Bacteria

Bacteria
• Are the most numerous organisms on
Earth!
• Were probably the first forms of life.
Fossils indicate they were about 1 billion years before eukaryotes.
• Are prokaryotes (no nucleus)
• Have been found almost everywhere!

Bacteria are very small!

Classification of Bacteria
• Must use the RNA sequences to classify them. • Two Kingdoms:
– Eubacteria (typical bacteria we encounter)
– Archaebacteria (more ancient)
• Methanogens (live in bottoms of swamps) • Halophiles (live in salty conditions)
• Thermoacidophiles (acidic, hot areas)

Shapes of Bacteria
• Bacilli
– Rod shaped

• Cocci
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–
–
–

Sphere shaped
May be streptococci if in a chain
May be diplococci if in pairs of two
May be staphlococci if in grape-like clusters

• Spirilla
– Spiral shaped

Gram Stain Classification
• Bacteria species are often grouped into two categories based on a laboratory technique called Gram staining
• Gram-positive retain the Gram stain & appear purple
• Gram-negative do not retain the stain and appear pink from a secondary stain.

Gram Positive & Gram Negative Bacteria

Gram-positive and gram-negative bacteria differ in…
• Cell walls thickness (gram + has thicker cell wall but gram – has an outer membrane)
• Susceptibilities to antibacterial drugs • The toxic material they produce • Their reactions to disinfectants

Bacteria Phyla:
• Cyanobacteria (blue green algae)
– Photosynthetic, no nucleus or chloroplasts • Spirochetes
– Gram negative, spirals, corkscrew movement • Gram Positive bacteria
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–
–

Not all are, but DNA is similar
Lactobacilli cause tooth decay
Actinomycetes form branching filaments

Bacteria Phyla:
• Proteobacteria
– Enteric (gut) bacteria
– Chemoautotrophs – feed off chemicals E. coli

Sec. 2: Biology of Bacteria
• Structure:
– Cell wall made of peptidoglycan
(short chains of amino acids and carbohydrates) •Gram negative bacteria have outer membrane of lipids and sugars that protects them from some antibiotics.

Cell Wall Structures: + and -

Biology of Bacteria
• Structure:
– Cell Membrane
•Composed of lipid bilayer
•Since bacteria have no mitochondria the cell membrane has enzymes that perform cellular respiration.
•Photosynthetic bacteria perform photosynthesis on thylakoid folds Biology of Bacteria
• Structure:
– Cytoplasm
• Contains ribosomes and DNA
• No membrane bound organelles
• DNA is found in main chromosome and also plasmids
(in some bacteria)

Biology of Bacteria
• Structure:
– Capsule
•An outer covering made of polysaccharides to protect it from dry conditions
•May be made of fuzzy, sticky sugars that help it to attach to surfaces of host cells

Biology of Bacteria
• Structure:
– Pili
•Short, hairlike structures that help bacteria to adhere to host cells. •May be used to transfer genetic material from one bacteria to another.

Biology of Bacteria
• Structure:
– Endospores
•Dormant structure to help bacteria survive in harsh conditions (high temps, harsh chemicals, radiation, drying)
•When favorable conditions return the bacteria will multiply again. Biology of Bacteria
• Structure:
– Movement Structures
•May have flagella (one or several) •May use slime layer to “glide”
•Wavelike contractions to
“propel”

Bacteria motility

Bacteria Structure

Nutrition and Growth
• Food getting:
– May be heterotrophic (saprophytes) and feed on dead and dying material
– May be autotrophic if they can use sunlight (cyanobacteria – simple algae)
– May be chemoautotrophic – they use chemicals for energy (nitrobacter in soil breaks down ammonia

Nutrition and Growth
• Oxygen Relationships:
– May be obligate anaerobes:
• Cannot survive in presence of oxygen (ex. tetanus bacteria)

– May be facultative aerobes
• Can live with or without oxygen
(ex. E. coli)

– May be obligate aerobes
• Cannot live without oxygen (ex.
Bacterium tuberculosis)

Growth Cycle of a Bacterial Culture
1. LAG PHASE: Growth is slow at first, while bacteria acclimate to the food and nutrients in new habitat. 2.