Prokaryotes A Quick Tour

Bacteria Video  Bacteria Video Bacteria Video Bacteria Video

Bacteria on the point of a pin They are small

“Heat-loving” prokaryotes (a Nevada geyser basin-water temp=104 o C) They are found everywhere that there is life

The three domains of life

Classification schemes

A Comparison of the Three Domains of Life

Diversity of Form and Function

The most common shapes of prokaryotes Coccus Rod Spiral

Cell Surface (1)  Cell wall –Peptidoglycan (found only in eubacteria) –Gram stain –LPS (lipopolysaccharide)  Gram negative bacteria have an outer membrane containing LPS (endotoxin)

Gram-positive and gram-negative bacteria

Gram-positive and gram-negative bacteria Gram-positive and gram-negative bacteria

Cell Surface (2)  Capsule –A gelatinous secretion of some prokaryotes which provides additional protection and helps them to adhere to surfaces and to form aggregates

Cell Surface (3)  Pili –Surface appendages used for adherence to a host or surface. –Sex pilus provides means for transfer of DNA during conjugation

Pili

Motility (1)  Flagella –Rotate rather than whip –Thinner than eukaryotic flagella –Not covered by an extension of the plasma membrane

Form and function of prokaryotic flagella Form and function of prokaryotic flagella

Prokaryotic flagella Prokaryotic flagella

Prokaryotic flagella (Bacillus) Prokaryotic flagella (Bacillus)

Motility (2)  Gliding –Some bacteria move by gliding through a layer of slimy chemicals secreted by the bacteria

Motility (3)  Taxis –Movement toward (positive) or away from (negative) a stimulus –Phototaxis –Chemotaxis

Genome  One double stranded circular chromosome  Chromosome is concentrated in a region of the cell called the Nucleoid region.  Very little protein is associated with the bacteria DNA  Plasmids- small rings of DNA having supplemental (nonessential) genes

Growth, Reproduction, and Gene exchange (1)  Reproduction by binary fission (no mitosis/no meiosis)  Generation time is widely variable –Short generation times allow prokaryotic populations to adapt to rapidly changing environmental conditions. New mutations are screened by natural selection very rapidly

Growth, Reproduction, and Gene exchange (2)  Endospores –A protective mechanism available to some Gram positive organisms to survive adverse environmental conditions. –Resistent to heat, dessication, chemicals –May remain dormant for years

An anthrax endospore

Endospores Endospores

Growth, Reproduction, and Gene exchange (3)  Genetic recombination methods –Transformation –Transduction –Conjugation

Prokaryote colonies in culture Prokaryote colonies in culture

Bacterial and fungal colonies Bacterial and fungal colonies

Nutrition and Metabolism (1)  Photoautotrophs  Chemoautotrophs  Photoheterotrophs  Chemoheterotrophs

Major Nutritional Modes

Nutrition and Metabolism (2) Chemoheterotrophs  Saprobes –Decomposers that absorb nutrients from dead organic material  Parasites –Absorb nutrients from living hosts

Nutrition and Metabolism (3)  Nitrogen metabolism –Eukaryotes can only use nitrogen in certain forms to build proteins and nucleic acids. Prokaryotes can metabolize most nitrogen compounds –Nitrogen Fixation is Unique to certain prokaryotes and is the only mechanism that makes atmospheric nitrogen available to living things for incorporation into organic molecules

Nutrition and Metabolism (4)  Oxygen and growth –Obligate aerobes  Require oxygen, use cellular respiration –Facultative anaerobes  Use oxygen when it is available, but in its absence can grow using fermentation –Obligate anaerobes  Poisoned by oxygen  Live by fermentation or anaerobic respiration

Mini-tour of prokaryote groups

Major groups of prokaryotes

Domain Archaea  Cell walls lack peptidoglycan  Many inhabit the most extreme environments on earth  Methanogens –Use H 2 to reduce CO 2 to CH 4 –Some are used as decomposers in sewage treatment  Extreme Halophiles –High salt environments (15-20%)  Extreme thermophiles

Extreme halophiles Seawater evaporation ponds, used for commercial salt preparation. Colors are from growth of extreme halophiles. Salinity is 15-20%

Hot springs, home of thermophiles

Five of the Major Clades of Bacteria 1. Proteobacteria 2. Gram-positive bacteria 3. Cyanobacteria 4. Spirochetes 5. Chlamydias

Cyanobacteria  Photoautotrophs with plantlike photosynthesis  Chloroplasts evolved from a cyanobacterium that lived as an endosymbiont within a larger host cell  Capable of Nitrogen Fixation

One of the most independent organisms on earth: Cyanobacteria (Anabaena) One of the most independent organisms on earth: Cyanobacteria (Anabaena)

Cyanobacteria: Gloeothece (top left), Nostoc (top right), Calothrix (bottom left), Fischerella (bottom right) Cyanobacteria: Gloeothece (top left), Nostoc (top right), Calothrix (bottom left), Fischerella (bottom right)

A bloom of cyanobacteria A bloom of cyanobacteria

Miscellaneous Topics (1)  Chemical cycles –Prokaryotes are critical links in the recycling of chemical elements between the biological and physical components of ecosystems (critical to the continuation of life) –Decomposers –Autotrophic bacteria

Miscellaneous Topics (2)  Symbiosis –Ecological relationship between organisms of different species that are in direct contact. –Mutualism  Both organisms benefit –Commensalism  One organism benefits while neither helping or hurting the other –Parasitism  The parasite benefits at the expense of the host

Miscellaneous Topics (3)  Disease –Opportunistic pathogens –Koch’s postulates  Find the same pathogen in each diseased individual  Isolate pathogen from a diseased subject and grow it in pure culture  Use the cultured pathogen to induce the disease in experimental animal  Re-isolate the same pathogen in the diseased experimental animals –Toxins  Exotoxins  Endotoxins

Haemophilus influenzae on nasal mucosa Haemophilus influenzae on nasal mucosa

Lyme disease, a bacterial disease transmitted by ticks

Use in Research and Technology  Model system for studying metabolism and molecular biology. (Escherichia coli is the best understood of all organisms)  Food industry uses bacteria to convert milk to yogurt and cheeses (video: Tasty Bacteria) (video: Tasty Bacteria) (video: Tasty Bacteria)  DNA technology  Bioremediation  Antibiotics (video: Antibiotics) (video: Antibiotics) (video: Antibiotics)  Etc etc etc

Putting prokaryotes to work in sewage treatment facilities Putting prokaryotes to work in sewage treatment facilities

Bioremediation for an oil spill Pseudomonads are used to decomposed petroleum products and a variety of synthetic compounds such as pesticides