Chapter 24: Kingdom Monera (bacteria)
Bacteria have prokaryotic cells, usually 1 - 5 micrometers wide. Many species are mutualistic eg bacteria in gut of herbivores.
Bacteria are classified by : a) shape of cells Fig 24-8
- round : coccus eg Streptococcus mutans (causes tooth decay)
- rod shape : bacillus eg Bacillus thuringiensis ( Bt is used as an insecticide on crops).
Escherichia coli ( E. coli, a common bacteria in the intestines )
- spiral : spirillum eg Treponema pallidum (causes syphilis).
Images
b) Gram stain Fig 24-10
You stain the bacteria first with violet dye, then a red dye.
Bacteria with peptidoglycan on the outside of the cell wall stain violet or purple ( Gram positive ) eg Streptococcus.
Remember: Purple, Positive, Peptidoglycan.
Bacteria with cell membrane on the outside stain red ( Gram negative ) eg Escherichia
Many antibiotics such as Penicillin prevent bacteria from producing peptidoglycan. Antibiotics are often given to farm animals, which increases the risk of antibiotic resistant bacteria infecting humans. Animals
Types of bacteria
1) Archaebacteria - ancient, fossils 3.5 billion years old.
- usually obligate anaerobes (cannot survive in the air)
- have no peptidoglycan and no flagella.
- are divided into three main groups :
a) Methanogens - produce methane gas
- found in swamps, sewage treatment plants; they are
decomposers
- eg Methanosarcina.
b) Halophiles - live in very salty water; autotrophs
- grow best at 35 - 50 oC. Fig 24-17
- eg Halobacterium
c) Thermophiles - live in hot springs.
- grow best at 70 - 100 oC
- eg Pyrococcus and Thermus (used in Polymerase Chain Reaction)
2) Eubacteria - more modern, have peptidoglycan.
- they often form resistant endospores. Fig 24-15. May have flagella for movement.
There are many groups (Table 24-2), including :
- Cyanobacteria
( blue/green algae ); autotrophs (photosynthetic) - eg Anabaena.
- Enteric bacteria
- in the digestive system - Escherichia.
- Nitrogen fixing bacteria
- in soil and legumes. They convert nitrogen gas in the air to ammonia or nitrate, which can be used by plants.
- Rhizobium.
Commercial uses: Bacteria are used in bioremediation - removing toxic chemicals from soils. Other bacteria are used in manufacturing chemicals such as citric acid, human proteins (insulin, growth hormone), anti-cancer drugs, and also in biotechnology to produce genetically modified (GM) crops.
Energy use and Organic molecules
Chemoheterotrophs : take in organic molecules and use them for energy
- eg bacteria, fungi, animals
Chemoautotrophs : take in carbon dioxide and make organic molecules using energy from inorganic compounds
- eg bacteria
Photoautotrophs : take in carbon dioxide, and use light for energy
- eg green plants, bacteria
Photoheterotrophs : take in organic molecules, and use light for energy
- eg bacteria
Reproduction in bacteria
1) Binary fission - one cell splits in two ( asexual ).
Movie.
2) Conjugation - sex pili are used to transfer genes from one bacteria to another. Fig 24-14.
3) Transduction - viruses accidentally move genetic material from one bacteria to another. Fig 24-13.
Last edited January, 2011 by David Byres, dbyres@fscj.edu