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Bacteria
General Characteristics
Single-celled; no nucleus or complex organelles
Earliest known life forms
Smallest and simplest living organisms
Size 20 - 200 microns in diameter and 50 – 1,000 microns long
Few hundred genes
Bacterial Structure
All bacteria have an outer cell wall made out of glycoproteins or lipoprotein
Some bacteria have a sticky envelope around the cell wall called a capsule or slime
layer
Very simple internal organization
Cytoplasm with very few organelles
Nucleoid region (loosely coiled DNA)
Classification
Bacteria are placed into two major kingdoms:
Kingdom Archaebacteria - oldest bacteria, found in harsh environments
Kingdom Eubacteria -True bacteria, the largest group.
Grouped according to their shape and arrangement:
Coccus (i) = Spherical shaped cells
single cocci
diplococci (pairs)
Streptococci (chains)
Staphylococci (clusters)
Bacillus (i) = Rod shaped cells
single bacilli
Diplobacilli
Streptobacilli
Spirillium = spiral shaped
Bacteria can also be grouped according to their living arrangements
Saprophytes - live on dead things (decomposers)
Symbiotes - Two organisms living and depending on each other
Parasitic
Commensulistic
Mutualistic
Bacteria Prefer:
Warmth; 25-37 °C
Dark
Moisture
Food
Movement
Many forms have flagella for movement
Some bacteria have pili, which allow them to attach to other things
Feeding and digestion
Autotrophic
Photosynthetic (e.g. cyanobacteria or blue-green algae)
Chemosynthetic (e.g. methanogens or halophiles)
Heterotrophic
Extracellular digestion
Secret enzymes
Digest their food
They absorb the food back into their cells by diffusion
Circulation, Excretion and Respiration
By diffusion
Obligate aerobes
Must have oxygen to live
e.g. Mycobacterium tuberculosis
Obligate anaerobes
Can not live in the presence of oxygen
e.g. Clostridium botulinum
Facultative anaerobes
Can grow with or without O2 but do better without O2 e.g. Escherichia coli
Reproduction
Asexual
Binary fission - splitting into two equal cells
Sexual reproduction
Conjugation-exchange of plasmids
plasmids are independent circular pieces of DNA in bacteria.
after plasmid is exchanged one bacterium usually dies.
Harmful Effects of Bacteria
Pathogenic (cause diseases)
By directly damaging cells as they digest cells for food.
Or by indirectly damaging cells by releasing toxins which damage hosts.
They also trigger body's immune response, i.e. fever or inflammation.
Examples: botulism, tuberculosis, gonorrhea, typhoid fever, bubonic plague, diphtheria,
cholera, tetanus etc.
Other problems caused by bacteria
Food spoilage (many species)
Food poisoning Salmonella sp.
Disorders like boils, pimples, pneumonia, and some forms of arthritis.
Treatment of bacterial diseases
Antibiotics are usually made from fungi or other bacteria. why?
Examples: Penicillin, Streptomycin, tetracycline, and sulfa drugs.
Problems with Antibiotics
Antibiotic resistance.
Kills off good bacteria as well as bad.
Inhibits body's natural immunity.
Pasteurization and sterilization (UV & alcohol) help prevent the spread of disease.
Beneficial effects of bacteria
Decomposition of organic material
Nitrogen fixation in some plants (legumes)
Used to make antibiotics
Food production: e.g. Yogurt, Cottage cheese, Blue cheese,Vinegar
Used as a tool in genetic engineering
Tanning leather
Curing tobacco
Bioleaching-extracting minerals from ore deposits