Bacteria

KINGDOMS ARCHAEBACTERIA & EUBACTERIA

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Bacterial Evolution & Classification 

• Most numerous organisms on earth
• Earliest life forms (fossils date 2.5 billion years old)
• Microscopic prokaryotes (no nucleus nor membrane-bound organelles)
• Contain ribosomes
• Infoldings of the cell membrane carry on photosynthesis & respiration
• Surrounded by protective cell wall containing peptidoglycan (protein-carbohydrate)
• Many are surrounded by a sticky, protective coating of sugars called the capsule or glycocalyx (can attach to other bacteria or host)
• Have only one circular chromosome
• Have small rings of DNA called plasmids
• May have short, hairlike projections called pili on cell wall to attach to host or another bacteria when transferring genetic material
• Most are unicellular

• Found in most habitats
• Most bacteria grow best at a pH of 6.5 to 7.0
• Main decomposers of dead organisms so recycle nutrients
• Some bacteria breakdown chemical & oil spills
• Some cause disease 
• Move by flagella, gliding over slime they secrete ( e.g. Myxobacteria)
• Some can form protective endospores around the DNA when conditions become unfavorable; may stay inactive several years & then re-activate when conditions favorable
• Classified by their structure, motility (ability to move), molecular composition, & reaction to stains (Gram stain)
• Grouped into 2 kingdoms — Eubacteria (true bacteria) & Archaebacteria (ancient bacteria)
• Once grouped together in the kingdom Monera

Kingdom Archaebacteria

•   Found in harsh environments (undersea volcanic vents, acidic hot springs, salty water)
• Cell walls without peptidoglycan
• Subdivided into 3 groups based on their habitat — methanogens, thermoacidophiles, & extreme halophiles

Methanogens

• Live in anaerobic environments (no oxygen)
• Obtain energy by changing H2 and CO2 gas into methane gas
• Found in swamps, marshes, sewage treatment plants, digestive tracts of animals
• Break down cellulose for herbivores (cows)
• Produce marsh gas or intestinal gas (methane)
  

Extreme Halophiles

•   Live in very salty water
•   Found in the Dead Sea, Great Salt Lake, etc.
• Use salt to help generate ATP (energy)
  

Thermoacidophiles (Thermophiles)

• Live in extremely hot  (1100C) and acidic (pH 2) water
• Found in hot springs in Yellowstone National Park, in volcanic vents on land, & in cracks on the ocean floor that leak scalding acidic water
  

Kingdom Eubacteria (true bacteria)

• Most bacteria in this kingdom
• Come in 3 basic shapes — cocci (spheres), bacilli (rod shaped), spirilla (corkscrew shape)

• Bacteria can occur in pairs ( diplo– bacilli or cocci)
•   Bacteria occurring in chains are called strepto- bacilli or cocci
• Bacteria in grapelike clusters are called staphylococci
• Most are heterotrophic (can’t make their own food)
• Can be aerobic (require oxygen) or anaerobic (don’t need oxygen)
• Subdivided into 4 phyla — Cyanobacteria (blue-green bacteria), Spirochetes, Gram-positive, & Proteobacteria
• Can be identified by Gram staining (gram positive or gram negative)  

Gram Staining

• Developed in 1884 by Danish microbiologist, Hans Gram
•   Bacteria are stained purple with Crystal Violet & iodine; rinsed with alcohol to decolorize; then restained with Safranin (red dye)
  

• Bacterial cell walls either stain purple or reddish-pink

Gram-positive bacteria (Gram +)

• Thick layer of peptidoglycan (protein-sugar) complex in cell walls & single layer of lipids
• Stain purple

• Lactobacilli are used to make yogurt, buttermilk ….
• Actinomycetes make antibiotics like tetracycline & streptomycin
• Disease-causing gram + bacteria produce poisons called toxins
• Clostridium causes tetanus or lockjaw
• Streptococcus cause infections such as “strep” throat

• Staphylococci cause “staph” infections

• Also cause toxic shock, bacterial pneumonia, botulism (food poisoning), & scarlet fever
• Can be treated with penicillin (antibiotics) & sulfa drugs

Gram-negative bacteria (Gram -)

• Cell walls have a thin layer of peptidoglycan & an extra layer of lipids on the outside
• Stain pink or reddish 

• Lipid layer prevents the purple stain & antibiotics from entering (antibiotic resistant)
• Some are photosynthetic but make sulfur, not oxygen
• Rhizobacteria grow in root nodules of legumes (soybeans, peanuts…) & fix nitrogen form the air for plants
• Rickettsiae are parasitic bacteria carried by ticks that cause Rocky Mountain spotted fever
• Spirochetes can cause syphilis & Lyme disease

Phylum Cyanobacteria

• Gram negative
•   Carry on photosynthesis & make oxygen
• Called blue-green bacteria
• Contain pigments called phycocyanin (red & blue) & chlorophyll a (green)
•    May be red, yellow, green, brown, black, or blue-green
• Some grow in chains (e.g. Oscillatoria)  & have specialized cells called heterocysts that fix nitrogen

OSCILLATORIA

•  First bacteria to re-enter devastated areas
• Anabaena that live on nitrates & phosphates in water can overpopulate & cause “population blooms” or eutrophication
•   After eutrophication, the cyanobacteria die, decompose, & use up all the oxygen for fish

Phylum Spirochetes

•   Gram positive
• Have flagella at each end so move in a corkscrew motion
•   Some are aerobic (require oxygen); others are anaerobic
• May be free-living, parasitic, or live symbiotically with another organism  

Phylum Gram Positive bacteria

• Most are Gram +, but some are Gram –
• Lactobacilli grow in milk & make lactic acid (forms yogurt, cottage cheese, buttermilk) & also found on teeth & cause tooth decay
• Actinomycetes grow in the soil & make antibiotics
• Gram + members are found in the oral & intestinal cavities & slow the growth of disease-causing bacteria

Phylum Proteobacteria

• Largest & most diverse bacterial group
• Subdivided into Enteric bacteria, Chemoautotrophic bacteria, & Nitrogen-fixing bacteria  

Enteric bacteria

• Gram negative heterotrophs
• Can live in aerobic & anaerobic environments
• Includes E. coli that lives in the intestinal tract making vitamin K & helping break down food
• Salmonella causes food poisoning

Chemoautotrophs

• Gram negative bacteria that obtain energy from minerals  
• Iron-oxidizing bacteria found in freshwater ponds use iron salts for energy

Nitrogen-Fixing bacteria

• Rhizobium are Gram negative & live in legume root nodules

• 80% of atmosphere is N2, but plants can’t use nitrogen gas
• Nitrogen-fixing bacteria change N2 into usable ammonia (NH3)
• Important part of the Earth’s nitrogen cycle

Methods of Nutrition

•  Saprobes feed on dead organic matter
•  Parasites feed on a host cell
•  Photoautotrophs use sunlight for energy, but get carbon from organic compounds (not CO2) to make their own food  
• Chemoautotrophs obtain food by oxidizing inorganic substances like sulfur, instead of using sunlight

Methods of Respiration

•   Obligate aerobic bacteria can’t live without oxygen; (tuberculosis bacteria)
•  Obligate anaerobes die if oxygen is present; (tetanus bacteria that causes lockjaw)
• Facultative anaerobes do not need oxygen, but don’t die if oxygen is present; (E. coli)
• Anaerobes carry on fermentation, while aerobes carry on cellular respiration 

Bacterial Reproduction & Genetic Recombination

• Most bacteria reproduce asexually by binary fission (chromosome replicates & then the cell divides)  
•   Bacteria replicate (double in number) every 20 minutes under ideal conditions  
• Bacteria contain much less DNA than eukaryotes
• Bacterial plasmids are used in genetic engineering to carry new genes into other organisms  
• Bacteria recombine genetic material in 3 ways — transformation, conjugation, & transduction

Conjugation

• Sexual reproductive method
• Two bacteria form a conjugation bridge or tube between them

•   Pili hold the bacteria together
•   DNA is transferred from one bacteria to the other       

Transformation

• Bacteria pick up pieces of DNA from other dead bacterial cells
• New bacterium is genetically different from original

Transduction

• A bacteriophages (virus) carries a piece of DNA from one bacteria to another

• Human insulin is produced in the lab by this method

Pathogenic bacteria

•   Known as germs or pathogens
• Cause disease
• Can produce poisonous toxins
• Endotoxins are made of lipids & carbohydrates by Gram – bacteria & released after the bacteria die (cause high fever, circulatory vessel damage…)
• E. coli  produce endotoxins
• Exotoxins are made of protein by Gram + bacteria 
• Clostridium tetani produce exotoxins
• Antibiotics interfere with cellular functions (Penicillin interferes with synthesis of the cell wall; tetracycline interferes with protein synthesis)
• Some antibiotics are made by bacteria or fungi
• Broad-spectrum antibiotics affect a wide variety of organisms
• Bacteria can mutate and become antibiotic resistant (often results from overuse of antibiotics)