Bacteria and Archaea

Life is divided into three domains. The Domains Bacteria and Archaea contain prokaryotic organisms (no nucleus). Domain Eukarya contains all eukarkyotic (have nucleus). Domain Archaea is more closely related to Eukarya than is Bacteria.

Three Domain System of Classification

The Archaea First prokaryotes that were classified as Archaea were known as “extremophiles” and live in extreme environments. Extreme halophiles live in high salt concentrations. Extreme thermophiles live in very hot conditions. Methanogens use carbon dioxide to oxidize H2 and produce methane as a waste product.

Structural and Functional adaptations of prokaryotes Most common shape of prokaryotes are spheres (cocci), rods (bacilli), and spriral shaped (spirilla).

Prokaryotes are about 1-5 micrometers – about 1/10 size of a typical eukaryotic cell. Prokaryotes have no true nucleus or internal compartments. DNA is concentrated in a region called the nucleoid and has little associated protein. Prokaryotes have small genomes.

Plasmids are small, circular, independent pieces of DNA. Plasmids can transfer genes for antibiotic resistance.

Prokaryotes reproduce through an asexual process can binary fission.

Bacteria can be divided into two large groups based on the structure of their cell wall. The cell wall of prokaryotes contains peptidoglycans. The cell wall type can be differentiated by a stain called the “Gram Stain” Gram positive bacteria have simpler cell walls with more peptidoglycan. Gram negative cells have walls that have less peptidoglycan and are structurally more complex.

Gram Stain

Pilli are appendages that allow bacteria to adhere to each other or to surrounding surfaces. Flagella are whiplike appendages used for motility.

Rapid reproduction, mutation, and genetic recombination produce genetic diversity in prokaryotes Major source of variation is mutation. Three mechanisms by which bacteria can transfer genetic information between each other are: Transformation Conjugation Transduction

Transformation Prokaryote takes up DNA from its environment.

Conjugation is the direct transfer of genes from one prokaryote to another

Transduction is the transfer of genes from viruses to prokaryotes. Virus infects cell Degrades host DNA Some new virus particles take up host DNA instead of viral DNA Virus with host DNA infects new bacterial cell and transfers DNA to new host.

Nutritional adaptations of prokaryotes Photoautotrophs – photosynthetic, use sunlight to convert CO2 into organic compounds. Chemoautotrophs use CO2 as source of carbon, but get energy from oxidizing inorganic substances.

Photoheterotrophs – use light to make ATP, but must obtain their carbon from an outside source already fixed in organic compounds. Chemoheterotrophs get both carbon and energy from organic compounds.

Metabolic adaptations of prokaryotes Obligate aerobes – cannot grow without oxygen, require it for cellular respiration. Obligate anaerobes – are poisoned by oxygen, use anaerobic respiration Facultative anaerobes – use oxygen if available, but fermentation if not.

Prokaryotes play crucial roles in the biosphere. Nitrogen Fixation – Some prokaryotes can use atmospheric nitrogen as a direct source of nitrogen. Decomposers Many participate in symbiotic relationships.

Some bacteria are pathogenic (disease causing) Produce toxins that cause tissue damage Examples: Streptococcus pyogenes – strep throat Vibrio cholera – cholera Mycobacterium tuberculosis – TB Bacillus anthracis - anthrax

Antibiotics Antibiotics are chemicals that kill prokaryotes They are not effective against viruses. Many bacterial plasmids contain resistance genes to antibiotics. Antibiotic resistance spreads rapidly through a bacterial population and is becoming a serious health risk.

Usefulness of Prokaryotes Bioremediation – removing pollutants from soil, air, or water Includes: sewage treatment cleaning up oil spills precipitating radioactive materials

Bioremediation

Usefulness of Prokaryotes continued Symbionts in gut, manufacture vitamins and digest foods. Gene cloning and producing transgenic organisms Production of cheese and yogurt