Prokaryotes

Archaebacteria and Eubacteria

Characteristics of Bacteria

• Single-celled

• Prokaryotes– Nucleus and organelles not surrounded by

membranes

• DNA of bacteria made of a single chromosome

• Asexual reproduction (binary fission)

Structure of Bacteria

• 1-10 µm• 1 mm =1000 µm

Bacteria Shape

• Coccus: spherical cell– Monococci – separate– Diplococci – pairs– Streptococci – linear chains– Staphlococci – grape-like clusters

• Bacillus: rod shaped– Diplobacilli – pairs– Streptobacilli – linear chains

• Spirillum: spiral shaped– Exist only as single cells

Gram Stain

• Bacteria can be classified by their reaction to a dye called gram stain

• Cells that retain the stain appear purple (gram positive)

• Cells that don’t retain the stain appear light pink (gram negative)

Reproduction

• Binary fission: two offspring cells that are completely identical

• Extremely fast division (divide every 15-20 mins) eg. E. coli can produce 10 – 100 million bacteria in 12 hours

• Rapid division increased chances of mutation – an evolutionary gift.

Conjugation

• Under poor conditions, bacteria may resort to a form of sexual reproduction called conjugation

• The bacteria receiving the genetic information has a new genetic make-up which might possess a gene combination that is better suited to the changing environment.

• Eg. antibiotics

Pathogenic Bacteria

• Bacteria that cause infectious disease.• Vast majority of bacteria are harmless or beneficial.• One of the bacterial diseases with highest disease

burden is tuberculosis, caused by the bacterium Mycobacterium tuberculosis, which kills about 2 million people a year.

• Pathogenic bacteria contribute to other globally important diseases, such as pneumonia and food born illnesses, which can be caused by bacteria such as Shigella, Campylobacter and Salmonella.

• Pathogenic bacteria also cause infections such as tetanus, typhoid fever, diphtheria, syphilis and leprosy.

• Immune cells munch on E. coli bacteria