BacteriaBiology 11

Prokaryotic Cells

• Unicellular• No nucleus• No membrane-bound organelles• Do contain DNA

2 Kingdoms• Archaebacteria “ancient bacteria”• Eubacteria “true bacteria”

Archaebacteria: The Extremists

• Live in harsh environments

1. Methanogens: – Produce methane– Live in oxygen free environments– Found in swamps, marshes, stomachs of

cows– Sewage disposal plants- help breakdown

sewage

2. Halophiles: Salt-loving • Live in salt pools left after a lake has

evaporated–pools have high levels of magnesium and

potassium salts–Utah’s Great Salt Lake and Middle East’s

Dead Sea

3. Thermoacidophiles: Heat- and acid-loving – Live around deep ocean vents– Temperatures are often above 100ºC–Anaerobic (without oxygen)– Live in hot, acidic waters of sulfur springs

Eubacteria• Live everywhere except extreme

environments

1. Heterotrophs–Use organic molecules as food source– Some are parasites – Some are saprophytes (feed on dead

organisms or organic wastes – break down and recycle nutrients)

2. Photoautotrophs–Photosynthetic autotrophs - Live in places

with sunlight–Cyanobacteria – contain chlorophyll

(pigment) that traps the sun’s energy • Live in ponds, streams, and moist areas of land• Composed of chains of independent cells

3. Chemoautotrophs–Make organic molecules–Obtain energy by breaking down compounds

with sulfur and nitrogen and releasing the energy in the process called chemosynthesis–Bacteria in Plants– able to convert atmospheric

nitrogen into the nitrogen-containing compounds that plants need

Bacteria Structure• Ribosomes- protein

synthesis• Chromosome-

single circular DNA molecule

• Cell Wall- support and protection

• Flagella- motility

• Pilli (sing. Pillus) hair like structure to aid in reproduction and attaching to one another

• Capsule- sticky, gelatinous, surrounds cell wall to protect against desiccation

• Cytoplasm- thick liquid within cytoplasmic membrane

• Plasmid- small circular piece of DNA

If Bacteria don’t have mitochondria, how do they get their energy?

• Occurs at cell membrane

Identifying Bacteria• Bacteria are separated into two groups based

on characteristics of cell wall• Cell walls made of peptidoglycan (sugar and

amino acid molecules) which helps structure and maintain shape (target for antibiotics)

• Technique called gram staining is used to do this

Gram Stain• First, crystal violet dye is added. Then, a second

dye is added.• Gram + bacteria retain crystal violet dye• Gram – bacteria appear red or pink after a

counterstain is added (commonly safranin)

1. Gram-positive: one thick layer of peptidoglycan (protein and sugar)

2. Gram-negative: one thin layer of peptidoglycan and an outer lipid and sugar layer

Identifying Bacteria• Bacteria shape (plural)– Cocci (spheres)– Bacilli (rods)– Spirilla (spirals)

Growth patternDiplo (paired arrangement)Staphylo (grape arrangement)Strepto (chain of cells)

Strepto-Coccus

Strepto-Bacillus

Spirillum

How do bacteria get around?

• Flagella vs Cilia

• Flagella use whip like motions to move

• Cilia use a beating motion to move (eukaryotes only)

Remember:• Bacterial DNA– Circular– Free floating in the bacterial cytoplasm

A well fed bacteria is two happy bacteria

• ATP- when used, turns into ADP (Tri-phosphate or Di-phosphate)

• Bacteria have a protein called DnaA that starts the process of DNA replication (first step in fission)

• DnaA+ADP = nothing ; DnaA+ATP = replication

Bacteria Reproduction1. Asexual by binary fission–DNA replicated–DNA pulled to separate poles as

bacterium increases in size–A partition forms and separate the

cells–Results in genetically identical cells–Can be rapid –ideal conditions every

20 minutes

Plasmids• Extra circle of DNA that can replicate

independently • Can be transferred to another Bacterium• Typically carries a beneficial trait. e.g.

antibiotic resistance.

2. Conjugation• Bacteria conjugate if one of them have special

“F” factor (fertility factor)

• The F+ bacteria (donor) makes a Pilus, and transfers the F plasmid to the F- recipient.

• Recipient is now F+

• Results in a bacteria with new genetic composition

Spore Formation• Endospore: tiny structure that contains a

bacterium’s DNA and a small amount of its cytoplasm– Encased by tough outer covering–Resists drying out, extreme temperature,

harsh chemicals– If environmental conditions improve, then

endospore germinate– To kill endospores, items must be sterilized

(i.e. heated under high pressure)

Metabolism

• 2 Types: Aerobic and Anaerobic

• Aerobic Bacteria require oxygen to produce energy

• Anaerobic Bacteria don’t require oxygen to produce energy

• When typing Bacteria- Gram’s stain is #1, then comes how they make energy

• Obligate Anaerobic (Can’t live with oxygen)• Facultative Anaerobic (can get by either way)• Obligate Aerobic (Can’t live without oxygen)

Where can they get energy from?

Importance of Bacteria

Ecological Role1. Production of nutrients

a) Nitrogen fixationb) Vitamin K, B12c) Breakdown of cellulose

2. Breakdown of detritus3. Prevention of pathogen colonization

Production of Nutrients• Soil microbes take nitrogen from atmosphere

and make nitrogen containing compounds (nitrates, nitrites, etc)

• Some exist in symbiotic relationships (eg. Termites, legumes, clover, alder, etc)

• Some bacteria produce Vitamin K (E. coli) or B12, which are not produced anywhere else

• Cellulose (plant fibers) cannot be broken down by eukaryotes

• Many organisms exist in symbiotic relationships with bacteria in order to break down cellulose into usable sugars.

Break down of detritus

• Bacteria clear landscape of dead matter

• Returns nutrients to the soil

Prevention of colonization

• Take up valuable real estate that pathogenic organisms would love to inhabit

• Harmless or beneficial bacteria prevent harmful ones from colonizing