obligate anaerobes.• Live in extremely harsh environments, ex.stomachs of

cows, high salt concentrated areas such as the Dead Sea and in sulfur springs or deep sea vents.

• Divided into 3 groups: methanogens (methane producers, halophiles (salt loving) and thermophiles (heat loving)

• Come in a variety of shapes, similar to Eubacteria.• There is no peptidoglycan in their cell walls, contain

entirely different lipids than Eubacteria.• ***Eubacteria is actually evolutionary older than

Archeabacteria


• Eubacteria commonly come in three forms. – rod-shaped, called bacilli

Lactobacilli: rod-shaped Spirochaeta: spiral

– spiral, called spirilla or spirochetes

– spherical, called cocci

Enterococci: spherical

Domain Bacteria, Kingdom Eubacteria


Eubacteria groups (prefixes describe bacteria)

• Diplo: two

• Staphlo: cluster

• Strepto: chain

• Ex. Diplococcus

• Ex. Staphlospirlli

• Ex. Streptobacillus


Eubacteria

GRAM NEGATIVE GRAM POSITIVE

– The amount of peptidoglycan within the cell wall can differ between Eubacteria: Gram negative has extra outer membrane, Gram positive cell wall just peptidoglycan


• Gram staining identifies bacteria.

Gram-negative bacteria have a thin layer of peptidoglycan and stain red.

Gram-positive bacteria have a thicker peptidoglycan layer and stain purple.

– stains polymer peptidoglycan – gram-positive stains purple, more peptidoglycan – gram-negative stains pink, less peptidoglycan


Bacteria have various strategies for survival.

• Form of genetic recombination is conjugation.– Prokaryotes

exchange genes using pili

conjugation bridge

TEM; magnification 6000x


Other forms of genetic exchange

• Transduction: exchange of genes using a virus• Transformation: endocytosis of DNA


Bacteria survival

• Bacteria may survive by forming endospores.– Resistant to most

cleaning agents and temperature changes

– Creates double membrane around DNA to survive harsh conditions

– Sterilize versus disinfect?


Prokaryotes provide nutrients to humans and other animals. • Prokaryotes live in digestive systems of animals.

– make vitamins and medicines– break down food – fill niches (role in ecosystem)


• Bacteria help ferment many foods.– yogurt, cheese– pickles, sauerkraut – soy sauce, vinegar


Prokaryotes play important roles in ecosystems.

• Prokaryotes have many functions in ecosystems. – photosynthesize – recycle carbon, nitrogen,

hydrogen, sulfur – fix nitrogen (make it useable)


• Bioremediation uses prokaryotes to break down pollutants.

– oil spills

– biodegradable materials


Some bacteria cause disease.

• Bacteria cause disease by one of two methods:– invading tissues

– making toxins (poison released by an organism)


– immune system may be lowered

• Normally harmless bacteria can become destructive.


Ex. Tuberculoses (Mycobacterium tuberculosis)

• Bacteria multiply in the lungs, killing WBCs• Host releases histamines which cause swelling


Ex. Staph poisoining (Staphylococcus aureus)

• Food poisoning caused by mishandling of food• Infection of the skin


Ex. Botulism (Clostridium botulinum)

• Improperly canned foods contaminated with endospores


Ex. Flesh eating bacteria (Streptococci)

• Colonize tissue through cut or scrape


Antibiotics are used to fight bacterial disease.

• Antibiotics may stop bacterial cell wall formation. • Their role is to interfere with the ability of the bacteria’s

reproduction process.


Overuse of Antibiotics

• Bacteria become resistant due to exposure

• Kill the weak bacteria while stronger bacteria become resistant

Underuse of Antibiotics

Misuse of Antibiotics

• Viruses cannot be treated with antibiotics, allowing normal bacteria to become resistant or killing them


Bacteria can evolve resistance to antibiotics.

1. Bacterium carries genes for antibiotic resistance on a plasmid (circular DNA).

2. Copy of the plasmid is transferred through conjugation (using pili).

3. Resistance is quickly spread through many bacteria.

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18.4 Bacteria and Archaea KEY CONCEPT Kingdoms Eubacteria and Archaeabacteria are composed of single-celled prokaryotes