Prokaryotes: BacteriaChapter 18

Two Domains of Bacteria

Domain Archaea Only one kingdom: Archaebacteria

▪ Cells contain cell walls▪ Live in extreme environments (hot, acidic,

salty, no O2)▪ Thermoacidophiles (example: Staphylothermus

marinus in hot sea vents; pictured below)▪ Halophiles (example: Dead Sea bacteria)▪ Methanogens (example: sewage treatment

bacteria)

Two Domains of Bacteria

Domain Eubacteria Only one kingdom: Eubacteria

▪ Very strong cell walls containing peptidoglycan (a polymer)

▪ Cannot survive in extreme environments▪ Can be photosynthetic (autotrophs)▪ Examples:

▪ Anabaena (autotrophs) ▪ Mycobacterium tuberculosis (heterotroph)

Anabaena

Mycobacterium

tuberculosis

Bacteria Structure

• No nucleus, just a chromosome

• Unicellular organisms. They have some characteristics of all cells, such as DNA and ribosomes.

• Lack a nuclear membrane and other membrane-bound organelles

Bacteria Structure

• Chromosomes: large, circular and found in a nucleoid

• Capsule: secreted layer of polysaccharides outside of the cell wall that prevents the cell from drying out and helps it attach to surfaces

• Pili: tiny, hairlike protein structures that help attach to surfaces; can transfer genetic info across them

• Size: VERY small; much smaller than eukaryotic cells

Identifying Bacteria

Three criteria: Shape Cell Wall Movement

Identifying Bacteria: Shape

Three common bacteria shapes: Spherical = Cocci Rod-shaped = Bacilli Spiral-shaped = Spirochetes

Cocci Bacilli Spirochetes

Identifying Bacteria: Cell Walls Gram staining: a dye is added to a

sample of bacteria; peptidoglycan is indicated with purple color

Two Categories: Gram positive: Turns purple during Gram

staining; indicates high level of peptidoglycan in the cell wall

Gram negative: Turns light pink during Gram staining; indicates a low level of peptidoglycan in the cell wall

Identifying Bacteria: Movement

Three common modes of movement: Stationary: no movement Flagella: filament that moves like a tail

to propel the bacteria through an environment

Gliding: secrete a slime layer to glide across

Bacteria Reproduction

Prokaryotes reproduce by: Binary Fission

▪ Division of the cell into two genetically identical cells

▪ Occurs quickly (can be every 20 minutes)

▪ 1 bacterium can become 1 billion in 10 hours

Conjugation▪ Two prokaryotes attach to each other

and exchange genetic information using pili

▪ New gene combinations result in increased diversity

Metabolism of Bacteria

All living things require energy to carry out cellular respiration.

Two categories of obtaining energy: Heterotrophs: cannot make their own food;

must take in food from surroundings▪ Saprobes: decompose organic molecules in dead

organisms or organic waste Autotrophs: make their own food

▪ Photoautotrophs: carry out photosynthesis; require light

▪ Chemoautotrophs: break down inorganic compounds; do not require light

Survival Mechanisms of Bacteria

How can bacteria survive when their surroundings become unfavorable? Two methods of survival:

▪ Endospores: production of a “dormant” cell▪ Mutations: new combinations of genes and

rapid reproduction

Survival: Endospores

1.Spore coat surrounds chromosome and small cytoplasm.

2.Endospore protected if bacteria cell dies.

3.Endospore grow. (germinates)

4.New bacterial cell outgrowth.

Ecology of Bacteria

Bacteria is significant in recycling nutrients to the environment. Decomposer – Breaks down dead

organisms to return organic compounds to the environment.

Nitrogen-fixing – Converts N2 gas in the atmosphere to NH3 (ammonia); allows nitrogen to be taken into the food chain via plants; N is key in amino acids therefore proteins.

Good Bacteria

Most of the bacteria that live in or on you are harmless and are called normal flora.

E. coli 21,674x

Good Bacteria

Some food are made with the aid of bacteria: Cheese Yogurt Buttermilk Pickles Vitamins Chocolate

Pathogens – Bad Bacteria

Disease-causing bacteria are called pathogens.

Antibiotics are used to treat bacterial infections.

Body Story - Salmonella