Prokaryotes• Lack nuclei• Typically lack or have very few internal

membranes• Cytoplasm contains ribosomes, storage granules

that hold glycogen, lipid, or phosphate compounds

• Metabolic enzymes are associated with the plasma membrane, especially where it is infolded to form limited internal membranes – such membranes are generally referred to as a mesosome

• The plasma membrane interacts with the cytoplasm in signaling functions

• Motile bacteria have a corkscrew flagellum

Prokaryotic Organization• Key features

– No nucleus– DNA held in nucleoid– Cytoplasm dense:

• Ribosomes• Storage granules• Limited membranes

– Plasma membrane– Corkscrew flagellum– Cell wall is complex

• Outer membrane• Peptidoglycan layer• Capsule • Pili extend from cytoplasm

Domains of Life

BACTERIA

• ARCHAEBACTERIA– Introns in DNA– Lack peptidogycan

in cell walls– Live in extreme

environments

• EUBACTERIA– Includes most

bacteria– Most have one of

three shapes– May be divided

into up to 12 phyla

– Classification is controversial

Archaebacteria and Eubacteria• Carl Woese has indicated, based on small

subunit ribosomal RNA (SSU rRNA) sequencing, that there are two domains of bacteria

• Archaea – Lack peptidoglycan in cell wall– Produce methane gas– Ether-linked lipids– Live in ‘early Earth’ conditions– Extreme halophiles, thermophiles, and acidophiles

• Eubacteria– Have peptidoglycan in cell wall– Are rifamycin-sensitive (blocks transcription)– All other bacteria

TYPES OF ARCHAEBACTERIA

Thermoacidophilies Living in hot springs

Methanogens living in sewage

Extreme halophile

living in the Great Salt Lake

The Archaea

• Methanogens– Anaerobes– In digestive tracts of animals– Produce methane gas

• Extreme halophiles– Live in saturated salt– Many are photosynthetic

• Extreme thermophiles– Live in hot springs – Often live in acidic environments (acidophiles)

The Eubacteria

• Most abundant bacteria• Important in the biosphere

– Major producer of primary production (of carbon via photosythesis)

– Most numerous organisms in the soil– Most important nitrogen fixing

organisms, often via symbiotic associations• e.g. rhizobial bacteria in root nodules

Bacteria• Bacteria are prokaryotes

– They are cells– They lack nuclei

• There are two professional viewpoints regarding the general, overall classification of prokaryotes:– Some biologists support the concept that they

constitute two domains: Archaea and Eubacteria– Other biologists classify them into two

kingdoms, Archaebacteria and Eubacteria

• Most are very small – 0.5 – 1.0 m in diameter

BASIC SHAPES OF EUBACTERIA

SPHERICALSPHERICAL

ROD-SHAPEDROD-SHAPED

SPIRILLASPIRILLA

Cell Walls

• Provides support for cell• Protects against osmotic shock

– Most bacteria well adapted to hypotonic conditions– Most bacteria grow poorly in hypertonic

conditions; hence jams, salted foods prevent bacterial growth

• Cell wall composition unique to bacteria– Eubacterial cell wall made of peptidoglycan

• Complex of polymerized amino sugars and short polypeptides

• Is really one polymer surrounding the cell

Capsules and Pili

• Many bacteria secrete a capsule, or slime layer– Used to attach, prevent phagocytosis – Can be used to enhance infective

bacteria

• Pili are hair-like appendages– Allow attachment to surfaces– Are sometimes involved in bacterial

conjugation (sexual activity that involves the transfer of DNA)

The Bacterial Flagellum• Rotates • Is corkscrew-shaped• Three parts:

– Basal body– Hook– Filament (made of one

protein: flagellin)

• Cell uses ATP to pump protons out

• Protons diffuse through membrane at basal body

• Breakdown of gradient converted to rotation

The Gram Stain• Bacterial cell wall differences can be used to

identify and categorize cells• 1888: Christian Gram developed the Gram

Stain– Some bacteria retain crystal violet stain after

alcohol wash• Called gram-positive

– Other cells referred to as gram-negative

• Stain retention determined by cell wall organization– Gram-positive cells have thick peptidoglycan wall– Gram-negative cells have outer membrane and thin

peptidoglycan layer

Gram-positive and Gram-negative Cell Walls

Most Species of Eubacteria may be Grouped Based on Staining

• Gram-Negative

– Lack thicker layer of peptidoglycan

– Stain pink

– Endotoxins

• Gram-Positive– Thicker layer of

peptidogycan– Stain purple– Exotoxins

(released when bacteria die)

Gram- negativeGram- negativeGram-positiveGram-positive

Giant Bacterium• But size is not an indicator; Epulopiscium fishelsoni is a

giant bacterium from the gut of the surgeonfish• Here, ~ 600 m long and 80 m wide, much larger than

the large protist Paramecium (other cells in picture)

Nutrition and Growth

• Saprophtes ex: decomposers• Photoautotrophs ex: blue-green algae• Obligate anaerobes ex: tetanus• Facultative anaerobes ex: E.Coli• Obligate aerobes ex: tuberculosis• Thermophilic bacteria

Most bacteria grow at at neutral pH but some grow best at a pH of 6 or lower– Bacteria that produce yogurt and sour cream

Anabaena: a Eubacterium• Complex, free-living &

photosynthetic• A cyanobacterium• The larger cells fix nitrogen, are

oxygen-sensitive

Bacterial Chromosome

• Bacteria have a circular genomic DNA molecule -– Single chromosome– ~1000X longer than cell if stretched out

• Also have plasmids– Small, circular DNA fragments– Can replicate independently of the

genomic DNA or be integrated into genomic DNA

– Carry genes for resistance, for genetic exchange or for enzymes

Bacterial Sexual Reproduction• Most simply put, sex is transfer of genetic

information.• Three mechanisms known for bacterial

sexual reproduction:– Transformation

• Bacteria take up DNA from environment• Griffith’s 1928 experiment with S and R bacteria

showed that DNA was heritable substance

– Transduction• Genes are transferred through phage (next slide)

– Conjugation • Two cells of opposite mating type come together,

form pili bridges bridges through which DNA is transferred

Conjugation of E. coli

Bacterial Pathogens

• Some are disease-causing agents– Most bacteria are not harmful– Many have positive relationship with

hosts – e.g. human gut microbe E. coli– But many are pathogenic– Cause serious disease:

• Cholera • Diphtheria• Tuberculosis

Antibiotics

• Antibiotics are drugs that combat bacteria by interfering with cellular functions– Penicillin – interferes with cell wall

production– Tetracycline – interferes with protein

production– Sulfa drugs – produced in the

laboratory– Broad-spectrum antibiotics will affect

a wide variety of organisms

Endotoxins• Pathogenic bacteria can produce exotoxins,

which increase their success but tend to be very damaging to the host– Often the toxin, not the bacterial infection, is most

dangerous– Examples:

• Diphtheria toxin• Botulism toxin

• Endotoxins: – Not secreted but are components of the cell wall– Affect host when released from dead bacteria– Can bind macrophage, cause the release of fever-

inducing agents– Resistant to heating

Commercial Bacteria• Bacteria used in many commercial processes

– Lactic acid bacteria convert lactic acid to simpler monomers

• Used in yogurt, acidophilous milk for lactose-intolerant people

– Bacteria used for making • Cheeses • Fermented meats such as salami• Pickling agents such as vinegar

– Bacteria also used to make pharmaceutical agents– Also used as means to make biomedical agents

and biological molecules– Used also to reduce pollution – as bioremediation

agents

Penicillin

• This amazing fungus produces the famous antibiotic, penicillin. In 1928. Alexander Fleming observed that a mold called Penicillium notatum produced a substance, later known as penicillin, that killed bacteria in its presence. This antibiotic was the first of many to be found and used to treat infections.

• Interferes with cell wall production.

This fungus makes antibiotics and This fungus makes antibiotics and cheese. Other varieties of the cheese. Other varieties of the fungus produce blue cheese and fungus produce blue cheese and Roquefort cheeses.Roquefort cheeses.

Koch’s Postulates

• Robert Koch, late 19th Century• Defined conditions likely to identify a

pathogen1. Present in all infected individuals2. Sample of the micro organism can be

grown in culture from the host3. Culture produces disease in a second

host4. Microorganism can be recovered from

second, experimentally created host