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